Language reference

This documentation describes the PC-BASIC language, which aims to faithfully emulate GW-BASIC 3.23, IBM Advanced BASIC, IBM Cartridge BASIC and Tandy 1000 GW-BASIC.

Differences with the original languages do arise, and where this is the case they are documented.

Please note that Microsoft's official documentation for the original languages is rather hit-and-miss; it leaves several features undocumented and incorrectly describes others. To avoid making the same errors, the present documentation was written from scratch with reference to the actual behaviour. The errors in this document are therefore all my own. Please contact me if you encounter them.

Metasyntax

In descriptions of BASIC syntax, the following conventions apply. Exact rendering of the markup may vary depending on the means used to display this documentation.

bold
Type exactly as shown.
italic
Replace with appropriate metavariable.
[a]
Entities within square brackets are optional.
{ a | b }
Disjunct alternatives of which one must be chosen.
[ a | b ]
Optional disjunct alternatives.
a ...
Preceding entity can be repeated.


Definitions

A program line consists of a line number followed by a compound statement. Program lines are terminated by a CR or or by the end of the file (optionally through an EOF character). Anything on a program line after a NUL character is ignored.

A line number is a whole number in the range [0—65535]. Note that the line numbers 65530—65535 cannot be entered from the console or a text program file, but can be part of a tokenised program file.

A compound statement consists of statements separated by colons: statement [: statement] ...

An expression takes one of the following forms: unary_operator {literal | variable | array_element | function} expression binary_operator expression (expression) whose elements are described the sections Literals, Variables, Operators and Functions.

An array element takes the form array {[|(} numeric_expression [, numeric_expression ] ... {)|]}


Literals

String literals

String literals are of the following form: "[characters]{NUL|CR|EOF|"} where characters is a string of characters. Any character from the current code page can be used, with the following exceptions, all of which terminate the string literal (aside from other effects they may have):

Strings are also legally terminated by the end of the file in the absence of an EOF character.

Apart from these, string literals should not contain any of the characters in the ASCII range &h0D&h1F, which lead to unpredictable results. There is no escaping mechanism. To include one of the above characters in a string, use string concatenation and the CHR$ function.

Numeric literals

Numeric literals have one of the following forms: [+|-] [0|1|2|3|4|5|6|7|8|9]... [.][0|1|2|3|4|5|6|7|8|9]... [{E|e|D|d}[+|-][0|1|2|3|4|5|6|7|8|9]...] |#|!|%] &{H|h}[0|1|2|3|4|5|6|7|8|9|A|B|C|D|E|F|a|b|c|d|e|f]... &[O|o] [0|1|2|3|4|5|6|7]...

Hexadecimal literals must not contain spaces, but decimal and octal literals may. The o character in octal literals is optional: they can be specified equally as &o777 or &777.

Hexadecimal and octal literals denote integers and do not include a sign. They must range between [&h0&hFFFF], of which the range [&h8000&hFFFF] is interpreted as a two's complement negative integer; for example, &hFFFF = -1. Signs can appear left of the & but these form an expression and are not part of the literal itself.

Floating-point literals must be specified in decimal notation. The decimal separator is the point. A base-10 exponent may be specified after E in single-precision floats, or after D in double-precision floats. Trailing % is ignored and does not indicate an integer literal. Trailing ! or # mark the literal as single- or double-precision, respectively.

Examples of valid numeric literals are -1 42 42! 42# 1.3523523 .235435 -.3 3. . .e .D 1.1e+7 1.1d+7 1e2 1e-2 &7 &hffff &O20 &h & 65537% 1.1%

Note that expressions such as &o-77 are legal; these are however not negative octals but rather the expression &o (empty octal; zero) less 77 (decimal 77).


Variables

Variable names must start with a letter; all characters of the variable name (except the sigil) must be letters A—Z, figures 0—9, or a dot . Only the first 40 characters in the name are significant. A variable name must not be identical to a reserved word or a reserved word plus sigil. Therefore, for example, you cannot name a variable TO! but you can name it AS!. Variable names may contain any reserved word. Variable names may also start with a reserved word, with the exception of USR and FN. Thus, FNORD% and USRNME$ are not legal variable names while FRECKLE% and LUSR$ are.

For each name, four different variables may exist corresponding to the four types. That is, you can have A$, A%, A! and A# as different variables. Which one of those is also known as A depends on the settings in DEFINT/DEFDBL/DEFSNG/DEFSTR. By default, A equals the single-precision A!.

Furthermore, the arrays A$(), A%(), A!(), A#() are separate from the scalar variables of the same name.

Types and sigils

PC-BASIC recognises four variable types, distinguished by their sigil or type character, the last character of the variable's full name:

sigil type size range precision
$ string 3 bytes plus allocated string space 0—255 characters
% integer 2 bytes -32768—32767 exact
! single-precision float 4 bytes ±2.938726·10-39—±1.701412·1038 ~6 significant figures
# double-precision float 8 bytes ±2.938735877055719·10-39—±1.701411834604692·1038 ~16 significant figures

Note that double-precision floats can hold more decimals than single-precision floats, but not larger or smaller numbers.

While all integers are signed, some statements will interpret negative integers as their two's complement.

Arrays

Arrays are indexed with round or square brackets; even mixing brackets is allowed. The following are all legal array elements: A[0], A(0), A(0], A[0). Multidimensional arrays are specified by separating the indices with commas: A(0, 0), A[0, 0, 0], etc.

By default, arrays are indexed from 0. This can be changed to 1 using OPTION BASE 1.

Arrays can be allocated by specifying the largest allowed index using DIM. If all indices of the array are 10 or less, they need not be explicitly allocated. The first access of the array (read or write) will automatically allocate it with a maximum index of 10 and the same number of indices as in the first access. To re-allocate an array, the old array must first be deleted with CLEAR or ERASE.

Multi-dimensional arrays are stored in column-major order, such that A%(2,0) immediately follows A%(1,0).

Conversions

PC-BASIC will implicitly convert between the three numerical data types. When a value of one type is assigned to a variable, array element or parameter of another type, it is converted according to the following rules:


Operators

Order of precedence

The order of precedence of operators is as follows, from tightly bound (high precedence) to loosely bound (low precedence):

  1. ^
    • *
    • /
    • \
    • MOD
      • +
      • - (unary and binary)
      • =
      • <>
      • ><
      • <
      • >
      • <=
      • =<
      • >=
      • =>
    • NOT (unary)
    • AND
    • OR
    • XOR
    • EQV
    • IMP

Expressions within parentheses () are evaluated first. All binary operators are left-associative: operators of equal precedence are evaluated left to right.

Examples
Errors

Mathematical operators

Mathematical operators operate on numeric expressions only. Note however that + can take the role of the string concatenation operator if both operands are strings.

Code Operation Result
x ^ y Exponentiation x raised to the power of y
x * y Multiplication Product of x and y
x / y Division Quotient of x and y
x \ y Truncated division Integer quotient of x and y
x MOD y Modulo Integer remainder of x by y (with the sign of x)
x + y Addition Sum of x and y
x - y Subtraction Difference of x and y
+ y Unary Plus Value of y
- y Negation Negative value of y
Notes
Errors

Relational operators

Relational operators can operate on numeric as well as string operands; however, if one operand is string and the other numeric, Type mismatch is raised.

Relational operators return either 0 (for false) or -1 for true.

Code Operation Result
= Equal True if a equals b, false otherwise.
<> >< Not equal False if a equals b, true otherwise.
< Less than True if a is less than b, false otherwise.
> Greater than True if a is greater than b, false otherwise.
<= =< Less than or equal False if a is greater than b, true otherwise.
>= => Greater than or equal False if a is less than b, true otherwise.

When operating on numeric operands, both operands are compared as floating-point numbers according to the usual ordering of numbers. The equals operator tests for equality to within machine precision for the highest-precision of the two operator types.

When comparing strings, the ordering is as follows.

Bitwise operators

PC-BASIC has no Boolean type and does not implement Boolean operators. It does, however, implement bitwise operators.

Bitwise operators operate on numeric expressions only. Floating-point operands are rounded to integers before being used.

Code Operation Result
NOT y Complement -y-1
x AND y Bitwise conjunction The bitwise AND of x and y
x OR y Bitwise disjunction The bitwise OR of x and y
x XOR y Bitwise exclusive or The bitwise XOR of x and y
x EQV y Bitwise equivalence NOT(x XOR y)
x IMP y Bitwise implication NOT(x) OR y

These operators can be used as Boolean operators only if -1 is used to represent true while 0 represents false. Note that PC-BASIC represents negative integers using the two's complement, so NOT 0 = -1. The Boolean interpretation of bitwise operators is given in the table below.

Code Operation Result
NOT y Logical negation True if y is false and vice versa
x AND y Conjunction Only true if both x and y are true
x OR y Disjunction Only false if both x and y are false
x XOR y Exclusive or True if the truth values of x and y differ
x EQV y Equivalence True if the truth values of x and y are the same
x IMP y Implication True if x is false or y is true

Be aware that when used on integers other than 0 and -1, bitwise operators can not be interpreted as Boolean operators. For example, 2 AND 1 returns 0.

Errors

String operators

The string concatenation operator is +. It has a binary as well as a unary form. The unary minus may also be used on strings, but has no effect.

Code Operation Result
x + y Concatenation The string formed by x followed by y
+ y Unary Plus Value of y
- y Unary Minus Value of y
Errors

Functions

Functions can only be used as part of an expression within a statement; they may take input values between parentheses and produce a return value. For example, in PRINT ABS(-1) the ABS function is used in an expression within a PRINT statement; in Y = SQR(X) + 2 the SQR function is used in an expression within a LET statement.

Some reference works also use terms such as system variable for functions that do not take an input, presumably since in the GW-BASIC syntax such functions have no parentheses, in contrast to the languages in the C family (and indeed some modern BASICs). However, this is simply the GW-BASIC syntax for functions without inputs. For example, one can do DEF FNA=1: PRINT FNA in which no parentheses are allowed.

ABS

y = ABS(x)

Returns the absolute value of x if x is a number and the value of x if x is a string.

Parameters
  • x is an expression.

ASC

val = ASC(char)

Returns the code point (ASCII value) for the first character of char.

Parameters
  • char is an expression with a string value.
Errors
  • char has a numeric value: Type mismatch.
  • char equals "": Illegal function call.

ATN

y = ATN(x)

Returns the inverse tangent of x.

Parameters
  • x is a numeric expression that gives the angle in radians.
Notes
  • Unless PC-BASIC is run with the double option, this function returns a single-precision value.
  • ATN(x) differs in the least significant digit from GW-BASIC.
Errors
  • x has a string value: Type mismatch.

CDBL

y = CDBL(x)

Converts the numeric expression x to a double-precision value.

Errors
  • x has a string value: Type mismatch.

CHR$

char = CHR$(x)

Returns the character with code point x.

Parameters
  • x is a numeric expression in the range [0—255].
Errors
  • x has a string value: Type mismatch.
  • x is not in [-32768—32767]: Overflow.
  • x is not in [0—255]: Illegal function call.

CINT

y = CINT(x)

Converts the numeric expression x to a signed integer. Halves are rounded away from zero, so that e.g. CINT(2.5) = 3 and CINT(-2.5) = -3.

Errors
  • x has a string value: Type mismatch.
  • x is not in [-32768—32767]: Overflow.

COS

cosine = COS(angle)

Returns the cosine of angle. Unless PC-BASIC is run with the double option, this function returns a single-precision value.

Parameters
  • angle is a numeric expression that gives the angle in radians.
Notes
  • The return value usually differs from the value returned by GW-BASIC in the least significant figure.
Errors
  • angle has a string value: Type mismatch.

CSNG

y = CSNG(x)

Converts the numeric expression x to a single-precision value by Gaussian rounding.

Errors
  • x has a string value: Type mismatch.

CSRLIN

y = CSRLIN

Returns the screen row of the cursor on the active page. The return value is in the range [1—25].

Notes
  • This function takes no arguments.

CVI

y = CVI(s)

Converts a two-byte string to a signed integer.

Parameters
  • s is a string expression that represents an integer using little-endian two's complement encoding. Only the first two bytes are used.
Errors
  • s has a numeric value: Type mismatch.

CVS

y = CVS(s)

Converts a four-byte string to a single-precision floating-point number.

Parameters
  • s is a string expression that represents a single-precision number in Microsoft Binary Format. Only the first four bytes are used.
Errors
  • s has a numeric value: Type mismatch.

CVD

y = CVD(s)

Converts an eight-byte string to a double-precision floating-point number.

Parameters
  • s is a string expression that represents a double-precision number in Microsoft Binary Format. Only the first eight bytes are used.
Errors
  • s has a numeric value: Type mismatch.

DATE$ (function)

s = DATE$

Returns the system date as a string in the format "mm-dd-yyyy".

Notes
  • This function takes no arguments.

ENVIRON$

value = ENVIRON[ ]$(x)

Returns an environment variable.

Parameters

x is an expression.

  • If x has a string value, returns the value for the environment variable x or the empty string if no variable with the name x is set in the environment table. The environment variable must be an ASCII string and will be converted to uppercase on case-sensitive systems.
  • If x has a numeric value, it must be in [1—255]. Returns the xth entry in the environment table.
Errors
  • x is the empty string: Illegal function call.
  • x contains non-ASCII characters: Illegal function call.
  • x is a number not in [-32768—32767]: Overflow.
  • x is a number not in [1—255]: Illegal function call.

EOF

is_at_end = EOF(file_num)

Returns -1 if file with number file_num has reached end-of-file; 0 otherwise. The file must be open in INPUT or RANDOM mode. EOF(0) returns 0.

Notes
  • If file_num is open to KYBD:, performs a blocking read and returns -1 if CTRL+Z is entered, 0 otherwise. The character entered is then echoed to the console.
Errors
  • file_num has a string value: Type mismatch.
  • file_num is a number not in [-32768—32767]: Overflow.
  • file_num is a number not in [0—255]: Illegal function call.
  • file_num is not 0 or the number of an open file: Bad file number.
  • The file with number file_num is in OUTPUT or APPEND mode: Bad file mode.

ERDEV

zero = ERDEV

Returns 0.

Notes
  • In GW-BASIC, returns the value of a device error.
  • This function is not implemented in PC-BASIC.
  • This function takes no arguments.

ERDEV$

empty = ERDEV[ ]$

Returns the empty string.

Notes
  • In GW-BASIC, returns the device name of a device error.
  • This function is not implemented in PC-BASIC.
  • This function takes no arguments.

ERL

error_line = ERL

Returns the line number where the last error was raised.

Notes
  • If the error was raised by a direct statement, returns 65535.
  • If no error has been raised, returns 0.
  • This function takes no arguments.

ERR

error_code = ERR

Returns the number of the last error.

Notes
  • If no error has been raised, returns 0.
  • If the last error was a Syntax error raised by a direct statement, returns 0.
  • This function takes no arguments.

EXP

y = EXP(x)

Returns the exponential of x, i.e. e to the power x.

Parameters
  • x is a number- valued expression.
Notes
  • Unless PC-BASIC is run with the double option, this function returns a single-precision value.
  • The return value sometimes differs in the least significant digit from GW-BASIC. For large values of x, the difference may be 3 digits.
Errors
  • x has a string value: Type mismatch.
  • x is larger than the natural logarithm of the maximum single-precision value: Overflow.

EXTERR

zero = EXTERR(x)

Returns 0.

Parameters
  • x is a numeric expression in [0—3].
Notes
  • In GW-BASIC, this function returns extended error information from MS-DOS.
  • This function is not implemented in PC-BASIC.
Errors
  • x has a string value: Type mismatch.
  • x is not in [-32768—32767]: Overflow.
  • x is not in [0—3]: Illegal function call.

FIX

whole = FIX(number)

Returns number truncated towards zero.

Parameters
  • number is a numeric expression.
Notes
  • FIX truncates towards zero: it removes the fractional part. By contrast, INT truncates towards negative infinity.
Errors
  • number is a string expression: Type mismatch.

FN

result = FN[ ]name [(arg_0 [, arg_1] ...)]

Evaluates the user-defined function previously defined with DEF FN name. Spaces between FN and name are optional.

Parameters
  • name is the name of a previously defined function.
  • arg_0, arg_1, ... are expressions, given as parameters to the function.
Errors
  • No function named name is defined: Undefined user function.
  • The number of parameters differs from the function definition: Syntax error.
  • The type of one or more parameters differs from the function definition: Type mismatch.
  • The return type is incompatible with the function name's sigil: Type mismatch.
  • The function being called is recursive or mutually recursive: Out of memory.

FRE

free_mem = FRE(x)

Returns the available BASIC memory.

Parameters

x is an expression.

  • If x has a numeric value, it is ignored.
  • If x has a string value, garbage collection is performed before returning available memory.

HEX$

hex_repr = HEX$(x)

Returns a string with the hexadecimal representation of x.

Parameters
  • x is a numeric expression in [-32768—65535]. Values for negative x are shown as two's-complement.
Errors
  • x is not in [-32768—65535]: Overflow.
  • x has a string value: Type mismatch.

INKEY$

key = INKEY$

Returns one key-press from the keyboard buffer. If the keyboard buffer is empty, returns the empty string. Otherwise, the return value is a one- or two- character string holding the e-ASCII code of the pressed key.

Notes
  • This function takes no arguments.
  • When a function key F1F10 is pressed, INKEY$ will return the letters of the associated macro — unless this macro has been set to empty with the KEY statement, in which case it returns the e-ASCII code for the function key.

INP

code = INP(port)

Returns the value of an emulated machine port.

Parameters

port is a numeric expression in [0—65535].

port Effect
&h60 Returns the keyboard scancode for the current key pressed or the last key released. The scancodes returned by INP(&h60) are those listed in the keyboard scancodes table. If a key is currently down, the return value is its scancode. If no key is down, the return value is the scancode of the last key released, incremented by 128.
&h201 Returns the value of the game port (joystick port). This value is constructed as follows:
Bit Meaning
0 joystick 2 x-axis
1 joystick 1 y-axis
2 joystick 1 x-axis
3 joystick 2 y-axis
4 joystick 2 button 1
5 joystick 1 button 2
6 joystick 1 button 1
7 joystick 2 button 2
The button bits are 0 when the button is fired, 1 otherwise. The axis values are normally 0 but are set to 1 by OUT &h201, x and then fall back to 0 after a delay. The longer the delay, the higher the axis value.
other values Returns zero.
Notes
  • Only a limited number of machine ports are emulated in PC-BASIC.
Errors
  • port is not in [-32768—65535]: Overflow.
  • port has a string value: Type mismatch.

INPUT$

chars = INPUT[ ]$ (num_chars [, [#] file_num])

Returns a string of num_chars characters from the keyboard or, if file_num is provided, from a text file.

Parameters
  • num_chars is a numeric expression in [1—255].
  • file_num is a numeric expression that returns the number of a text file opened in INPUT mode. The # is optional and has no effect.
Notes
  • This is a blocking read. It will wait for characters if there are none in the buffer.
  • All control characters except Ctrl+Break, Ctrl+Scroll Lock and Pause are passed to the string by INPUT$. Ctrl+Break and Ctrl+Scroll Lock break execution whereas Pause halts until another key is pressed (and not read).
  • When reading from the keyboard directly or through KYBD:, arrow keys, Del, Home, End, Pg Up, Pg Dn are passed as NUL characters. Function keys are ignored if they are event-trapped, otherwise function-key macro replacement is active as normal.
Errors
  • num_chars is not in [-32768—32767]: Overflow.
  • num_chars is not in [1—255]: Illegal function call.
  • file_num is not an open file: Bad file number.
  • file_num is less than zero: Illegal function call.
  • file_num is greater than 32767: Overflow.
  • file_num is not open for INPUT: Bad file mode.
  • num_chars or file_num are strings: Type mismatch.
  • file_num is open to a COM port and this is the first INPUT, LINE INPUT or INPUT$ call on that port since the buffer has filled up completely (i.e. LOF(file_num) has become zero): Communication buffer overflow.

INSTR

position = INSTR([start,] parent, child)

Returns the location of the first occurrence of the substring child in parent.

Parameters
  • parent and child are string expressions.
  • start is a numeric expression in [1—255], specifying the starting position from where to look; if not specified, the search starts at character 1.
Notes
  • If child is not a substring of parent occurring at or before start, INSTR returns 0.
Errors
  • start has a string value or parent or child have numeric values: Type mismatch.
  • start is not in [-32768—32767]: Overflow.
  • start is not in [1—255]: Illegal function call.

INT

whole = INT(number)

Returns number truncated towards negative infinity.

Parameters
  • number is an expression.
Notes
  • FIX truncates towards zero: it removes the fractional part. By contrast, INT truncates towards negative infinity.
  • If number is a string expression, INT returns its value unchanged.

IOCTL$

result = IOCTL[ ]$ ([#] file_num)

Raises Illegal function call.

Notes
  • In GW-BASIC, IOCTL$ reads the reply to IOCTL from a device.
  • This function is not implemented in PC-BASIC.
Errors
  • file_num has a string value: Type mismatch.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not an open file: Bad file number.
  • Otherwise: Illegal function call

LEFT$

child = LEFT$(parent, num_chars)

Returns the leftmost num_chars characters of parent.

Parameters
  • parent is a string expression.
  • num_chars is a numeric expression in [0—255].
Notes
  • If num_chars is zero or parent is empty, LEFT$ returns an empty string.
  • If num_chars is greater than the length of parent, returns parent.
Errors
  • parent has a numeric value or num_chars has a string value: Type mismatch.
  • num_chars is not in [-32768—32767]: Overflow.
  • num_chars is not in [0—255]: Illegal function call.

LEN

length = LEN(string)

Returns the number of characters in string.

Parameters
  • string is a string expression.
Errors
  • string has a number value: Type mismatch.

LOC

location = LOC(file_num)

Returns the current location in the file opened under number file_num.

  • If the file is opened for INPUT, OUTPUT or APPEND, LOC returns the number of 128-byte blocks read or written since opening the file.
  • If the file is opened for RANDOM, LOC returns the record number last read or written.
  • If the file is opened to a COM device, LOC returns the number of characters in the input buffer, with a maximum of 255.
  • If the file is opened to KYBD:, LOC returns 0.
Parameters
  • file_num is a numeric expression in the range [0—255].
Notes
  • file_num must not be preceded by a #.
  • In OUTPUT or APPEND mode, before any writes LOC returns 0. After the 128th character is written, LOC returns 1.
  • In INPUT mode, before any reads LOC returns 1. After the 129th character is read, LOC returns 2.
  • If text-encoding is set, characters may be encoded by sequences of more than one byte. LOC will return the number of bytes rather than the number of encoded characters.
Errors
  • file_num has a string value: Type mismatch.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not in [0—255]: Illegal function call.
  • file_num is not an open file: Bad file number.
  • file_num is open to a LPT device: Bad file mode.

LOF

length = LOF(file_num)

Returns the number of bytes in the file open under file_num.

Parameters
  • file_num is a numeric expression in the range [0—255].
Notes
  • If file_num is open to a COM: device, LOF returns the number of bytes free in the input buffer.
Errors
  • file_num has a string value: Type mismatch.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not in [0—255]: Illegal function call.
  • file_num is not an open file: Bad file number.
  • file_num is open to a LPT device: Bad file mode.
Notes
  • If text-encoding is set, characters may be encoded by sequences of more than one byte. LOF will return the number of bytes rather than the number of encoded characters.

LOG

y = LOG(x)

Returns the natural logarithm of x.

Parameters
  • x is a numeric expression greater than zero.
Notes
  • Unless PC-BASIC is run with the double option, this function returns a single-precision value.
  • LOG(x) can differ from GW-BASIC by 1 in the least significant digit.
Errors
  • x has a string value: Type mismatch.
  • x is zero or negative: Illegal function call.

LPOS

position = LPOS(printer_number)

Returns the column position for a printer.

Parameters
  • printer_number is a numeric expression in [0—3]. If it is 0 or 1, the position for LPT1: is returned. If it is 2, LPT2:; 3, LPT3:.
Notes
  • When entering direct mode, LPT1: (but not other printers) is flushed and its position is reset to 1.
Errors
  • printer_number has a string value: Type mismatch.
  • printer_number is not in [-32768—32767]: Overflow.
  • printer_number is not in [0—3]: Illegal function call.

MID$ (function)

substring = MID$(string, position [, length])

Returns a substring of string starting at position, counting from 1. The substring has length length if specified. If length is not specified, the substring extends to the end of the string.

Parameters
  • string is a string expression.
  • position is a numeric expression between 1 and the string length, inclusive.
  • length is a numeric expression in [0—255].
Errors
  • string has a number value or position or length have string values: Type mismatch.
  • position or length are not in [-32768—32767]: Overflow.
  • position is not in [1—255]: Illegal function call.
  • length is not in [0—255]: Illegal function call.

MKD$

bytes = MKD$(double)

Returns the internal 8-byte Microsoft Binary Format representation of a double- precision number.

Errors
  • double has a string value: Type mismatch.

MKI$

bytes = MKI$(int)

Returns the internal 2-byte little-endian representation of an integer.

Errors
  • int has a string value: Type mismatch.
  • int is not in [-32768—32767]: Overflow.

MKS$

bytes = MKS$(single)

Returns the internal 8-byte Microsoft Binary Format representation of a single- precision number.

Errors
  • single has a string value: Type mismatch.

OCT$

octal = OCT$(x)

Returns a string with the octal representation of x.

Parameters
  • x is a numeric expression in [-32768—65535]. Values for negative x are shown as two's-complement.
Errors
  • x has a string value: Type mismatch.
  • x is not in [-32768—65535]: Overflow.

PEEK

value = PEEK(address)

Returns the value of the memory at segment * 16 + address where segment is the current segment set with DEF SEG.

Parameters
  • address is a numeric expression in [-32768—65535]. Negative values are interpreted as their two's complement.
Notes
  • The memory is only partly emulated in PC-BASIC. See Memory model for supported addresses. Outside emulated areas, PEEK returns 0.
  • Values for particular memory address can be preset on the command line using the peek option. This can be used for compatibility with old programs. These values will override video or data segment values, if they are in those locations.
Errors
  • address has a string value: Type mismatch.
  • address is not in [-32768—65535]: Overflow.

PEN (function)

x = PEN(mode)

Reads the light pen. What this function returns depends on mode:

mode Return value
0 Boolean; whether the light pen has been down since last poll.
1 x coordinate of last pen down position
2 y coordinate of last pen down position
3 Boolean; whether the pen is currently down
4 x coordinate of current pen position
5 y coordinate of current pen position
6 character row coordinate of last pen down position
7 character column coordinate of last pen down position
8 character row coordinate of current pen position
9 character column coordinate of current pen position
Parameters
  • mode is a numeric expression in [0—9].
Notes
  • In PC-BASIC, for pen down read mouse button pressed. For pen position read mouse pointer position.
Errors
  • mode has a string value: Type mismatch.
  • mode is not in [-32768—32767]: Overflow.
  • mode is not in [0—9]: Illegal function call.

PLAY (function)

length = PLAY(voice)

Returns the number of notes in the background music queue. The return value is in [0—32].

Parameters
  • voice is a numeric expression in [0—255]. If syntax={pcjr|tandy}, indicates for which tone voice channel the number of notes is to be returned. If voice is not in [0—2], the queue for voice 0 is returned. For other choices of syntax, the voice value has no effect.
Notes
  • There are at most 32 notes in the music queue. However, unless the articulation is set to legato, there are short gaps between each note; these are counted as separate notes in the queue. Effectively, the queue length is thus 16 for the default and staccato articulations and 32 for legato.
Errors
  • voice has a string value: Type mismatch.
  • voice is not in [0—255]: Illegal function call.
  • voice is not in [-32768—32767]: Overflow.

PMAP

transformed_coord = PMAP(original_coord, fn)

Maps between viewport and logical (WINDOW) coordinates. If no VIEW has been set, the viewport coordinates are physical coordinates.

Depending on the value of fn, PMAP transforms from logical to viewport coordinates or vice versa:

fn Return value
0 return viewport x given logical x
1 return viewport y given logical y
2 return logical x given viewport x
3 return logical y given viewport y
Parameters
  • fn is a numeric expression in [0—3].
Notes
  • Initially, in text mode, PMAP returns 0.
  • In GW-BASIC, PMAP behaves anomalously on SCREEN changes, where it sometimes returns results as if the last WINDOW setting had persisted. This behaviour is not implemented in PC-BASIC.
Errors
  • Any of the parameters has a string value: Type mismatch.
  • A physical coordinate is not in [-32768—32767]: Overflow.
  • fn is not in [-32768—32767]: Overflow.
  • fn is not in [0—3]: Illegal function call.

POINT (current coordinate)

coord = POINT(fn)

Returns a currently active coordinate of the graphics screen. This is usually the last position at which a pixel has been plotted, the second corner given in a LINE command, or the centre of the viewport if nothing has been plotted. fn is a numeric expression in [0—3].

The coordinate returned depends on the value of fn:

fn Return value
0 viewport x
1 viewport y
2 logical x
3 logical y
Parameters
  • fn is a numeric expression in [0—3].
Notes
  • In text mode, returns the active coordinate of any previous graphics mode; if no graphics mode has been active, returns 0.
Errors
  • fn has a string value: Type mismatch.
  • fn is not in [-32768—32767]: Overflow.
  • fn is not in [0—3]: Illegal function call.

POINT (pixel attribute)

attrib = POINT(x, y)

Returns the attribute of the pixel at logical coordinate x,y.

Parameters
  • x, y are numeric expressions in [-32768—32767].
Notes
  • If x,y is outside the screen, returns -1.
Errors
  • Function is called in text mode: Illegal function call.
  • x or y has a string value: Type mismatch.
  • x or y or the physical coordinates they translate into are not in [-32768—32767]: Overflow.

POS

pos = POS(dummy)

Returns the current cursor column position, in the range [1—80].

Parameters
  • dummy is a valid expression of any type; its value has no effect.

RIGHT$

child = RIGHT$(parent, num_chars)

Returns the rightmost num_chars characters of parent. If num_chars is zero or parent is empty, RIGHT$ returns an empty string. If num_chars is greater than the length of parent, returns parent.

Parameters
  • parent is a string expression.
  • num_chars is a numeric expression in [0—255].
Errors
  • num_chars has a string value: Type mismatch.
  • num_chars is not in [-32768—32767]: Overflow.
  • num_chars is not in [0—255]: Illegal function call.

RND

random = RND[(x)]

Returns a pseudorandom number in the interval [0—1).

Parameters

x is a numeric expression.

  • If x is zero, RND repeats the last pseudo-random number.
  • If x is greater than zero, a new pseudorandom number is returned.
  • If x is negative, x is converted to a single-precision floating-point value and the random number seed is set to the absolute value of its mantissa. The function then generates a new pseudorandom numer with this seed. Since the only the mantissa of x is used, any two values whose ratio is a power of 2 will produce the same seed. Note that this procedure for generating a new seed differs from that used by RANDOMIZE.
Notes
  • PC-BASIC's RND function generates pseudo-random numbers through a linear congruential generator with modulo 224, multiplier 214013 and increment 2531011. This exactly reproduces the random numbers of GW-BASIC's RND.
  • It should be noted, however, that this is a very poor random number generator: its parameters imply a recurrence period of 224, meaning that after less than 17 million calls RND will wrap around and start running through the exact same series of numbers all over again. RND should not be used for cryptography, scientific simulations or anything else remotely serious.
Errors
  • x has a string value: Type mismatch.

SCREEN (function)

value = SCREEN(row, column [, fn])

Returns the code point or colour attribute for the character at position row, col.

Parameters
  • row is a numeric expression in the range [1—25].
  • col is a numeric expression between 1 and the screen width (40 or 80).
  • fn is a numeric expression in [0—255]. If it is zero or not specified, the code point of the character is returned. If it is non-zero, in text mode the attribute is returned; in other screens, 0 is returned.
Errors
  • Any parameter has a string value: Type mismatch.
  • fn is not in [0—255]: Illegal function call.
  • fn is not in [-32768—32767]: Overflow.
  • row is not inside the current VIEW PRINT area: Illegal function call.
  • KEY ON and row=25: Illegal function call.
  • col is not in [1, width]: Illegal function call.
Notes
  • In GW-BASIC, the SCREEN function has anomalous error behaviour: constructions which for other functions would raise Syntax error or Missing operand instead raise Illegal function call. This behaviour is not replicated in PC-BASIC.

SGN

sign = SGN(number)

Returns the sign of number: 1 for positive, 0 for zero and -1 for negative.

Parameters
  • number is a numeric expression.
Errors
  • number has a string value: Type mismatch.

SIN

sine = SIN(angle)

Returns the sine of angle.

Parameters
  • angle is a numeric expression giving the angle in radians.
Notes
  • Unless PC-BASIC is run with the double option, this function returns a single-precision value.
  • The sine returned usually differs from the value returned by GW-BASIC in the least significant figure.
Errors
  • angle has a string value: Type mismatch.

SPACE$

spaces = SPACE$(number)

Returns a string of number spaces.

Parameters
  • number is a numeric expression in [0—255].
Errors
  • number has a string value: Type mismatch.
  • number is not in [-32768—32767]: Overflow.
  • number is not in [0—255]: Illegal function call.

SQR

root = SQR(number)

Returns the square root of number.

Parameters
  • number is a numeric expression.
Notes
  • Unless PC-BASIC is run with the double option, this function returns a single-precision value.
Errors
  • number has a string value: Type mismatch

STICK

pos = STICK(axis)

Returns a coordinate of a joystick axis. All coordinates returned are in the range [1—254] with 128 indicating the neutral position.

axis Return value
0 1st joystick x coordinate
1 1st joystick y coordinate
2 2nd joystick x coordinate
3 2nd joystick y coordinate
Parameters
  • axis is a numeric expression in [0—3] and indicates which axis to read.
Errors
  • axis has a string value: Type mismatch
  • axis is not in [-32768—32767]: Overflow.
  • axis is not in [0—3]: Illegal function call.

STR$

repr = STR$(number)

Returns the string representation of number.

Parameters
  • number is a numeric expression.
Errors
  • number has a string value: Type mismatch.

STRIG (function)

result = STRIG(mode)

Returns the status of the joystick trigger buttons. STRIG returns the following results, all Boolean values:

mode Return value
0 1st joystick, 1st trigger has been pressed since last poll.
1 1st joystick, 1st trigger is currently pressed.
2 2nd joystick, 1st trigger has been pressed since last poll.
3 2nd joystick, 1st trigger is currently pressed.
4 1st joystick, 2nd trigger has been pressed since last poll.
5 1st joystick, 2nd trigger is currently pressed.
6 2nd joystick, 2nd trigger has been pressed since last poll.
7 2nd joystick, 2nd trigger is currently pressed.
Parameters
  • mode is a numeric expression in [0—7].
Notes
  • The STRIG function returns correct results regardless of the STRIG ON status or whether STRIG(0) has been called first.
Errors
  • mode has a string value: Type mismatch.
  • mode is not in [-32768—32767]: Overflow.
  • mode is not in [0—7]: Illegal function call.

STRING$

string = STRING$(length, char)

Returns a string of length times character char.

Parameters
  • If char is a numeric expression, it must be in [0—255] and is interpreted as the code point of the character.
  • If char is a string expression, its first character is used.
Errors
  • length has a string value: Type mismatch.
  • char is the empty string: Illegal function call.
  • char or length is not in [-32768—32767]: Overflow.
  • char or length is not in [0—255]: Illegal function call.

TAN

tangent = TAN(angle)

Returns the tangent of angle.

Parameters
  • angle is a numeric expression giving the angle in radians.
Notes
  • Unless PC-BASIC is run with the double option, this function returns a single-precision value.
  • The tangent returned usually differs from the value returned by GW-BASIC in the least significant figure.
  • For angle close to multiples of π/2, the tangent is divergent or close to zero. The values returned will have very low precision in these cases.
Errors
  • angle has a string value: Type mismatch.

TIME$ (function)

time = TIME$

Returns the current BASIC time in the form "HH:mm:ss".

Notes
  • This function takes no arguments.

TIMER (function)

seconds = TIMER

Returns the number of seconds since midnight on the internal BASIC clock.

Notes
  • TIMER updates in ticks of 1/20 second.
  • The least-significant two bytes of TIMER are often used as a seed for the pseudorandom number generator through RANDOMIZE TIMER. Since these bytes only take values from a limited set, that's not in fact a particularly good random seed. However, the pseudorandom number generator included with GW-BASIC and PC-BASIC is so weak that it should not be used for anything serious anyway.
  • This function takes no arguments.

USR

value = USR[n](expr)

Raises Illegal function call.

Parameters
  • n is a digit [09].
  • expr is an expression.
Notes
  • In GW-BASIC, calls a machine-code function and returns its return value.
  • This function is not implemented in PC-BASIC.
Errors
  • n is not a digit [09]: Syntax error.

VAL

value = VAL(string)

Returns the numeric value of the string expression string. Parsing stops as soon as the first character is encountered that cannot be part of a number. If no characters are parsed, VAL returns zero. See the section on numeric literals for the recognised number formats.

Notes
  • Spaces before or even inside a number are ignored: VAL(" 1 0") returns 10.
  • If string contains one of the ASCII separator characters CHR$(28) (file separator), CHR$(29) (group separator) or CHR$(31) (unit separator), VAL returns zero. This is not the case with CHR$(30) (record separator). This behaviour conforms to GW-BASIC.
Errors
  • string has a number value: Type mismatch.

VARPTR

pointer = VARPTR({name|#file_num})

Returns the memory address of variable name or of the File Control Block of file number file_num.

Parameters
  • name is a previously defined variable or fully indexed array element.
  • file_num is a legal file number.
Notes
  • VARPTR can be used with PEEK to read a variable's internal representation.
Errors
  • name has not been previously defined: Illegal function call.
  • file_num has a string value: Type mismatch.
  • file_num is not in [1, max_files], where max_files is the maximum number of files as set by the max-files option: Bad file number.

VARPTR$

pointer = VARPTR$(name)

Returns the memory address of variable name in the form of a 3-byte string. The first byte is the length of the record the pointer points to:

2
for integers
3
for strings (length + pointer to string space)
4
for single-precision floats
8
for double-precision floats

The last two bytes are the pointer address (as returned by VARPTR) in little-endian order.

Errors
  • name has not been previously defined: Illegal function call.


Statements

A program line is composed of a line number and one or more statements. If multiple statements are put on one line, they must be separated by colons :. Statements may be empty. Each statement has its own idiosyncratic syntax.

Many reference works on GW-BASIC distinguish commands and statements; this distinction stems from the original Dartmouth design of the BASIC language, in which commands were not part of the language and could not be used in programs, but were rather used to control the interpreter itself. However, in GW-BASIC this distinction is less useful and therefore this reference includes what is traditionally thought of as commands in the category of statements.

AUTO

AUTO [line_number|.] [, [increment]]

Start automatic line numbering. Line numbers are automatically generated when Enter is pressed. If a program line exists at a generated line number, a * is shown after the line number. To avoid overwriting this line, leave it empty and press Enter. To stop automatic line numbering, press Ctrl+Break or Ctrl+C. The line being edited at that point is not saved. BASIC will return to command mode, even if AUTO was run from a program line.

Parameters
  • Line numbering starts at line_number, if specified. If . is specified, line numbering starts at the last program line that was stored. Otherwise, line numbering starts at 10.
  • Each next line number is incremented by increment, if specified. If a comma is used without specifying an increment, the last increment specified in an AUTO command is used. If not, increment defaults to 10.
Errors
  • line_number is not an unsigned-integer value in [0—65529]: Syntax error.
  • When automatic line numbering is enabled and Enter is pressed on an empty line with number larger than 65519: Undefined line number.
  • increment is 0: Illegal function call.

BEEP

BEEP

Beep the speaker at 800Hz for 0.25s.

Errors
  • If a Syntax error is raised, the beep is still produced.

BEEP (switch)

BEEP {ON|OFF}

Switches the internal speaker on or off.

Notes
  • Only legal with the syntax={pcjr|tandy} option.
  • On PC-BASIC, both the internal and the external speaker are emulated through the same sound system.

BLOAD

BLOAD file_spec [, offset]

Loads a memory image file into memory.

Parameters
  • The string expression file_spec is a valid file specification indicating the file to read the memory image from.
  • offset is a numeric expression in the range [-32768—65535]. It indicates an offset in the current DEF SEG segment where the file is to be stored. If not specified, the offset stored in the BSAVE file will be used. If negative, its two's complement will be used.
Errors
  • The loaded file is not in BSAVE format: Bad file mode.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).
  • file_spec has a numeric value: Type mismatch.
  • offset is not in the range [-32768—65535]: Overflow.

BSAVE

BSAVE file_spec, offset, length

Saves a region of memory to an image file.

Parameters
  • The string expression file_spec is a valid file specification indicating the file to write to.
  • offset is a numeric expression in the range [-32768—65535] indicating the offset into the current DEF SEG segment from where to start reading.
  • length is a numeric expression in the range [-32768—65535] indicating the number of bytes to read.
  • If offset or length are negative, their two's complement will be used.
Errors
  • file_spec has a numeric value: Type mismatch.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).
  • offset is not in the range [-32768—65535]: Overflow.
  • length is not in the range [-32768—65535]: Overflow.

CALL and CALLS

{CALL|CALLS} address_var [( p0 [, p1] ... )]

Does nothing.

Notes
  • In GW-BASIC, CALL or CALLS executes a machine language subroutine.
  • This statement is not implemented in PC-BASIC.
Parameters
  • address_var is a numeric variable name.
  • p0, p1, ... are variable names or array elements.
Errors
  • address_var is a string variable: Type mismatch.
  • address_var is a literal or expression: Syntax error.

CHAIN

CHAIN [MERGE] file_spec [, [line_number_expr] [, ALL] [, DELETE range [, ign]]]

Loads a program from file into memory and runs it, optionally transferring variables.

  • If ALL is specified, all variables are transferred. If not, the variables specified in a COMMON statement are transferred.
  • If MERGE is specified, the loaded program is merged into the existing program. To be able to use this, the program file indicated by file_spec must be in plain text format.
  • If DELETE is specified, the range of line numbers is deleted from the existing code before the merge. This is pointless without MERGE.
Parameters
  • The string expression file_spec is a valid file specification indicating the file to read the program from.
  • line_number_expr is a numeric expression. It will be interpreted as a line number in the new program and execution will start from this line number. If line_number_expr is negative, it will be interpreted as its two's-complement.
  • range is a line number range of which the closing line number is specified and exists before the merge.
  • ign is optional and ignored.
Notes
  • CHAIN preserves the OPTION BASE setting.
  • Only if ALL is specified, DEF FN definitions are preserved.
  • Only if MERGE is specified, DEFINT, DEFSTR, DEFSNG, DEFDBL definitions are preserved.
  • If specified, ALL must precede DELETE; if unspecified, no comma must be put in its place and only two commas should precede DELETE.
Errors
  • file_spec has a numeric value: Type mismatch.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).
  • The file specified in file_spec cannot be found: File not found.
  • MERGE is specified and the loaded program was not saved in plain-text mode: Bad file mode.
  • A line number in range is greater than 65529: Syntax error.
  • If a Syntax error is raised by CHAIN, no lines are deleted and the new program is not loaded.
  • The closing line number in range does not exist: Illegal function call
  • If line_number_expr does not evaluate to an existing line number in the new program, Illegal function call is raised but the load or merge is being performed.
  • A loaded text file contains lines without line numbers: Direct statement in file.
  • A loaded text file contains lines longer than 255 characters: Line buffer overflow. Attempting to load a text file that has LF rather than CR LF line endings may cause this error.

CHDIR

CHDIR dir_spec

Change the current directory on a disk device to dir_spec. Each disk device has its own current directory.

Parameters
  • The string expression dir_spec is a valid file specification indicating an existing directory on a disk device.
Errors
  • No matching path is found: Path not found.
  • dir_spec has a numeric value: Type mismatch.
  • dir_spec is empty: Bad file name.

CIRCLE

CIRCLE [STEP] (x, y), radius [, [colour] [, [start] [, [end] [, aspect]]]

Draw an ellipse or ellipse sector.

Parameters
  • The midpoint of the ellipse is at (x,y). If STEP is specified, the midpoint is (x,y) away from the current position.
  • radius is the radius, in pixels, along the long axis.
  • colour is the colour attribute.
  • If start and end are specified, a sector of the ellipse is drawn from start radians to end radians, with zero radians the intersection with the right-hand x axis. If a negative value is specified, the arc sector is connected by a line to the midpoint.
  • aspect specifies the ratio between the y radius and the x radius. If it is not specified, the standard value for the SCREEN mode is used (see there), so as to make the ellipse appear like a circle on the original hardware.
Notes
  • For aspect <> 1, the midpoint algorithm used does not pixel-perfectly reproduce GW-BASIC's ellipses.
Errors
  • The statement is executed in text mode: Illegal function call.
  • start or end is not in [0—2π]: Illegal function call.
  • The statement ends with a comma: Missing operand.

CLEAR

CLEAR [expr] [, [mem_limit] [, [stack_size] [, video_memory]]]

Clears all variables, arrays,DEF FN user functions and DEFtype type definitions. Closes all files. Turns off all sound. Resets PLAY state and sets music to foreground. Clears all ON ERROR traps. Resets ERR and ERL to zero. Disables all events. Turns PEN and STRIG off. Resets the random number generator. Clears the loop stack. Resets the DRAW state and the current graphics position.

Parameters
  • mem_limit specifies the upper limit of usable memory. Default is previous memory size. Default memory size is 65534.
  • stack_size specifies the amount of memory available to the BASIC stack. Default is previous stack size. Default stack size is 512.
  • video_memory specifies the amount of memory available to the video adapter. This parameter is only legal with one of the options syntax={pcjr, tandy}. Instead of using CLEAR, the option video-memory can also be used to set video memory size.
Notes
  • The purpose of expr is unknown.
  • If called inside a FORNEXT or WHILEWEND loop, an error will be raised at the NEXT or WEND statement, since the loop stacks have been cleared.
Errors
  • Any of the arguments has a string value: Type mismatch.
  • mem_limit, stack_size are not in [-32768—65535]: Overflow.
  • mem_limit or stack_size equal 0: Illegal function call.
  • mem_limit equals -1 or 65535: Out of memory.
  • mem_limit or expr are too low: Out of memory.
  • expr is not in [-32768—32767]: Overflow.
  • expr is negative: Illegal function call.

CLOSE

CLOSE [[#] file_0 [, [#] file_1] ...]

Closes files. If no file numbers are specified, all open files are closed. The hash (#) is optional and has no effect.

Parameters
  • file_1, file_2, ... are numeric expressions yielding file numbers.
Notes
  • No error is raised if the specified file numbers were not open.
Errors
  • file_1, file_2, ... are not in [-32768—32767]: Overflow.
  • file_1, file_2, ... are not in [0—255]: Illegal function call.
  • file_1, file_2, ... have a string value: Type mismatch.
  • The statement ends in a comma, Missing operand.
  • If an error occurs, only the files before the erratic value are closed.

CLS

CLS [x][,]

Clears the screen or part of it. If x is not specified, in SCREEN 0 the text view region is cleared; in other screens, the graphics view region is cleared. The comma is optional and has no effect.

Parameters

x is a numeric valued expression.

  • If x = 0, the whole screen is cleared.
  • If x = 1, the graphics view region is cleared.
  • If x = 2, the text view region is cleared.

The optional argument x is not available with syntax={pcjr|tandy}.

Errors
  • x is has a string value: Type mismatch.
  • x is not in [-32768—32767]: Overflow .
  • x is not in [0, 1, 2]: Illegal function call.
  • No comma is specified but more text follows: Illegal function call.
  • A comma is specified followed by more: Syntax error.
  • syntax=pcjr is set and an argument is specified: Syntax error.
  • syntax=tandy is set and an argument is specified: Illegal function call.
  • If an error occurs, the screen is not cleared.

COLOR (text mode)

COLOR [foreground] [, [background] [, border]]

Changes the current foreground and background attributes. All new characters printed will take the newly set attributes. Existing characters on the screen are not affected.

Parameters
  • foreground is a numeric expression in [0—31]. This specifies the new foreground attribute. Attributes 16—31 are blinking versions of attributes 0—15.
  • background is a numeric expression in [0—15]. This specifies the new background attribute. It is taken MOD 8: Values 8—15 produce the same colour as 0—7.
  • border is a numeric expression in [0—15] specifying the border attribute.
Textmode attributes (colour)
Background attribute
0 1 2 3 4 5 6 7
FG 0 00 XX 10 XX 20 XX 30 XX 40 XX 50 XX 60 XX 70 XX
1 01 XX 11 XX 21 XX 31 XX 41 XX 51 XX 61 XX 71 XX
2 02 XX 12 XX 22 XX 32 XX 42 XX 52 XX 62 XX 72 XX
3 03 XX 13 XX 23 XX 33 XX 43 XX 53 XX 63 XX 73 XX
4 04 XX 14 XX 24 XX 34 XX 44 XX 54 XX 64 XX 74 XX
5 05 XX 15 XX 25 XX 35 XX 45 XX 55 XX 65 XX 75 XX
6 06 XX 16 XX 26 XX 36 XX 46 XX 56 XX 66 XX 76 XX
7 07 XX 17 XX 27 XX 37 XX 47 XX 57 XX 67 XX 77 XX
8 08 XX 18 XX 28 XX 38 XX 48 XX 58 XX 68 XX 78 XX
9 09 XX 19 XX 29 XX 39 XX 49 XX 59 XX 69 XX 79 XX
10 0a XX 1a XX 2a XX 3a XX 4a XX 5a XX 6a XX 7a XX
11 0b XX 1b XX 2b XX 3b XX 4b XX 5b XX 6b XX 7b XX
12 0c XX 1c XX 2c XX 3c XX 4c XX 5c XX 6c XX 7c XX
13 0d XX 1d XX 2d XX 3d XX 4d XX 5d XX 6d XX 7d XX
14 0e XX 1e XX 2e XX 3e XX 4e XX 5e XX 6e XX 7e XX
15 0f XX 1f XX 2f XX 3f XX 4f XX 5f XX 6f XX 7f XX
16 80 XX 90 XX a0 XX b0 XX c0 XX d0 XX e0 XX f0 XX
17 81 XX 91 XX a1 XX b1 XX c1 XX d1 XX e1 XX f1 XX
18 82 XX 92 XX a2 XX b2 XX c2 XX d2 XX e2 XX f2 XX
19 83 XX 93 XX a3 XX b3 XX c3 XX d3 XX e3 XX f3 XX
20 84 XX 94 XX a4 XX b4 XX c4 XX d4 XX e4 XX f4 XX
21 85 XX 95 XX a5 XX b5 XX c5 XX d5 XX e5 XX f5 XX
22 86 XX 96 XX a6 XX b6 XX c6 XX d6 XX e6 XX f6 XX
23 87 XX 97 XX a7 XX b7 XX c7 XX d7 XX e7 XX f7 XX
24 88 XX 98 XX a8 XX b8 XX c8 XX d8 XX e8 XX f8 XX
25 89 XX 99 XX a9 XX b9 XX c9 XX d9 XX e9 XX f9 XX
26 8a XX 9a XX aa XX ba XX ca XX da XX ea XX fa XX
27 8b XX 9b XX ab XX bb XX cb XX db XX eb XX fb XX
28 8c XX 9c XX ac XX bc XX cc XX dc XX ec XX fc XX
29 8d XX 9d XX ad XX bd XX cd XX dd XX ed XX fd XX
30 8e XX 9e XX ae XX be XX ce XX de XX ee XX fe XX
31 8f XX 9f XX af XX bf XX cf XX df XX ef XX ff XX
Textmode attributes (monochrome)
Background attribute
0 1 2 3 4 5 6 7
FG 0 00 XX 10 XX 20 XX 30 XX 40 XX 50 XX 60 XX 70 XX
1 01 XX 11 XX 21 XX 31 XX 41 XX 51 XX 61 XX 71 XX
2 02 XX 12 XX 22 XX 32 XX 42 XX 52 XX 62 XX 72 XX
3 03 XX 13 XX 23 XX 33 XX 43 XX 53 XX 63 XX 73 XX
4 04 XX 14 XX 24 XX 34 XX 44 XX 54 XX 64 XX 74 XX
5 05 XX 15 XX 25 XX 35 XX 45 XX 55 XX 65 XX 75 XX
6 06 XX 16 XX 26 XX 36 XX 46 XX 56 XX 66 XX 76 XX
7 07 XX 17 XX 27 XX 37 XX 47 XX 57 XX 67 XX 77 XX
8 08 XX 18 XX 28 XX 38 XX 48 XX 58 XX 68 XX 78 XX
9 09 XX 19 XX 29 XX 39 XX 49 XX 59 XX 69 XX 79 XX
10 0a XX 1a XX 2a XX 3a XX 4a XX 5a XX 6a XX 7a XX
11 0b XX 1b XX 2b XX 3b XX 4b XX 5b XX 6b XX 7b XX
12 0c XX 1c XX 2c XX 3c XX 4c XX 5c XX 6c XX 7c XX
13 0d XX 1d XX 2d XX 3d XX 4d XX 5d XX 6d XX 7d XX
14 0e XX 1e XX 2e XX 3e XX 4e XX 5e XX 6e XX 7e XX
15 0f XX 1f XX 2f XX 3f XX 4f XX 5f XX 6f XX 7f XX
16 80 XX 90 XX a0 XX b0 XX c0 XX d0 XX e0 XX f0 XX
17 81 XX 91 XX a1 XX b1 XX c1 XX d1 XX e1 XX f1 XX
18 82 XX 92 XX a2 XX b2 XX c2 XX d2 XX e2 XX f2 XX
19 83 XX 93 XX a3 XX b3 XX c3 XX d3 XX e3 XX f3 XX
20 84 XX 94 XX a4 XX b4 XX c4 XX d4 XX e4 XX f4 XX
21 85 XX 95 XX a5 XX b5 XX c5 XX d5 XX e5 XX f5 XX
22 86 XX 96 XX a6 XX b6 XX c6 XX d6 XX e6 XX f6 XX
23 87 XX 97 XX a7 XX b7 XX c7 XX d7 XX e7 XX f7 XX
24 88 XX 98 XX a8 XX b8 XX c8 XX d8 XX e8 XX f8 XX
25 89 XX 99 XX a9 XX b9 XX c9 XX d9 XX e9 XX f9 XX
26 8a XX 9a XX aa XX ba XX ca XX da XX ea XX fa XX
27 8b XX 9b XX ab XX bb XX cb XX db XX eb XX fb XX
28 8c XX 9c XX ac XX bc XX cc XX dc XX ec XX fc XX
29 8d XX 9d XX ad XX bd XX cd XX dd XX ed XX fd XX
30 8e XX 9e XX ae XX be XX ce XX de XX ee XX fe XX
31 8f XX 9f XX af XX bf XX cf XX df XX ef XX ff XX
Notes
Errors
  • Any of the parameters has a string value: Type mismatch.
  • Any of the parameters is not in [-32768—32767]: Overflow.
  • foreground is not in [0—31], background is not in [0—15] or border is not in [0—15]: Illegal function call.
  • Statement is used in SCREEN 2: Illegal function call.

COLOR (SCREEN 1)

COLOR [palette_0] [, palette [, override]]

Assigns new colours to the palette of attributes.

  • palette_0 is a numeric expression in [0—255]. This sets the palette colour associated with attribute 0; by default, the background has this attribute. All pixels with this attribute will change colour. The palette colour value is taken from the 64-colour set. palette_0 is taken MOD 64.
  • palette is a numeric expression in [0—255] that specifies the palette:
    • palette odd sets the standard CGA palette (cyan, magenta, grey).
    • palette even sets the alternative palette (green, red, brown).
    All pixels with attributes 1,2,3 will change colour to the new palette.
  • override is a numeric expression in [0—255]. If override is specified, palette is set as above but using override instead of palette. palette is then ignored.
CGA palettes
Attribute Palette 0 Palette 1 Alternate palette
ColourLoHi ColourLoHi ColourLoHi
0 Black Black Black
1 Green Cyan Cyan
2 Red Magenta Red
3 Brown White White
Notes
Errors
  • Any of the parameters has a string value: Type mismatch.
  • Any of the parameters is not in [-32768—32767]: Overflow.
  • Any of the parameters is not in [0—255]: Illegal function call.

COLOR (SCREEN 3—9)

COLOR [foreground] [, palette_0 [, dummy]]

Changes the current foreground attribute and the colour for attribute 0.

Parameters
  • foreground is a numeric expression in [1—15] This sets the new foreground attribute. This applies only to new characters printed or pixels plotted.
  • palette_0 is a numeric expression in [0—15] This sets the colour associated with attribute 0; by default, the background has this attribute. All pixels with this attribute will change colour. In SCREEN 7 and 8, the palette_0 colour is taken from the first 8 of the 16-colour EGA set. palette_0 is taken MOD 8. IN SCREEN 9, the colour value is taken from the 64-colour set.
  • dummy is a numeric expression with a value in [0—255] The value of dummy is ignored.
EGA default palette
AttributeColour
0Black
1Blue
2Green
3Cyan
4Red
5Magenta
6Brown
7Low-intensity white
8Grey
9Light Blue
10Light Green
11Light Cyan
12Light Red
13Light Magenta
14Light Yellow
15High-intensity white
EGA colour list
0 8 16 24 32 40 48 56
1 9 17 25 33 41 49 57
2 10 18 26 34 42 50 58
3 11 19 27 35 43 51 59
4 12 20 28 36 44 52 60
5 13 21 29 37 45 53 61
6 14 22 30 38 46 54 62
7 15 23 31 39 47 55 63
Notes
Errors
  • Any of the parameters has a string value: Type mismatch.
  • Any of the parameters is not in [-32768—32767]: Overflow.
  • foreground is not in [1—15]; background is not in [0—15]; or dummy is not in [0—255]: Illegal function call.

COM

COM(port) {ON|OFF|STOP}
  • ON: enables ON COM(port) event trapping of the emulated serial port.
  • OFF: disables trapping.
  • STOP: halts trapping until COM(port) ON is used. Events that occur while trapping is halted will trigger immediately when trapping is re-enabled.
Parameters
  • port is a numeric expression with a value of 1 or 2. This specifies which serial port (COM1: or COM2:) is trapped. If port equals 0, this statement does nothing.
Errors
  • port a string value: Type mismatch.
  • port is not in [-32768—32767]: Overflow.
  • port is not in [0—3]: Illegal function call.

COMMON

COMMON [var_0 [( [index_0] )] [, [var_1 [( [index_1] )] ]] ...]

Specifies variables to be passed as common variables to the program called with CHAIN.

Parameters
  • var_0, var_1, ... are names of scalar or array variables.
  • index_0, index_1, ... are optional number literals; they are ignored.
Notes
  • Array elements with square brackets and an index do not cause an error, but are ignored.
  • COMMON statements are not executed during run time; rather, when a CHAIN command is encountered where ALL is not specified, all COMMON declarations in the program are parsed. As a consequence, the DEFSTR, DEFINT, DEFSNG or DEFDBL settings used are those that are active at the time of execution of the CHAIN statement.
  • COMMON declarations need not be reachable in the program flow in order to be used. They may occur anywhere before or after the CHAIN statement that uses them.
  • Variables may be repeated or occur in multiple COMMON declarations.
  • If the COMMON keyword is not the first element of the statement, the declaration will be ignored. In particular, any COMMON declaration that occurs directly after a THEN or ELSE keyword will not be used. COMMON in the second or later statements of a compound statement after THEN or ELSE will be used regardless of the value of the IF condition.

CONT

CONT [anything]

Resumes execution of a program that has been halted by STOP, END, Ctrl+C, or Ctrl+Break.

Notes
  • Anything after the CONT keyword is ignored.
  • This statement can only be used in direct mode.
  • If a break is encountered in GOSUB routine called from a continuing direct line (e.g. GOSUB 100:PRINT A$), CONT will overwrite the running direct line. As the subroutine RETURNs to the position after the GOSUB in the old direct line, strange things may happen if commands are given after CONT. In GW-BASIC, this can lead to strange errors in non-existing program lines as the parser executes bytes that are not part of a program line. In PC-BASIC, if the new direct line is shorter, execution stops after RETURN; but if the direct line is extended beyond the old return position, the parser tries to resume at that return position, with strange effects.
Errors
  • No program is loaded, a program has not been run, after a program line has been modified or after CLEAR: Can't continue.
  • The break occurred in a direct line: Can't continue.
  • CONT is used in a program: Can't continue.

DATA

DATA [const_0] [, [const_1]] ...

Specifies data that can be read by a READ statement.

Parameters
  • const_0, const_1, ... are string and number literals or may be empty. String literals can be given with or without quotation marks. If quotation marks are omitted, leading and trailing whitespace is ignored and commas or colons will terminate the data statement.
Notes
  • DATA declarations need not be reachable in the program flow in order to be used. They may occur anywhere before or after the READ statement that uses them.
  • If the DATA keyword is not the first element of the statement, the declaration will be ignored. In particular, any DATA declaration that occurs directly after a THEN or ELSE keyword will not be used. DATA in the second or later statements of a compound statement after THEN or ELSE will be used regardless of the value of the IF condition.
Errors
  • If the type of the literal does not match that of the corresponding READ statement, a Syntax error occurs on the DATA statement.

DATE$ (statement)

DATE$ = date

Sets the system date. date is a string expression that represents a date in one of the formats: "mm{-|/}dd{-|/}yy" or "mm{-|/}dd{-|/}yyyy"

Of these,

  • mm may be one or two characters long and must be in [1—12].
  • dd may be one or two characters long and must be in [1—31].
  • yyyy must be in [1980—2099].
  • yy may be one or two characters long and must be in one of the ranges:
    • [0—77], interpreted as 2000—2077; or
    • [80—99], interpreted as 1980—1999.
Notes
  • The system date is not actually changed; rather, PC-BASIC remembers the offset from the true system date. This avoids requiring user permission to change the system time.
  • GW-BASIC appears to accept invalid dates such as "02-31-2000". PC-BASIC raises Illegal function call for these.
Errors
  • date has a numeric value: Type mismatch.
  • date is not in the format specified above: Illegal function call.

DEF FN

DEF FN[ ]name [(arg_0 [, arg_1] ...)] = expression

Defines a function called FNname (or FN name: spaces between FN and name are optional). On calling FNname( ... ), expression is evaluated with the supplied parameters substituted. Any variable names used in the function that are not in the argument list refer to the corresponding global variables. The result of the evaluation is the return value of FNname. The type of the return value must be compatible with the type indicated by name.

Notes
  • This statement may only be used on a program line.
  • As the function must be a single expression and PC-BASIC does not have a ternary operator, there is no way to define a recursive function that actually terminates.
Parameters
  • name must be a legal variable name.
  • arg_0, arg_1, ... must be legal variable names. These are the parameters of the function. Variables of the same name may or may not exist in the program; their value is not affected or used by the defined function.
  • expression must be a legal PC-BASIC expression.
Errors
  • The statement is executed directly instead of in a program line: Illegal direct.
  • If the type of the return value is incompatible with the type of name, no error is raised at the DEF FN statement; however, a Type mismatch will be raised at the first call of FNname.

DEFINT, DEFDBL, DEFSNG, DEFSTR

{DEFINT|DEFDBL|DEFSNG|DEFSTR} first_0[- last_0] [, first_1[- last_1]] ...

Sets the type that is assumed if no sigil is specified when a variable name is used. The statement sets the default type for variables starting with a letter from the ranges specified.

The default type is set to:

DEFINT
integer (%)
DEFDBL
double (#)
DEFSNG
single (!)
DEFSTR
string ($)
Parameters
  • first_0, last_0, ... are letters of the alphabet. Pairs of letters connected by a dash - indicate inclusive ranges.
Notes
  • DEFSNG A-Z is the default setting.

DEF SEG

DEF SEG [= address]

Sets the memory segment to be used by BLOAD, BSAVE, CALL, PEEK, POKE, and USR.

Parameters
  • address is a numeric expression in [-32768—65535].
Notes
  • If address is negative, it is interpreted as its two's complement.
  • If address is not specified, the segment is set to the GW-BASIC data segment.
Errors
  • address has a string value: Type mismatch.
  • address is not in [-32768—65535]: Overflow.

DEF USR

DEF USR[n] = address

Does nothing.

Parameters
  • n is a digit between 0 and 9 inclusive.
  • address is a numeric expression in [-32768—65535].
Notes
  • In GW-BASIC, this statement sets the starting address of an assembly-language function.
  • This statement is not implemented in PC-BASIC.
  • If address is negative, it is interpreted as its two's complement.
Errors
  • n is not a digit in [0—9]: Syntax error.
  • address has a string value: Type mismatch.
  • address is not in [-32768—65535]: Overflow.

DELETE

DELETE [line_number_0|.] [-[line_number_1|.] ]

Deletes a range of lines from the program. Also stops program execution and returns control to the user.

Parameters
  • line_number_0 and line_number_1 are line numbers in the range [0—65529], specifying the inclusive range of line numbers to delete.
  • A . indicates the last line edited.
  • If the start point is omitted, the range will start at the start of the program.
  • If the end point is omitted, the range will end at the end of the program.
  • If no range is specified, the whole program will be deleted.
Errors
  • line_number_0 or line_number_1 is greater than 65529: Syntax error.
  • The range specified does not include any program lines stored: Illegal function call.

DIM

DIM name [{(|[} limit_0 [, limit_1] ... {)|]}] [, ... ]

Allocates memory for one or more arrays. The DIM statement also fixes the number of indices of the array. An array can only be allocated once; to re-allocate an array, ERASE or CLEAR must be executed first. If an array is first used without a DIM statement, it is automatically allocated with its maximum indices set at 10 for each index position used. A DIM entry with no brackets and no indices performs no operation. Empty brackets are not allowed. The least index allowed is determined by OPTION BASE.

Parameters
  • name, ... are legal variable names specifying the arrays to be allocated.
  • limit_0, limit_1, ... are numeric expressions that specify the greatest index allowed at that position.
Notes
  • Mixed brackets are allowed.
  • The size of arrays is limited by the available BASIC memory.
  • The maximum number of indices is, theoretically, 255. In practice, it is limited by the 255-byte limit on the length of program lines.
Errors
  • name has already been dimensioned: Duplicate definition.
  • An index is empty: Syntax error.
  • An index is missing at the end: Missing operand.
  • limit_0, limit_1, ... have a string value: Type mismatch.
  • limit_0, limit_1, ... are not within [-32768—32767]: Overflow.
  • limit_0, limit_1, ... are negative: Illegal function call.
  • The array exceeds the size of available variable space: Out of memory.

DRAW

DRAW gml_string

Draws the shape specified by gml_string, a string expression in Graphics Macro Language (GML).

Graphics Macro Language reference
Movement commands
[B][N] movement where the default is to move and draw; the optional prefixes mean:
B move but do not plot
N return to original point after move
and movement is one of:
U[n] up n steps
L[n] left n steps
D[n] down n steps
R[n] right n steps
E[n] up and right n steps
F[n] down and right n steps
G[n] down and left n steps
H[n] up and left n steps
M{+|-}x,[+|-]y move (x,y) steps
Mx,y move to view region coordinate (x,y)

where n is an integer in [-32768—32767] and x, y are integers in [0—9999]. Where optional, n defaults to 1.

Scale commands
Sn set the step size to n/4. The default step size is 1 pixel. n is an integer in [1—255]
TAn set the angle to n degrees. The default angle is 0 degrees. n is an integer in [-360—360]
An set the angle to 0 for n=0, 90 for n=1, 180 for n=2, 270 for n=3. n is an integer in [0—3]
Colour commands
Cn set the foreground attribute to n, where n is an integer in [-32768—32767] See COLOR.
Pn,b flood fill with attribute n and boundary attribute b, where n, b are integers in [0—9999] See PAINT.
Subroutine command
Xs execute a substring

s is one of the following:

  • a string variable name followed by semicolon (;)
  • the result of VARPTR$() on a string variable

Numeric variables n, x, y, b in the commands above can be:

  • an integer literal, e.g. DRAW "U100"
  • a numeric variable name or array element var preceded by = and followed by ;. For example, DRAW "U=VAR;" or DRAW "U=A(1);"
  • the result of VARPTR$(var) preceded by =. For example, DRAW "U=" + VARPTR$(VAR)
Notes
  • The CLS statement resets the step size to 1 pixel, angle to 0 degrees and position to the centre of the view region.
  • The value n in the TA, A and C command can be left out but only if the command is terminated by a semicolon. n defaults to 0.
  • In GW-BASIC, the numeric arguments of U, L, D, R, E, F, G, H, and C can be in the range [-99999—99999]; however, results for large numbers are unpredictable. This is not implemented in PC-BASIC.
Errors
  • gml_string has a numeric value: Type mismatch.
  • gml_string has errors in the GML: Illegal function call.
  • A variable referenced in the GML string is of incorrect type: Type mismatch.

EDIT

EDIT {line_number|.}

Displays the specified program line with the cursor positioned for editing. line_number must be a line that exists in the program, or a period (.) to indicate the last line stored.

Errors
  • No line_number is specified: Undefined line number.
  • More characters are written after the line number: Illegal function call.
  • line_number is not in [0—65529]: Illegal function call.
  • The specified line number does not exist: Undefined line number.

ELSE

ELSE [anything]

Unless part of an IF statement on the same line, anything after ELSE is ignored in the same way as after ' or :REM. No colon : preceding the ELSE statement is necessary. See IF for normal usage.


END

END

Closes all files, stops program execution and returns control to the user. No message is printed. It is possible to resume execution at the next statement using CONT.


ENVIRON

ENVIRON command_string

Sets a shell environment variable.

Parameters

command_string is a string expression of one of the following forms:

"VARIABLE=VALUE"
to set VARIABLE to VALUE;
"VARIABLE="
to unset VARIABLE.

VARIABLE must be an ASCII string and will be converted to uppercase on case-sensitive systems.

Errors
  • command_string has a numeric value: Type mismatch.
  • command_string is not of the required form: Illegal function call.
  • VARIABLE contains characters outside of ASCII: Illegal function call.

ERASE

ERASE array_0 [, array_1] ...

De-allocates arrays. The data stored in the arrays is lost.

Parameters
  • array_0, array_1 ... are names of existing arrays. The names must be specified without brackets.
Errors
  • No array names are given: Syntax error.
  • array_0, array_1 ... do not exist: Illegal function call.
  • If an error occurs, the arrays named before the error occurred are erased.

ERROR

ERROR error_number

Raises the error with number error_number.

Parameters
  • error_number is an expression with a numeric value.
Errors
  • error_number has a string value: Type mismatch.
  • error_number is not in [-32768—32767]: Overflow.
  • error_number is not in [1—255]: Illegal function call.

FIELD

FIELD [#] file_number [, width_0 AS name_0 [, width_1 AS name_1] ...]

Assigns variables to the random-access record buffer. The record buffer is a region of memory of length defined by the OPEN statement; the default record length is 128 bytes. The FIELD statement assigns a portion of this region to one or more fixed-length string variables, so that the value of these strings is whatever happens to be in the record buffer at that location.

Notes
  • A FIELD statement without any variables specified has no effect.
  • Another FIELD statement on the same file will specify an alternative mapping of the same file buffer; all mappings will be in effect simultaneously.
  • A subsequent assignment or LET or MID$ statement on name_0 , name_1 ... will dis- associate the string variable from the field buffer.
  • Use LSET, RSET or MID$ to copy values into a FIELD buffer.
  • Use GET to read values from the file into the field buffer, changing the variables.
  • Use PUT to write the field buffer to the file.
Parameters
  • file_number is a numeric expression that yields the number of an open random-access file. The # is optional and has no effect.
  • width_0, width_1, ... are numeric expressions giving the length of the string variables
  • name_0 , name_1 ... are string variables.
Errors
  • file_number is not in [0—255]: Illegal function call.
  • file_number is not the number of an open file: Bad file number.
  • file_number is open under a mode other than RANDOM: Bad file mode.
  • The statement ends in a comma: Missing operand.
  • No file number is specified: Missing operand.
  • The lengths in a FIELD statement add up to a number larger than the record length of the field buffer: Field overflow.
  • name_0 , name_1 ... specify a non-string variable: Type mismatch.

FILES

FILES [filter_spec]

Displays the files fitting the specified filter in the specified directory on a disk device. If filter_spec is not specified, displays all files in the current working directory.

Parameters
  • filter_spec is a string expression that is much like a file specification, but optionally allows the file name part to contain wildcards.
Notes
  • The filename filter may contain the following wildcards:
    ? Matches any legal file name character.
    * Matches any series of legal file name characters.
  • The filter will only match MS-DOS style filenames.
  • Matched character series do not stretch across directory separators \ or extension separators .. To match all files with all extensions, use *.*.
  • Alternatively, if all files in a specified directory are required, end the directory name with a backslash \.
Errors
  • filter_spec has a numeric value: Type mismatch.
  • filter_spec is the empty string: Bad file name.
  • The specified filter does not match any files: File not found.

FOR

FOR loop_var = start TO stop [STEP step]

Initiates a FOR—NEXT loop.

Initially, loop_var is set to start. Then, the statements between the FOR statement and the NEXT statement are executed and loop_var is incremented by step (if step is not specified, by 1). This is repeated until loop_var has become greater than stop. Execution then continues at the statement following NEXT. The value of loop_var equals stop+step after the loop.

start, stop and step are evaluated only once and the resulting values are used throughout the loop.

Parameters
  • loop_var is an integer or single-precision variable.
  • start, stop and step are numeric expressions.
Errors
  • No NEXT statement is found to match the FOR statement: FOR without NEXT occurs at the FOR statement.
  • loop_var is a string variable or start, stop, or end has a string value: Type mismatch.
  • loop_var is a double-precision variable: Type mismatch.
  • loop_var is an array element: Syntax error .
  • loop_var is an integer variable and a start, stop or step is outside the range [-32768, 32767]: Overflow .

GET (files)

GET [#] file_number [, record_number]

Read a record from the random-access file file_number at position record_number. The record can be accessed through the FIELD variables or through INPUT$, INPUT or LINE INPUT.

Parameters
  • file_number is a numeric expression that yields the number of an open random-access file. The # is optional and has no effect.
  • record_number is a numeric expression in [1—33554432] (2^25), and is interpreted as the record number.
Notes
  • If the record number is beyond the end of the file, the file buffer is filled with null bytes.
  • The record number is stored as single-precision; this precision is not high enough to distinguish single records near the maximum value of 2^25.
Errors
  • record_number is not in [1—33554432]: Bad record number.
  • file_number is not in [0—255]: Illegal function call.
  • file_number is not the number of an open file: Bad file mode.
  • file_number is open under a mode other than RANDOM: Bad file mode.
  • file_number is not specified: Missing operand.

GET (communications)

GET [#] com_file_number [, number_bytes]

Read number_bytes bytes from the communications buffer opened under file number com_file_number. The record can be accessed through the FIELD variables or through INPUT$, INPUT or LINE INPUT.

Parameters
  • file_number is a numeric expression that yields the number of a file open to a COM device. The # is optional and has no effect.
  • number_bytes is a numeric expression between 1 and the COM buffer length, inclusive.
Notes
  • If bytes is 32768 or greater, GW-BASIC hangs. This functionality is not implemented in PC-BASIC.
  • In GW-BASIC, Device I/O error is raised for overrun error, framing error, and break interrupt. Device fault is raised if DSR is lost during I/O. Parity error is raised if parity is enabled and incorrect parity is encountered. This is according to the manual; it is untested.
Errors
  • bytes is less than 1: Bad record number
  • bytes is less than 32768 and greater than the COM buffer length: Illegal function call.
  • com_file_number is not specified: Missing operand.
  • com_file_number is not in [0—255]: Illegal function call.
  • com_file_number is not the number of an open file: Bad file number.
  • If the serial input buffer is full, i.e. LOF(com_file_number) = 0, and LOC(com_file_number) = 255: Communication buffer overflow
  • If the carrier drops during GET, hangs until the Ctrl+Break key is pressed.

GET (graphics)

GET (x0, y0) - [STEP] (x1, y1), array_name

Stores a rectangular area of the graphics screen in an array. The area stored is a rectangle parallel to the screen edges, bounded by the top-left and bottom-right coordinates x0,y0 and x1,y1. If STEP is specified, x1,y1 is an offset from x0,y0. The area is such that these corner points are inside it.

The image stored in the array can then be put on the screen using PUT. For the purposes of GET, any array is considered a string of bytes. The byte size of an array can be calculated as number_elements * byte_size with byte_size equal to 2 for integers (%), 4 for single (!) and 8 for double (#). Array byte size for string is 3, but string arrays are not allowed in GET. For calculating the number of elements, keep in mind that OPTION BASE 0 is the default; in which case an array with maximum index 10 has 11 elements. This works through in multidimensional arrays.

The array format is as follows:

Byte Contains
0, 1 Number of x pixels, unsigned int. In SCREEN 1, this value is doubled.
2, 3 Number of y pixels, unsigned int.
4— Pixel data. Data is arranged in 2-byte words. The first 16-bit word holds the bit 0 of the first 16 pixels on the top row. The second word holds the second bit, etc. Data is word-aligned at the end of each row. Thus, in a screen mode with 4 bits per pixel, the first row takes at least 8 bytes (4 words), even if it consists of only one pixel. The number of bits per pixel depends on the SCREEN mode.
Parameters
  • array_name is the name of a numeric array dimensioned with enough space to store the area.
  • x0, y0, x1, y1 are numeric expressions.
Notes
  • In PCjr/Tandy mode, in SCREEN 6, GET stores an area of twice the width of the specified rectangle.
Errors
  • The array does not exist: Illegal function call.
  • array_name refers to a string array: Type mismatch.
  • The area is too large for the array: Illegal function call.
  • x0, ... y1 are string expressions: Type mismatch.
  • x0, ... y1 are not in [-32768—32767]: Overflow.
  • x0, ... y1 are outside the current VIEW or WINDOW: Illegal function call

GOSUB

GO[ ]SUB line_number [anything]

Jumps to a subroutine at line_number. The next RETURN statement jumps back to the statement after GOSUB. Anything after line_number until the end of the statement is ignored. If executed from a direct line, GOSUB runs the subroutine and the following RETURN returns execution to the direct line.

Parameters
  • line_number is an existing line number literal.
  • Further characters on the line are ignored until end of statement.
Notes
  • If no RETURN is encountered, no problem.
  • One optional space is allowed between GO and SUB; it will not be retained in the program.
Errors
  • If line_number does not exist: Undefined line number.
  • If line_number is greater than 65529, only the first 4 characters are read (e.g. 6553)

GOTO

GO[ ]TO line_number [anything]

Jumps to line_number. Anything after line_number until the end of the statement is ignored. If executed from a direct line, GOTO starts execution of the program at the specified line.

Parameters
  • line_number is an existing line number literal.
  • Further characters on the line are ignored until end of statement.
Notes
  • Any number of optional spaces is allowed between GO and TO, but they will not be retained in the program.
  • If line_number is greater than 65529, only the first 4 characters are read (e.g. GOTO 65530 is executed as GOTO 6553)
Errors
  • line_number does not exist: Undefined line number.

IF

IF truth_value [,] {THEN|GOTO} [compound_statement_true|line_number_true [anything]] [ELSE [compound_statement_false|line_number_false [anything]]]

If truth_value is non-zero, executes compound_statement_true or jumps to line_number_true . If it is zero, executes compound_statement_false or jumps to line_number_false .

Parameters
  • truth_value is a numeric expression.
  • line_number_false and line_number_true are existing line numbers.
  • compound_statement_false and compound_statement_true are compound statements, consisting of at least one statement, optionally followed by further statements separated by colons :. The compound statements may contain nested IF—THEN—ELSE statements.
Notes
  • The comma is optional and ignored.
  • ELSE clauses are optional; they are bound to the innermost free IF statement if nested. Additional ELSE clauses that have no matching IF are ignored.
  • All clauses must be on the same program line.
  • THEN and GOTO are interchangeable; which one is chosen is independent of whether a statement or a line number is given. GOTO PRINT 1 is fine.
  • As in GOTO, anything after the line number is ignored.
Errors
  • If truth_value has a string value: Type mismatch.
  • truth_value equals 0 and line_number_false is a non-existing line number, or truth_value is nonzero and line_number_true is a non-existing line number: Undefined line number.

INPUT (console)

INPUT [;] [prompt {;|,}] var_0 [, var_1] ...

Prints prompt to the screen and waits for the user to input values for the specified variables. The semicolon before the prompt, if present, stops a newline from being printed after the values have been entered. If the prompt is followed by a semicolon, it is printed with a trailing ?. If the prompt is followed by a comma, no question mark is added.

Parameters
  • prompt is a string literal.
  • var_0, var_1, ... are variable names or fully indexed array elements.
Notes
  • Values entered must be separated by commas. Leading and trailing whitespace is discarded.
  • String values can be entered with or without double quotes (").
  • If a string with a comma, leading or trailing whitespace is needed, quotes are the only way to enter it.
  • Between a closing quote and the comma at the end of the entry, only white- space is allowed.
  • If quotes are needed in the string itself, the first character must be neither a quote nor whitespace. It is not possible to enter a string that starts with a quote through INPUT.
  • If a given var_n is a numeric variable, the value entered must be number literal.
  • Characters beyond the 255th character of the screen line are discarded.
  • If user input is interrupted by Ctrl+Break, CONT will re-execute the INPUT statement.
Errors
  • If the value entered for a numeric variable is not a valid numeric literal, or the number of values entered does not match the number of variables in the statement, ?Redo from start is printed and all values must be entered again.
  • A Syntax error that is caused after the prompt is printed is only raised after the value shave been entered. No values are stored.

INPUT (files)

INPUT # file_num, var_0 [, var_1] ...

Reads string or numeric variables from a text file or the FIELD buffer of a random access file.

Parameters
  • file_num is the number of a file open in INPUT mode or a random-access file open in RANDOM mode.
  • var_0, var_1, ... are variable names or fully indexed array elements.
Notes
  • The # is mandatory. There may or may not be whitespace between INPUT and #.
  • String values can be entered with or without double quotes (").
  • Numeric values are terminated by  , LF, CR, ,.
  • Unquoted strings are terminated by LF, CR, ,.
  • Quoted strings are terminated by the closing quote.
  • Any entry is terminated by EOF character or its 255th character.
  • Leading and trailing whitespace is discarded.
  • If the entry cannot be converted to the requested type, a zero value is returned.
  • If file_num is open to KYBD:, INPUT# reads from the keyboard until a return or comma is encountered (as in a file). Arrow keys and delete are passed as their control characters (not scancodes!) preceded by CHR$(&hFF).
Errors
  • Input is requested after the end of a text file has been reached or an EOF character has been encountered: Input past end.
  • The last character of the field buffer is read: Field overflow.
  • file_num has a string value: Type mismatch.
  • file_num is greater than 32767: Overflow.
  • file_num is less than zero: Illegal function call.
  • file_num is not an open file: Bad file number.
  • file_num is not open for INPUT or RANDOM: Bad file mode.
  • file_num is open to a COM port and this is the first INPUT, LINE INPUT or INPUT$ call on that port since the buffer has filled up completely (i.e. LOF(file_num) has become zero): Communication buffer overflow.

IOCTL

IOCTL [#] file_num, control_string

Raises Illegal function call.

Notes
  • In GW-BASIC, IOCTL sends a control string to a device.
  • This statement is not implemented in PC-BASIC.
Errors
  • file_num has a string value: Type mismatch.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not an open file: Bad file number.
  • Otherwise: Illegal function call

KEY (macro list)

KEY {ON|OFF|LIST}

Turns the list of function-key macros on the bottom of the screen ON or OFF. If LIST is specified, prints a list of the 10 (or 12 with syntax=tandy) function keys with the function-key macros defined for those keys to the console.

Most characters are represented by their symbol equivalent in the current codepage. However, some characters get a different representation, which is a symbolic representation of their effect as control characters on the screen.

Code point Replacement Usual glyph
&h07 &h0E
&h08 &hFE
&h09 &h1A
&h0A &h1B
&h0B &h7F
&h0C &h16
&h0D &h1B
&h1C &h10
&h1D &h11
&h1E &h18
&h1F &h19

KEY (macro definition)

KEY key_id, string_value

Defines the string macro for function key key_id. Only the first 15 characters of string_value are stored.

Parameters
  • key_id is a numeric expression in the range [1—10] (or [1—12] when syntax=tandy).
  • string_value is a string expression.
Notes
  • If key_id is not in the prescribed range, the statement is interpreted as an event-trapping KEY statement.
  • If string_value is the empty string or the first character of string_value is CHR$(0), the function key macro is switched off and subsequent catching of the associated function key with INKEY$ is enabled.
Errors
  • key_id is not in [-32768—32767]: Overflow.
  • key_id is not in [1—255]: Illegal function call.
  • key_id has a string value: Type mismatch.

KEY (event switch)

KEY (key_id) {ON|OFF|STOP}

Controls event trapping of the key with identifier key_id. Event trapping is switched ON or OFF. STOP suspends event trapping until a KEY() ON is executed. Up to one event can be triggered during suspension, provided that event handling was switched on prior to suspension. The event triggered during suspension is handled immediately after the next KEY() ON statement. Event trapping can only be active during execution of a program, it does not work in direct mode.

Parameters

key_id is a numeric expression in [1—20]. Keys are:

1 F1
2 F2
3 F3
4 F4
5 F5
6 F6
7 F7
8 F8
9 F9
10 F10
11
12
13
14

Keys 15 to 20 are defined using the event trapping KEY definition statement.

Notes
  • With syntax=tandy, key 11 is F11 and key 12 is F12. Pre-defined keys 11—14 shift to 13—16.
Errors
  • key_id is not in [-32768—32767]: Overflow.
  • key_id is not in [0—20]: Illegal function call.
  • key_id has a string value: Type mismatch.

KEY (event definition)

KEY key_id, two_char_string

Defines the key to trap for key_id.

Parameters
  • key_id is a numeric expression in [15—20] (or [17—20] when syntax=tandy).
  • two_char_string is a string expression of length 2. The first character is interpreted as a modifier while the second character is interpreted as a scancode. The modifier character is a bitwise OR combination of the following flags:
    CHR$(&h80) Extended (ignored)
    CHR$(&h40) Caps Lock
    CHR$(&h20) Num Lock
    CHR$(&h10) not used
    CHR$(&h08) Alt
    CHR$(&h04) Ctrl
    CHR$(&h02) Shift (either side)
    CHR$(&h01) Shift (either side)
    For the unmodified key, the modifier character is CHR$(0).
Notes
  • If key_id is not in the prescribed range, no error is raised; such values are ignored. In GW-BASIC strange things can happen in this case: screen anomalies and crashes suggestive of unintended memory access.
  • If key_id is in [1—10] (or [1—12] when syntax=tandy), the statement is interpreted as a function-key macro definition.
  • The extended modifier &h80 refers to the additional keys that were introduced with the Model M 101-key keyboard in th earea between the main keyboard and the numerical keypad. These are the arrow keys, Home, End, PgUp, PgDn, Ins, Del as separate from the numerical keypad. PC-BASIC ignores this modifier; in a key definition, it does not make a difference whether or not it is set.
Errors
  • key_id is not in [-32768—32767]: Overflow.
  • key_id is not in [1—255]: Illegal function call.
  • key_id has a string value: Type mismatch.
  • two_char_string is longer than two: Illegal function call.
  • two_char_string has a numeric value: Type mismatch.

KILL

KILL filter_spec

Deletes one or more files on a disk device.

Parameters
  • The string expression filter_spec is a valid file specification indicating the files to delete. Wildcards are allowed. See FILES for a description of wildcards.
Notes
  • Be very careful with the use of wildcards in this statement: the DOS matching rules may not be the same as what is usual on your operating system, which could result in unexpected files being deleted.
  • This statement may not delete hidden file and files that do not have short names which are legal DOS names. However, this behaviour is not guaranteed so you must not depend on it.
Errors
  • filter_spec is a numeric value: Type mismatch.
  • A file with a base name equal to that of a file matching filter_spec is open: File already open
  • No file matches filter_spec : File not found
  • The user has no write permission: Permission denied
  • If a syntax error occurs after the closing quote, the file is removed anyway.

LCOPY

LCOPY [num]

Does nothing.

Parameters
  • num is a numeric expression in [0—255].
Notes
  • This statement does nothing in GW-BASIC. Presumably, it is left over from a statement in older versions of MS Basic that would copy the screen to the printer.
Errors
  • num is not in [-32768—32767]: Overflow.
  • num is not in [0—255]: Illegal function call.
  • num has a string value: Type mismatch.

LET

[LET] name = expression

Assigns the value of expression to the variable or array element name.

Parameters
  • name is a variable that may or may not already exist.
  • The type of expression matches that of name: that is, all numeric types can be assigned to each other but strings can only be assigned to strings.
Errors
  • name and expression are not of matching types: Type mismatch.

LINE

LINE [[STEP] (x0, y0)] - [STEP] (x1, y1) [, [attr] [, [B [F]] [, pattern]]]

Draws a line or a box in graphics mode. If B is not specified, a line is drawn from (x0, y0) to (x1, y1), endpoints inclusive. If B is specified, a rectangle is drawn with sides parallel to the screen and two opposing corners specified by (x0, y0) and (x1, y1). If the starting point is not given, the current graphics position is used as a staring point. If STEP is specified, (x0, y0) is an offset from the current position and (x1, y1) is an offset from (x0, y0). LINE moves the current graphics position to the last given endpoint. If F is specified with B, the rectangle is filled with the specified attribute. F and B may be separated by zero or more spaces.

Parameters
  • attr is a numeric expression in [0—255], which specifies the colour attribute of the line. If it is not given, the current attribute is used.
  • pattern is a numeric expression in [-32768—32767]. This is interpreted as a 16-bit binary pattern mask applied to consecutive pixels in the line: a 1 bit indicates a pixel plotted; a 0 bit indicates a pixel left untouched. The pattern starts at the most significant bit, which is applied to the topmost endpoint. If a box is drawn, the pattern is applied in the following counter-intuitive sequence: (x1, y1)—(x0, y1), (x1, y0)—(x0, y0), then (x1, y0)—(x1, y1), (x0, y0)—(x0, y1) if y0<y1 and y0, y1 reversed if y1<y0. When drawing a filled box, LINE ignores the pattern.
Notes
  • If a coordinate is outside the screen boundary, it is replaced with -1 (if less than 0) or the screen dimension (if larger than the screen dimension).
Errors
  • The statement ends in a comma and it is the first or third: Missing operand. If it is the second: Syntax error.
  • Any of the coordinates is not in [-32768—32767]: Overflow.
  • Any of the parameters has a string value: Type mismatch.

LINE INPUT (console)

LINE INPUT [;] [prompt_literal {;|,}] string_name

Displays the prompt given in prompt_literal and reads user input from the keyboard, storing it into the variable string_name. All input is read until Enter is pressed; the first 255 characters are stored. If the ; is given right after LINE INPUT, the Enter ending user input is not echoed to the screen.

Parameters
  • prompt_literal is a string literal. It makes no difference whether it is followed by a comma or a semicolon.
  • string_name is a string variable or array element.
Notes
  • If user input is interrupted by Ctrl+Break, CONT will re-execute the LINE INPUT statement.
  • Unlike INPUT, LINE INPUT does not end the prompt with ?.

LINE INPUT (files)

LINE INPUT # file_num, string_name

Reads string or numeric variables from a text file or the FIELD buffer of a random access file. All input is read until Enter is pressed; the first 255 characters are stored. file_num must be the number of a file open in INPUT mode or a random-access file open in RANDOM mode.

Parameters
  • string_name is a string variable or array element.
Notes
  • The # is mandatory. There may or may not be whitespace between INPUT and #.
  • Input is only terminated by a CR.
  • If file_num is open to KYBD:, LINE INPUT# reads from the keyboard until a return or comma is encountered (as in a file). Arrow keys and delete are passed as their control characters (not scancodes!) preceded by CHR$(&hFF).
Errors
  • Input is requested after the end of a text file has been reached or an EOF char has been encountered: Input past end.
  • The last character of the field buffer is read: Field overflow.
  • file_num is not an open file: Bad file number.
  • file_num is less than zero: Illegal function call.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not open for INPUT or RANDOM: Bad file mode.
  • file_num has a string value: Type mismatch.
  • file_num is open to a COM port and this is the first INPUT, LINE INPUT or INPUT$ call on that port since the buffer has filled up completely (i.e. LOF(file_num) has become zero): Communication buffer overflow.

LIST

LIST [line_number_0|.] [-[line_number_1|.]] [, file_spec [anything]]

Prints the program to the screen or a file, starting with line_number_0 up to and including line_number_1. Also stops program execution and returns control to the user. If the LIST statement ends with a file specification, anything further is ignored. In all cases, any further statements in a compound after LIST will be ignored, both in a program and in direct mode.

When listing to the screen, the same control characters are recognised as in the PRINT statement.

Notes
  • In GW-BASIC 3.23, LIST will not show line numbers 6553165535 inclusive. By default, PC-BASIC's LIST does show these lines. However, showing them can be disabled with the option hide-listing=65530.
Parameters
  • line_number_0 and line_number_1 are line numbers in the range [0—65529] or a . to indicate the last line edited. The line numbers do not need to exist; they specify a range. If the range is empty, nothing is printed.
  • The string expression file_spec is a valid file specification indicating the file to list to. If this file already exists, it will be overwritten.
Errors
  • A line number is greater than 65529: Syntax error.
  • file_spec has a numeric value: Type mismatch.
  • file_spec ends in a colon but is not a device name or drive letter: Bad file number.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).

LLIST

LLIST [line_number_0|.] [-[line_number_1|.]]

Prints the program to the line printer LPT1:, starting with line_number_0 up to and including line_number_1. Also stops program execution and returns control to the user. Any further statements on a line after LLIST will be ignored, both in a program and in direct mode.

Notes
  • In GW-BASIC 3.23, LLIST will not show line numbers 6553165535 inclusive. By default, PC-BASIC's LLIST does show these lines. However, showing them can be disabled with the option hide-listing=65530.
Parameters
  • line_number_0 and line_number_1 are line numbers in the range [0—65529]. or a . to indicate the last line edited. The line numbers do not need to exist; they specify a range. If the range is empty, nothing is printed.
Errors
  • A line number is greater than 65529: Syntax error.

LOAD

LOAD file_spec [, R]

Loads the program stored in a file into memory. Existing variables will be cleared and any program in memory will be erased. LOAD implies a CLEAR.

If ,R is specified, keeps all data files open and runs the specified file.

Parameters
  • The string expression file_spec is a valid file specification indicating the file to read the program from.
Errors
  • file_spec has a numeric value: Type mismatch.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).
  • The file specified in file_spec cannot be found: File not found.
  • A loaded text file contains lines without line numbers: Direct statement in file.
  • A loaded text file contains lines longer than 255 characters: Line buffer overflow. Attempting to load a text file that has LF rather than CR LF line endings may cause this error.

LOCATE

LOCATE [row] [, [col] [, [cursor_visible] [, [start_line] [, [stop_line] [,]]]]]

Positions the cursor at row, col on the screen and changes the cursor shape and visibility. cursor_visible may be 0 or 1. If cursor_visible is 0, it makes the cursor invisible; if it is 1, makes the cursor visible. This works only while a program is running. The cursor shape is adjusted within a character cell to start from start_line and end on end_line where start_line and end_line are in [0—31]. If start_line or end_line is greater than the character cell height (15), substitute 15.

Notes
  • On emulated VGA cards, the cursor shape parameters are interpreted in a complicated way that is intended to maintain functional compatibility with CGA.
  • In GW-BASIC, cursor shape is preserved after pressing Ins twice. The insert-mode cursor is different from the usual half-block. In PC-BASIC, insert mode resets the cursor shape to default.
  • Cursor shape and visibility options have no effect in graphics mode.
  • Locate accepts a 5th comma at the end, which is ignored.
Errors
  • Any parameter has a string value: Type mismatch.
  • Any parameter is not in [-32768—32767]: Overflow.
  • row is outside the current view area: Illegal function call.
  • col is greater than the current width: Illegal function call.
  • cursor_visible is not in [0, 1] ([0—255] on Tandy/PCjr): Illegal function call.

LOCK

LOCK [#] file_number [, record_0] LOCK [#] file_number, [record_0] TO record_1

Locks a file or part of a file against access by other users. On a RANDOM file, record_0 is the first record locked and record_1 is the last record locked. On any other kind of file record_0 and record_1 have no effect. If record_0 is not specified, it is assumed to be 1. If no records are specified, the whole file is locked.

Parameters
  • file_number is a numeric expression in [0—255].
  • record_0 and record_1 are numeric expressions in [1—2^25-2].
Notes
  • In GW-BASIC under MS-DOS, the LOCK command requires SHARE.EXE to be loaded. The maximum number of locks is specified in the MS-DOS SHARE command. If SHARE has not been activated or all locks are used, LOCK raises Permission denied. PC-BASIC behaves as if SHARE has been activated with unlimited locks.
  • If file_number is open for RANDOM, LOCK and UNLOCK statements must match in terms of record_0 and record_1. An non-matching UNLOCK will raise Permission denied.
  • To check if another open file is the same file, PC-BASIC only looks at the base name of the file, i.e. its DOS name without directories. As a consequence, if a file "test.txt" is open and locked, an attempt to lock a file "dir\test.txt" will fail, even if these are different files. Conversely, if two file names are different but point to the same file in the file system (for example due to file system links), then these will be considered as different files by BASIC.
Errors
  • Any parameter has a string value: Type mismatch.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not in [0—255]: Illegal function call.
  • file_num is not an open file: Bad file number.
  • LOCK (part of) a file with the same name as a file already locked: Permission denied.
  • record_0 or record_1 is not in [1—2^25-2]: Bad record number.

LPRINT

See PRINT.


LSET

LSET string_name = expression

Copies a string value into an existing string variable or array element. The value will be left-justified and any remaining characters are replaced by spaces.

Parameters
  • string_name is a string variable or array element.
  • expression is a string expression.
Notes
  • If expression has a value that is longer than the length of the target variable, it is truncated at the tail to the length of the target variable.
  • If string_name has not been allocated before, this statement has no effect.
  • Use LSET, RSET or MID$ to copy values into a FIELD buffer.
  • If LET is used on a FIELD variable instead of L|RSET, the variable is detached from the field and a new, normal string variable is allocated.
Errors
  • string_name is not a string variable: Type mismatch.
  • expression does not have a string value: Type mismatch.

MERGE

MERGE file_spec

Overlays the lines of a program from a plain-text program file into the existing program. The loaded lines overwrite existing lines if they have the same line number.

Parameters
  • The string expression file_spec is a valid file specification indicating the file to read the program from.
Errors
  • file_spec cannot be found: File not found.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).
  • file_spec was not saved as plain text: Bad file mode.
  • A loaded text file contains lines without line numbers: Direct statement in file.
  • A loaded text file contains lines longer than 255 characters: Line buffer overflow. Attempting to load a text file that has LF rather than CR LF line endings may cause this error.

MID$ (statement)

MID$(string_name, position [, length]) = substring

Replaces part of string_name with substring.

Parameters
  • string_name is a valid string variable name.
  • position is a numeric expression between 1 and the string length, inclusive.
  • length is a numeric expression in [0—255].
Notes
  • No whitespace is allowed between MID$ and (.
  • If substring is longer than length, only the first length characters are used.
  • If substring is shorter than length, only LEN(substring) characters are replaced.
Errors
  • position is greater than the length of string_name: Illegal function call, except if length is specified as 0.
  • position is not in [1—255]: Illegal function call.
  • length is not in [0—255]: Illegal function call.
  • position or length are not in [-32768—32767]: Overflow.

MKDIR

MKDIR dir_spec

Creates a new directory on a disk device.

Parameters
  • The string expression dir_spec is a valid file specification that specifies the path of the new directory on a disk device.
Errors
  • dir_spec is not a string: Type mismatch.
  • The parent directory does not exist: Path not found.
  • The directory name already exists on that path: Path/File access error.
  • The user has no write permission: Permission denied.

MOTOR

MOTOR [num]

Does nothing.

Parameters
  • num is a numeric expression in [0—255].
Notes
  • In GW-BASIC, this statement turns on the cassette motor if num is nonzero or omitted, and turns it off if num is zero. This is not implemented in PC-BASIC.
Errors
  • num has a string value: Type mismatch.
  • num is not in [-32768—32767]: Overflow.
  • num is not in [0—255]: Illegal function call.

NAME

NAME old_name AS new_name

Renames the disk file old_name into new_name.

Parameters
  • The string expressions old_name and new_name are valid file specifications giving the path on a disk device to the old and new filenames, respectively.
Notes
Errors
  • old_name or new_name have number values: Type mismatch.
  • old_name does not exist: File not found.
  • A file with a base name equal to that of old_name or new_name is open: File already open.
  • new_name exists: File already exists.

NEW

NEW

Stops execution of a program, deletes the program in memory, executes CLEAR and RESTORE and returns control to the user.


NEXT

NEXT [var_0 [, var_1] ...]

Iterates a FOR—NEXT loop: increments the loop variable and jumps to the FOR statement. If no variables are specified, next matches the most recent FOR statement. Several nested NEXT statements can be consolidated into one by using the variable list. If one or more variables are specified, their order must match the order of earlier FOR statements.

Parameters
  • var_0, var_1, ... are numeric variables which are loop counters in a FOR statement.
Errors
  • No FOR statement is found to match the NEXT statement and variables: NEXT without FOR.
  • var_0, var_1, ... are string variables: NEXT without FOR.
  • The (implicit or explicit) loop variable is an integer variable and is taken outside the range [-32768, 32767] when incremented after the final iteration: Overflow .

NOISE

NOISE source, volume, duration

Generates various kinds of noise.

Parameters
  • source is a numeric expression in [0—7]. It indicates the type of noise:
    source type top of frequency band (Hz)
    0 periodic 6991
    1 periodic 3495
    2 periodic 1747
    3 periodic last tone played on voice 2
    0 white noise 6991
    1 white noise 3495
    2 white noise 1747
    3 white noise last tone played on voice 2
  • volume is a numeric expression in [0—15].
  • duration is a numeric expression.

Volume and duration are determined in the same way as for the SOUND statement; see there.

Notes
  • This statement is only available if syntax={pcjr|tandy} is set.
Errors
  • SOUND ON has not been executed: Illegal function call.
  • duration is not in [-65535—65535]: Illegal function call.
  • volume is not in [0—15]: Illegal function call.
  • source is not in [0—7]: Illegal function call.

ON (calculated jump)

ON n {GOTO|GOSUB} line_number_0 [, line_number_1] ...

Jumps to the nth line number specified in the list. If n is 0 or greater than the number of line numbers in the list, no jump is performed. If GOTO is specified, the jump is unconditional; if GOSUB is specified, jumps to a subroutine.

Parameters
  • n is a numeric expression in [0—255]. The expression must not start with the STRIG, PEN, PLAY or TIMER function keywords; if you need these functions, the expression must be bracketed.
  • line_number_0, line_number_1, ... are existing line numbers in the program.
Errors
  • n has a string value: Type mismatch.
  • n is not in [-32768—32767], Overflow .
  • n is not in [0—255]: Illegal function call.
  • The line number jumped to does not exist: Undefined line number.

ON (event trapping)

ON {COM(n)|KEY(n)|STRIG(n)|PEN|PLAY(n)|TIMER(x)} GOSUB line_number

Defines an event trapping subroutine. The type of event is given by one of the following keywords:

COM(n) The event is triggered if data is present in the input buffer of the COMn:. n is the port number in [1,2].
KEY(n) The event is triggered if key n is pressed. n is the key number [1—20] defined in the KEY statement.
STRIG(n) They event is triggered if fire button n is pressed. n in [0,2,4,6] refer to the two fire triggers on two joysticks.
PEN The event is triggered if the light pen is on the screen. (In PC-BASIC, the light pen is emulated by default by the right mouse button).
PLAY(n) The event is triggered if there are exactly n notes left on the music background queue. n is a numeric expression in [1—32].
TIMER(x) The event is triggered every x seconds after the TIMER ON statement. x is a numeric expression in [1—86400].
Notes
Errors
  • n or x has a string value: Type mismatch.
  • n is not in [-32768—32767]: Overflow.
  • n or x is outside the specified range: Illegal function call.

ON ERROR

ON ERROR GOTO {line_number|0}

Turns error trapping on or off. When line_number is set, any error causes the error handling routine starting at that line number to be called; no message is printed and program execution is not stopped. The error handling routine is ended by a RESUME statement. While in an error handling routine, events are paused and error trapping is disabled. After the RESUME statement, any triggered events are picked up in the following order: KEY, TIMER, PLAY - the order of the others is unknown. Unlike event trapping, error trapping remains active when no program is running. ON ERROR GOTO 0 turns off error trapping.

Parameters
  • line_number is an existing line number in the program.
Notes
  • It is not possible to start the error handler at line number 0.
Errors
  • line_number does not exist: Undefined line number.

OPEN

OPEN mode_char, [#] file_num, file_spec [, rec_len] OPEN file_spec [FOR {INPUT|OUTPUT|APPEND|RANDOM}] [ACCESS {READ|WRITE|READ WRITE}] [SHARED|LOCK {READ|WRITE|READ WRITE}] AS [#] file_num [LEN = rec_len]

Opens a data file on a device.

Parameters
  • The string expression file_spec is a valid file specification.
  • file_num is a numeric expression in [1—max_files], where max_files is the maximum file number (default 3).
  • rec_len is a numeric expression in [1—128]: the record length.
  • mode_char is a string expression of which the first character is one of ["I", "O", "A", "R"].
Access modes

The FOR modes or mode_char are as follows:

mode_char FOR Effect
"I" INPUT Opens a text file for reading and positions the file pointer at the start.
"O" OUTPUT Truncates a text file at the start and opens it for writing. Any data previously present in the file will be deleted.
"A" APPEND Opens a text file for writing at the end of any existing data.
"R" RANDOM Opens a file for random access; the file is divided in records of length rec_len. If LEN is not specified, the record length defaults to 128. The file contents can be accessed using GET and PUT of the FIELD buffer; the FIELD buffer can be accessed through FIELD variables or through PRINT# and INPUT# statements.

If no FOR mode or mode_char is specified, the file is opened for RANDOM.

If both FOR and ACCESS are specified, any ACCESS mode is allowed for RANDOM but for the other modes the access must match as follows:

FOR default ACCESS allowed ACCESS
INPUT READ READ
OUTPUT WRITE WRITE
APPEND READ WRITE READ WRITE
RANDOM READ WRITE all
Sharing and locks

If neither SHARED nor LOCK are specified. Inside this process, a file may be opened multiple times for INPUT or RANDOM but only once for OUTPUT or APPEND, as long as it is again opened in default mode. It may not be opened in SHARED or any LOCK modes.

If SHARED, LOCK READ, LOCK WRITE or LOCK READ WRITE is specified, whether two OPEN statements may access the same file depends on one's LOCK status and the other's ACCESS status and vice versa. For two OPEN statements as follows: OPEN "file" lock_1 AS 1
OPEN "file" ACCESS acc_2 SHARED AS 2
the following combinations are allowed:

Access allowed acc_2
READ WRITE READ WRITE
lock_1 SHARED yes yes yes
LOCK READ no yes no
LOCK WRITE yes no no
LOCK READ WRITE no no no

In GW-BASIC under MS-DOS with SHARE.EXE active, these locks should be enforced across a network as well as inside a single BASIC process. Without SHARED and LOCK, the file is locked exclusively for use by the GW-BASIC process. By contrast, in PC-BASIC, the locks are only implemented internally. Whether other processes may access the file will depend on the host OS.

To check if another open file is the same file, PC-BASIC only looks at the base name of the file, i.e. its DOS name without directories. As a consequence, if a file "test.txt" is open and locked, an attempt to lock a file "dir\test.txt" will fail, even if these are different files. Conversely, if two file names are different but point to the same file in the file system (for example due to file system links), then these will be considered as different files by BASIC.

File specifications

A file specification file_spec is a non-empty string expression of the form "[device:]parameters", where device is a PC-BASIC device and the form of the parameters is specific to the type of device. If device is omitted, the current device (one of the disk devices or CAS1:) is used.

Disk devices A:Z: and @:

parameters must specify a valid file path of the form [\][dirname\] ... filename.

PC-BASIC follows DOS file system conventions. Directory names are separated with backslashes \ (even if the host OS separates paths with forward slashes). File and directory names consist of a 8-character name and 3-character extension. Names are case insensitive. Permissible characters for both filename and extension are the printable ASCII characters in the range &h20&h7E excluding the characters " * + . , / : ; < = > ? \ [ ] |. Spaces are allowed but leading and trailing spaces are ignored. The names AUX, CON, PRN and NUL are reserved as device aliases and are not legal names for files or directories on a disk device.

A path starting with a backslash is interpreted as an absolute path, starting at the root of the specified disk device. Otherwise, the path is interpreted as relative to the current directory on the specified device. The special directory name .. refers to the parent directory of a preceding path, or the parent directory of the current directory if no path is given. The special directory name . refers to the same directory as given by the preceding path, or the current directory if no preceding path is given.

If the file name provided does not contain any dots, the LOAD, SAVE, BLOAD, BSAVE, CHAIN, MERGE, RUN, and LIST statements append the default extension .BAS. To refer to a file name without an extension, the file specification should end in a dot .. For other statements, appending a dot is allowed but not required.

Compatibility notes

Unlike PC-BASIC, some versions of MS-DOS allow certain characters in the range &h7F&hFF. However, their permissibility and interpretation depends on the console code page, which may be different from the display code page that affects GW-BASIC. Depending on its console code page, MS-DOS will replace accented letters by their unaccented uppercase variant. Some DOS implementations will remove spaces from filenames; notably, this is the case on DOSBox.

In order to allow access to files whose name on the host system does not conform to DOS standards while maintaining compatibility with GW-BASIC, PC-BASIC will follow these steps to match DOS-style file names to host file names:

  1. Look for a file with the name as provided. This can be a long file name which may contain non-permissible characters and which will be case sensitive if your file system is.
  2. If such a file is not found, it will truncate the name provided to all-uppercase 8.3 format and look for an exact match. The truncated name consists of the first 8 characters before the first dot, followed by the first three characters after the first dot. If the resulting file name contains non-permissible characters, an error will be raised.
  3. Look for 8.3 names in mixed case which match the name provided in a case-insensitive way. Such files are searched in lexicographic order. File names longer than 8.3 will not be matched, unless their name is entered exactly. On Windows, the name matched can be a short filename as well as a long filename provided it is of 8.3 length — it may, for example, contain spaces and thus not be a valid Windows short file name.

If the file name provided ends in a single dot and contains no other dots, PC-BASIC will first match the name as provided; if this is not found, it will match the name as provided but without the single dot. The 8.3 format of such a file name will match file names with and without the dot, in lexicographic order.

If no matching file is found for an output file name, a new file will be created with an all-uppercase 8.3 file name.

Cassette device CAS1:
parameters can be a file name of up to eight characters. Cassette file names are case sensitive, have no path or extension, may be empty and do not need to be unique. They may contain any character in the range &h20&hFF. On the cassette device, when called in direct mode, OPEN, CHAIN, MERGE, LOAD and BLOAD will print a message to the console for each file found while winding the tape. The message consists of the filename followed by a dot and the file type and concluded with a status message. The file type is one of the following:
A
Program file in text format
B
Program file in tokenised format
D
Data file
M
BSAVE memory image
P
Program file in protected format
If the file does not match the file specification and required file type, the status is Skipped; if the file matches, the status is Found. When called from a program, these statements do not print messages to the console. If the device was specified explicitly, parameters may also be empty. In this case the first file of the appropriate type is opened.
Console and parallel devices SCRN:, KYBD:, and LPTn:
These devices do not allow further device parameters.
Serial devices COMn:

When opening a COM port, the file_spec has the form "COMn:[speed[,parity[,data[,stop[,RS][,CS[n]][,DS[n]][,CD[n]][,LF][,PE]]]]]" The first four parameters after the device colon must be given in the order specified but the named parameters can be given in any order. The meaning of the parameters is:

Parameter Default Meaning
speed 300 Baud (bps) rate for the connection. speed is one of [75, 110, 150, 300, 600, 1200, 1800, 2400, 4800, 9600].
parity E Parity bit convention. parity is one of [S, M, O, E, N].
parity Meaning Effect
S SPACE Parity bit always set to 0.
M MARK Parity bit always set to 1.
O ODD Parity bit set so that character parity is odd.
E EVEN Parity bit set so that character parity is even.
N NONE No parity bit transmitted or received.
data 7 Data bits per byte. data must be one of [4, 5, 6, 7, 8]. A byte consists of the data bits plus parity bit, if any. Byte size must be in the range [5—8]: if data is 4, parity must not be N; if data is 8, parity must be N.
stop 1 The number of stop bits. stop must be 1 or 2. Default is 2 if speed is 75 or 110; 1 otherwise.
RS no Suppress Request To Send.
CS[n] CS1000 Set Clear To Send timeout to n milliseconds. If n is 0 or not given, disable CTS check. Default is CS0 if RS is set; CS1000 otherwise.
DS[n] DS1000 Set Data Set Ready timeout to n milliseconds. If n is 0 or not given, disable DSR check.
CD[n] CD0 Set Carrier Detect timeout to n milliseconds. If n is 0 or not given, disable CD check.
LF no Send a line feed after each carriage return.
PE no Enable parity checking (This setting is ignored by PC-BASIC).
Notes
  • If a COM port is opened for RANDOM, access is byte-for-byte rather than through FIELD records; PRINT# and INPUT# access the port directly. rec_len sets the number of bytes read by the GET and PUT statements.
  • For INPUT, OUTPUT and APPEND modes, LEN may be specified but is ignored.
  • If I/O is attempted contravening the FOR mode specified, the PRINT or INPUT statement will raise Bad file mode.
  • If RANDOM I/O is attempted contravening the ACCESS mode specified, the PUT or GET statement will raise Path/File access error.
  • The # is optional and has no effect.
Errors
  • file_spec is empty or a non-existent device: Bad file number.
  • FOR APPEND ACCESS WRITE is specified: Path/File access error.
  • FOR and ACCESS mismatch in other ways: Syntax error.
  • The COM: file_spec parameters do not follow the specification: Bad file name.
  • The CAS1: file_spec contains disallowed characters: Bad file number.
  • A file with the same name is already open for OUTPUT or APPEND: File already open. This is only raised for COMn:, CASn: and disk devices.
  • rec_len or file_num have string values: Type mismatch.
  • file_spec or mode_char have number values: Type mismatch.
  • file_num is not in [-32768—32767]: Overflow.
  • file_num is not in [0—255]: Illegal function call.
  • file_num is not in [1—max_files]: Bad file number.
  • rec_len is not in [-32768—32767]: Overflow.
  • rec_len is not in [1—128]: Illegal function call.
  • mode_char is empty or the first character is not in ["I", "O", "A", "R"]: Bad file mode.

OPTION BASE

OPTION BASE n

Sets the starting index of all arrays to n.

Parameters
  • n is a literal digit 0 or 1. Expressions are not allowed.
Notes
  • If OPTION BASE has not been called, the first array allocation defaults to starting index 0.
Errors
  • n is not a digit 0 or 1: Syntax error.
  • OPTION BASE 1 is called but an array has already been allocated before: Duplicate definition.
  • OPTION BASE is called more than once with different starting index: Duplicate definition.

OUT

OUT port, value

Sends a byte to an emulated machine port.

The following machine ports are emulated in PC-BASIC:

port Effect
&h201 resets the game port (joystick port)
&h3C5 sets the write bitmask for SCREEN 7, 8, 9 colour planes. bitmask = 2 ^ value.
&h3CF sets the read colour plane to value.
&h3D8 if value = &h1A, enable composite colorburst.
if value = &h1E, disable composite colorburst.
Requires video={cga, tandy, pcjr}.
Notes
  • Only a limited number of machine ports are emulated.
  • In GW-BASIC under MS-DOS, the sequence needed to set the colour plane mask is: OUT &h3C4, 2
    OUT &h3C5, 2 ^ plane
    The sequence needed to set the colour plane is: OUT &h3CE, 4
    OUT &h3CF, plane
    The initial OUT statements currently have no effect in PC-BASIC.
Parameters
  • port is a numeric expression in [-32768—65535].
  • value is a numeric expression in [0—255].
Errors
  • port or value has a string value: Type mismatch.
  • port is not in [-32768—65535]: Overflow.
  • value is not in [-32768—32767]: Overflow.
  • value is not in [0—255]: Illegal function call.

PAINT

PAINT [STEP] (x, y) [, attrib [, border [, background]]]

Flood-fills the screen with a colour or pattern, starting from the given seed point.

Parameters
  • x, y are numeric expressions in the range [-32768—32767] If STEP is specified, x y are offsets from the current position. If the seed point is outside the visible screen area, no flood fill is performed.
  • attrib is an expression that specifies the fill attribute or pattern. If not specified, the current foreground attribute is used.
  • If attrib has a number value, it must be in [0—255]; it specifies the colour attribute used to fill.
  • If attrib has a string value, it specifies a tile pattern (see below).
  • border is a numeric expression in [0—255]. It specifies the attribute of the fill boundary (see below).
  • background is a string expression that represents a background tile pattern to ignore when determining boundaries (see below).
Tile patterns

A tile pattern can be specified by a string of up to 255 characters. The interpretation of the string depends on the number of bits per pixel and on the current screen mode.

1 bit per pixel (e.g. SCREEN 2)
Here is an example:
76543210 Byte value
*....... &h80
.*...... &h40
..*..... &h20
...*.... &h10
....*... &h08
.....*.. &h04
......*. &h02
This diagonal stripe pattern can thus be produced with PAINT (0, 0), CHR$(128)+CHR$(64)+CHR$(32)+CHR$(16)+CHR$(8)+CHR$(4)+CHR$(2)
SCREEN 7, 8, 9
The tile pattern is always 8 pixels wide. The first character in the pattern string contains the first bit of each of these 8 pixels, the second character contains the second bits, etc. For example, in a 2-bits-per-pixel mode, four colour attributes can be used in the pattern. To create a diagonal stripe pattern of the same shape, in attribute &h03, we now need a tile string that is twice as long:
Attribute bit 76543210 Byte value
0 *....... &h80
1 *....... &h80
0 .*...... &h40
1 .*...... &h40
0 ..*..... &h20
1 ..*..... &h20
0 ...*.... &h10
1 ...*.... &h10
0 ....*... &h08
1 ....*... &h08
0 .....*.. &h04
1 .....*.. &h04
0 ......*. &h02
1 ......*. &h02
If the pattern string is truncated before all bits of the last line have been defined, the remaining bits will be zero.
SCREEN 1, 3, 4, 5 , 6
Each row of the tile pattern represents a screen row. Colours are encoded in consecutive bits; the more bits per pixel, the narrower the pattern is. For 2 bits per pixel, the pattern is 4 pixels wide; for 4 bits per pixel it is 2 pixels wide. The following pattern string encodes a diagonal dotted stripe in two colours:
3210 76543210 Byte value
2000 *....... &h80
1000 .*...... &h40
0200 ..*..... &h20
0100 ...*.... &h10
0020 ....*... &h08
0010 .....*.. &h04
0002 ......*. &h02

The tile pattern is anchored to the screen; imagine a grid starting at (0,0) and covering the screen. Whenever an area is tile-filled, the tiles are put into this grid. In this way, adjacent areas will have continuous tiling even if they were filled from different seed points.

Boundaries

A solid flood fill stops at pixels that have the same attribute as the fill or that have the specified border attribute, if specified. A tiling flood fill stops at the specified border attribute; if no border attribute is specified, it stops at the current foreground attribute. A tiling flood fill also stops at scan line intervals that are the same as the tiling pattern for that line, unless a background pattern is specified and the interval also equals the background pattern for that line.

The background tile pattern is constructed just like the tile pattern. However, only the first row of the background tile is taken into account; the rest is ignored. The background tile must not match the attribute tile, or more than two consecutive rows of it.

Errors
  • If more than two consecutive rows of the attribute tile (or all rows, if there are less than three) equal the first row of the background tile: Illegal function call.
  • background has a number value: Illegal function call.
  • border,x, or y have a string value: Type mismatch.
  • border,x, or y are not in [-32768—32767]: Overflow.
  • border is not in [0—255]: Illegal function call.
  • attrib is numeric and not in [-32768—32767]: Overflow.
  • attrib is numeric and not in [0—255]: Illegal function call.

PALETTE

PALETTE [attrib, colour]

Assigns a colour to an attribute. All pixels with that attribute will change colour immediately. If no parameters are specified, PALETTE resets to the initial setting.

Parameters
  • attrib is a numeric expression between 0 and the current palette size, less one.
  • colour is a numeric expression between -1 and the maximum number of colours for the current screen mode, less one. If colour equals -1, the palette remains unchanged.
Errors
  • attrib or colour has a string value: Type mismatch.
  • attrib or colour is not in [-32768—32767]: Overflow
  • attrib or colour is not in range: Illegal function call

PALETTE USING

PALETTE USING int_array_name {(|[} start_index {)|]}

Assigns new colours to all attributes.

Parameters
  • int_array_name is a single- or multidimensional array of integers (%) that will supply the new values for the palette.
  • start_index is a numeric expression that indicates at which index in the array to start mapping to the palette.
Notes
  • Array values are assigned to palette entries in the order in which they are stored in memory. See Arrays for details about the layout of arrays in memory.
  • If an array entry has value -1, the matching attribute is left unchanged.
Errors
  • int_array_name has not been allocated: Illegal function call. The array will not be automatically allocated.
  • int_array_name is not an integer array: Type mismatch.
  • int_array_name is too short: Illegal function call.
  • start_index has a string value: Type mismatch.
  • start_index is not in [-32768—32767]: Overflow
  • start_index is outside array dimensions: Subscript out of range

PCOPY

PCOPY src, dst

Copies the screen page src to dst. All text and graphics on dst is replaced by those of src.

Parameters
  • src and dst are numeric expressions between 0 and the current video mode's number of pages, less one.
Errors
  • src or dst has a string value: Type mismatch.
  • src or dst is not in [-32768—32767]: Overflow.
  • src or dst is out of range: Illegal function call.

PEN (statement)

PEN {ON|OFF|STOP}

Controls event trapping and read access of the light pen (emulated through the mouse in PC-BASIC). PEN ON switches pen reading and trapping on. PEN OFF switches it off. PEN STOP suspends PEN event trapping until PEN ON is executed. Up to one event can be triggered during suspension, provided that event handling was switched on prior to suspension. The event triggered during suspension is handled immediately after the next PEN ON statement.


PLAY (event switch)

PLAY {ON|OFF|STOP}
  • ON: enables ON PLAY event trapping of the music queue.
  • OFF: disables trapping.
  • STOP: halts trapping until PLAY ON is used. Events that occur while trapping is halted will trigger immediately when trapping is re-enabled.

PLAY (music statement)

PLAY [mml_string_0] [, [mml_string_1] [, mml_string_2]]

Plays the tune defined by the Music Macro Language strings mml_string_0, ....

Unless syntax={tandy | pcjr} is set, only the single-voice syntax is available. The three separate MML strings correspond to the three voices of the PCjr/Tandy sound adapter. The notes in these strings are played synchronously.

Parameters
  • mml_string_0, mml_string_1, mml_string_2 are string expressions in MML.
  • At least one parameter must be provided and the statement must not end in a comma.
Music Macro Language reference
Notes and Pauses
Command Effect
{A|B|C|D|E|F|G}[#|+|-][m] Play a note.
+ or # indicates sharp.
- indicates flat.
m is a numeric literal and indicates duration of an mth note. m is in the range [0—64]. If m=0 or omitted, use the default length.
Nn Play note n, in the range [0—84] (7 octaves).
n = 0 means rest.
On Set the current octave to n, in the range [0—6]. Default is 4.
> Increase the current octave by 1, with a maximum of 6.
< Decrease the current octave by 1, with a minimum of 0.
Pn Pause for the duration of an nth note. n is in the range [0—64]. If n=0, this has no effect.
Timing commands
Command Effect
. Increase the duration of the preceding note by 1/2 times its normal duration. Periods can be repeated to increase duration further.
Ln Set the duration of following note to an nth note. (n=4 is a quarter note, etc.) n is in the range [1—64].
MN Normal: 7/8 of the duration is sound, with 1/8 silence. Default mode.
ML Legato: full duration is sound.
MS Staccato: 3/4 of the duration is sound, with 1/4 silence.
Tn Sets the tempo to n L4s per minute. n is in the range [32—255]. Default is 120.
Background-mode commands

These commands affect SOUND, PLAY and BEEP

Command Effect
MB Turns on background mode; sound commands exit without waiting for the music to finish. The music keeps playing while other commands are executed. There can be up to 32 notes in the background music queue; if more notes are played, PLAY will block until there are only 32 left. Note that the gaps between notes in the default articulation and in staccato are counted as separate notes on the queue.
MF Turns off background mode; sound commands block. Default mode.
Subroutine command
Command Effect
Xs Execute substring. s is one of the following:
  • a string variable name followed by a;
  • the result of VARPTR$() on a string variable
Volume control

Volume control is available on syntax={tandy | pcjr} only:

Command Effect
Vn Set the volume to n, in the range [-1—15]. -1 means full volume. If SOUND ON has not been executed, this has no effect.
MML Parameters

Numeric variables n in the commands above can be:

  • an integer literal, e.g. PLAY "L4G"
  • a numeric variable name or array element var preceded by = and followed by ;. For example, PLAY "L=VAR;G" or PLAY "L=A(1);G"
  • the result of VARPTR$(var) preceded by =. For example, PLAY "L=" + VARPTR$(VAR) + "G"

Note that only number literals may follow named notes and dereferencing variables or arrays is not allowed there. It is an error to write PLAY "G=VAR;" or PLAY "G=" + VARPTR$(VAR). Use PLAY "G4" or PLAY "L=VAR;G" or PLAY "L=" + VARPTR$(VAR) + "G" instead.

Errors
  • mml_string has a numeric value: Type mismatch.
  • mml_string has errors in the MML: Illegal function call.
  • A variable in an MML string is of incorrect type: Type mismatch.
  • No MML string is specified: Missing operand.
  • If SOUND ON has not been executed, using the three-voice syntax will raise Syntax error.

POKE

POKE address, value

Sets the value of the memory byte at segment * 16 + address to value, where segment is the current segment set with DEF SEG.

Parameters
  • address is a numeric expression in [-32768—65535]. Negative values are interpreted as their two's complement.
  • value is a numeric expression in [0—255].
Notes
  • The memory is only partly emulated in PC-BASIC. See Memory model for supported addresses. Outside emulated areas of memory, this statement has no effect.
Errors
  • address or value has a string value: Type mismatch.
  • address is not in [-32768—65535]: Overflow.
  • value is not in [-32768—32767]: Overflow.
  • value is not in [0—255]: Illegal function call.

PSET and PRESET

{ PSET | PRESET } [STEP] (x, y) [, attrib]

Change the attribute of a pixel on the screen at position (x, y). If STEP is specified, (x, y) is an offset from the current position.

If attrib is between 0 and the screen mode's palette size, the pixel is changed to attribute attrib. If attrib is larger than the palette size, the pixel's attribute is changed to the highest legal attribute value. If attrib is not specified, PSET changes the attribute to the current foreground attribute while PRESET changes it to zero.

Parameters
  • x, y are numeric expressions in [-32768—32767].
  • attrib is a numeric expression in [0—255].
Errors
  • x or y has a string value: Type mismatch.
  • attrib, x or y or the physical coordinates they translate into are not in [-32768—32767]: Overflow.
  • attrib is not in [0—255]: Illegal function call.

PRINT and LPRINT

{LPRINT|{PRINT|?} [# file_num,]} [expr_0|;|,|SPC(n)|TAB(n)] ... [USING format; uexpr_0 [{;|,} uexpr_1] ... [;|,]]

Writes expressions to the screen, printer, or file. If LPRINT is used, output goes to LPT1:. If file_num is specified, output goes to the file open under that number. ? is a shorthand for PRINT.

When writing a string expression to the screen, the following control characters have special meaning. Other characters are shown as their corresponding glyph in the current codepage.

Code point Control character Effect
&h07 BEL Beep the speaker.
&h08 BS Erase the character in the previous column and move the cursor back.
&h09 HT Jump to the next 8-cell tab stop.
&h0A LF Go to the leftmost column in the next row; connect the rows to one logical line.
&h0B VT Move the cursor to the top left of the screen.
&h0C FF Clear the screen.
&h0D CR Go to the leftmost column in the next row.
&h1C FS Move the cursor one column to the right.
&h1D GS Move the cursor one column to the left.
&h1E RS Move the cursor one row up.
&h1F US Move the cursor one row down.

Expressions can optionally be separated by one or more of the following keywords:

Keyword Effect
; Attaches two expressions tight together; strings will be printed without any space in between, numbers will have one space separating them, in addition to the space or minus sign that indicate the sign of the number.
, The expression after will be positioned at the next available zone. The output file is divided in 14-character zones; if the width of the file is not a multiple of 14, the remaining spaces are unused and the first zone of the next line is used instead. If the file has a width of less than 14 characters, the zones are determined as if the file were wrapping continuously.
SPC(n) Produces n spaces, where n is a numeric expression. if n is less than zero, it defaults to zero. If n is greater than the file width, it is taken modulo the file width.
TAB(n) Moves to column n, where n is a numeric expression. if n is less than zero, it defaults to zero. If n is greater than the file width, it is taken modulo the file width. If the current column is greater than n, TAB moves to column n on the next line.

If the print statement does not end in one of these four separation tokens, a newline is printed after the last expression. String expressions can be separated by one or more spaces, which has the same effect as separating by semicolons.

Format string syntax

A USING declaration occurs at the end of an [L]PRINT[#] statement and writes a formatted string to the screen, printer or file. The following tables list the format tokens that can be used inside the format string.

_ Escape character; causes the next character in the format string to be printed as is rather than interpreted as a format token.

For string expressions:

! Prints the first character of a string.
\\ Prints 2 or more characters of a string. A greater number of characters is selected by separating the \s by spaces.
& Prints the whole string.

For numeric expressions, the format string specifies a width and alignment.

# Indicate a position for a digit.
. Indicate the decimal point.
, Before the decimal point: cause digits to be grouped in threes separated by commas. After the decimal point it is not a token. Provides one digit position.

The number of characters in the field must not exceed 24.

Tokens preceding the number field:

+ Cause the sign to be printed for positive as well as negative numbers. The sign is to be printed to the left of the number.
** Cause any leading spaces to be replaced with *s. Provides two digit positions.
$$ Cause a $ to be printed to the left of the number. Provides one digit position.

Tokens trailing the number field:

+ Cause the sign to be printed for positive as well as negative numbers. The sign will be printed to the right of the number.
- Cause the sign for negative numbers to be printed to the right of the number. Note that - preceding the field is not a token but printed literally.
^^^^ Specify that scientific notation E+00 is to be used.

Numeric expressions are always fully printed, even if they do not fit in the positions specified. If the number does not fit in the allowed space, a % is printed preceding it.

  • If there are more expressions than format fields, the format string is wrapped around.
  • Expressions may be separated with semicolons or commas; the effect is the same.
  • If the USING declaration ends in a comma or semicolon, no newline is printed at the end.
  • After a USING declaration, other elements of the PRINT syntax such as SPC( and TAB( can not be used.
Parameters
  • expr_0, expr_1, ... are expressions of any type.
  • format is a string expression that specifies the output format.
  • uexpr_0, uexpr_1, ... are expressions matching a token in the format string.
Notes
  • If an error is raised, the output before the error was encountered is printed as normal.
  • In GW-BASIC, when formatting a number with a dollar sign, if the number is in the range [-10000—-32767] and does not fit in the width of the number field, the minus sign is omitted. This is not implemented in PC-BASIC.
Errors
  • n has a string value: Type mismatch.
  • n is not in [-32768—65535]: Overflow.
  • The format string contains no tokens: Illegal function call.
  • An expression doesn't match the corresponding format token type: Type mismatch.
  • A number field in the format string exceeds 24 characters: Illegal function call.
  • A number field in the format string contains no # characters: Illegal function call.

PUT (files)

PUT [#] file_number [, record_number]

Writes a record to the random-access file file_number at position record_number.

Parameters
  • file_number is a numeric expression that yields the number of an open random-access file. The # is optional and has no effect.
  • record_number is a numeric expression in [1—33554432] (2^25) and is interpreted as the record number.
Notes
  • The record number is stored as single-precision; this precision is not high enough to distinguish single records near the maximum value of 2^25.
Errors
  • record_number is not in [1—33554432]: Bad record number.
  • file_number is not in [0—255]: Illegal function call.
  • file_number is not the number of an open file: Bad file mode.
  • file_number is open under a mode other than RANDOM: Bad file mode.
  • file_number is not specified: Missing operand.

PUT (communications)

PUT [#] com_file_number [, number_bytes]

Writes number_bytes bytes to the communications buffer opened under file number com_file_number. number_bytes is a numeric expression between 1 and the COM buffer length, inclusive.

Notes
  • In GW-BASIC, Device I/O error is raised for overrun error, framing error, and break interrupt. Device fault is raised if DSR is lost during I/O. A Parity error is raised if parity is enabled and incorrect parity is encountered. This is according to the manual; it is untested.
Errors
  • bytes is less than 1: Bad record number.
  • bytes is less than 32768 and greater than the COM buffer length: Illegal function call.
  • com_file_number is not specified: Missing operand.
  • com_file_number is not in [0—255]: Illegal function call.
  • com_file_number is not the number of an open file: Bad file number.
  • The serial input buffer is full, i.e. LOF(com_file_number) = 0 and LOC(com_file_number)=255: Communication buffer overflow.

PUT (graphics)

PUT (x0, y0), array_name [, {PSET|PRESET|AND|OR|XOR}]

Displays an array to a rectangular area of the graphics screen. Usually, PUT is used with arrays that have been stored using GET. See GET for the format of the array.

The keywords have the following effect:

PSET Overwrite the screen location with the new image
PRESET Overwrite the screen location with the inverse image
AND Combines the old and new attributes with bitwise AND
OR Combines the old and new attributes with bitwise OR
XOR Combines the old and new attributes with bitwise XOR
Parameters
  • array_name is a numeric array.
  • x0, y0 are numeric expressions.
Errors
  • The array does not exist: Illegal function call.
  • array_name refers to a string array: Type mismatch.
  • x0, y0 are string expressions: Type mismatch.
  • x0, y0 are not in [-32768—32767]: Overflow.
  • x0, y0 is outside the current VIEW or WINDOW: Illegal function call

RANDOMIZE

RANDOMIZE [expr]

Seeds the random number generator with expr. If no seed is specified, RANDOMIZE will prompt the user to enter a random seed. The user-provided value is rounded to an integer. The random seed is formed of the last two bytes of that integer or expr. If expr is a float (4 or 8 bytes), these are XORed with the preceding 2. The first 4 bytes of a double are ignored. The same random seed will lead to the same sequence of pseudorandom numbers being generated by the RND function.

Parameters
  • expr is a numeric expression.
Notes
  • For the same seed, PC-BASIC produces the same pseudorandom numbers as GW-BASIC 3.23.
  • The random number generator is very poor and should not be used for serious purposes. See RND for details.
Errors
  • expr has a string value: Illegal function call.
  • The user provides a seed outside [-32768—32767] at the prompt: Overflow.

READ

READ var_0 [, var_1] ...

Assigns data from a DATA statement to variables. Reading starts at the current DATA position, which is the DATA entry immediately after the last one read by previous READ statements. The DATA position is reset to the start by the RUN and RESTORE statements.

Parameters
  • var_0, var_1 are variables or array elements.
Errors
  • Not enough data is present in DATA statements: Out of DATA.
  • The type of the variable is not compatible with that of the data entry being read: a Syntax error occurs on the DATA line.

REM

{REM|'} [anything]

Ignores everything until the end of the line. The REM statement is intended for comments. Everything after REM will be stored in the program unaltered and uninterpreted. ' (apostrophe) is an alias for :REM'; it can be placed at any point in the program line and will ensure that the rest of the line is ignored.

Note that a colon : does not terminate the REM statement; the colon and everything after it will be treated as part of the comment.


RENUM

RENUM [new|.] [, [old|.] [, increment]]

Replaces the line numbers in the program by a systematic enumeration starting from new and increasing by increment. If old is specified, line numbers less than old remain unchanged. new, old are line numbers; the dot . signifies the last line edited. increment is a line number but must not be a dot or zero.

Notes
  • Line numbers afer the following keywords will be renumbered: AUTO, EDIT, ELSE, ERL, DELETE, GOSUB, GOTO, LIST, LLIST, RENUM, RESTORE, RESUME, RETURN, RUN, THEN.
  • Any line numbers in CHAIN statements will not be renumbered; note that these line numbers refer to another program.
  • All arguments of RENUM or AUTO statements in a program will be renumbered, including any line number offsets or increments, even though that does not make much sense.
  • A zero line number following the keywords ERROR GOTO will not be renumbered.
  • If a referenced line number does not exist in the program, a message Undefined line ref in old_line is printed. Here, old_line is the line number prior to renumbering. The referenced line number will be left unchanged, but the line's old line number will be renumbered.
Errors
  • Any of the parameters is not in [0—65529]: Syntax error.
  • Any of the newly generated line numbers is greater than 65529: Illegal function call. The line numbers up to the error have not been changed.
  • increment is empty or zero: Illegal function call.
  • old is specified and new is less than or equal to an existing line number less than old: Illegal function call.

RESET

RESET

Closes all open files.

Notes
  • Official GW-BASIC documentation and many other sources state that RESET closes all files on disk devices. However, in reality GW-BASIC 3.23 also closes files on tape and any other device, making this statement identical to CLOSE with no arguments. PC-BASIC follows this behaviour.

RESTORE

RESTORE [line]

Resets the DATA pointer. line is a line number. If line is not specified, the DATA pointer is reset to the first DATA entry in the program. If it is specified, the DATA pointer is reset to the first DATA entry in or after line.

Errors
  • line is not an existing line number: Undefined line number.

RESUME

RESUME [0|NEXT|line]

Continues normal execution after an error handling routine. If 0 or no option is specified, re-executes the statement that caused the error. If NEXT is specified, executes the statement following the one that caused the error. If line is specified, it must be a valid line number.

Errors
  • RESUME is encountered outside of an error trapping routine: RESUME without error.
  • The program ends inside an error trapping routine without a RESUME or END statement: No RESUME.
  • line is not an existing line number: Undefined line number.

RETURN

RETURN [line]

Returns from a GOSUB subroutine. If line is not specified, RETURN jumps back to the statement after the GOSUB that jumped into the subroutine. If line is specified, it must be a valid line number. RETURN jumps to that line (and pops the GOSUB stack). When returning from an error trapping routine, RETURN re-enables the event trapping which was stopped on entering the trap routine.

Errors
  • line is not an existing line number: Undefined line number.

RMDIR

RMDIR dir_spec

Removes an empty directory on a disk device.

Parameters
  • The string expression dir_spec is a valid file specification that specifies the path and name of the directory.
Errors
  • dir_spec has a numeric value: Type mismatch.
  • dir_spec is an empty string: Bad file name.
  • No matching path is found: Path not found.
  • Directory to remove is not empty: Path/File access error.

RSET

RSET string_name = expression

Copies a string value into an existing string variable or array element. The value will be right-justified and any remaining characters are replaced by spaces.

Parameters
  • string_name is a string variable or array element.
  • expression is a string expression.
Notes
  • If expression has a value that is longer than the length of the target variable, it is truncated at the tail to the length of the target variable.
  • If string_name has not been allocated before, this statement has no effect.
  • Use LSET, RSET or MID$ to copy values into a FIELD buffer.
  • If LET is used on a FIELD variable instead of L|RSET, the variable is detached from the field and a new, normal string variable is allocated.
Errors
  • string_name is not a string variable: Type mismatch.
  • expression does not have a string value: Type mismatch.


RUN

RUN [line_number [anything]|file_spec [, R]]

Executes a program. Existing variables will be cleared and any program in memory will be erased. RUN implies a CLEAR If ,R is specified after file_spec, files are kept open; if not, all files are closed.

Parameters
  • line_number is a valid line number in the current program. If specified, execution starts from this line number. The rest of the RUN statement is ignored in this case.
  • The string expression file_spec, if specified, is a valid file specification indicating the file to read the program from.
Errors
  • line_number is not a line number in the current program: Undefined line number.
  • file_spec cannot be found: File not found.
  • file_spec is an empty string: Bad file number.
  • A loaded text file contains lines without line numbers: Direct statement in file.

SAVE

SAVE file_spec [, {A|P}]

Stores the current program in a file.

  • If ,A is specified, the program will be saved in plain text format. In this case, program execution will stop and control will be returned to the user.
  • If ,P is specified, the program will be saved in protected format. When a protected program is loaded in GW-BASIC, it cannot be LISTed or SAVEd in non-protected format.
  • If neither is specified, the program will be saved in tokenised format.
Parameters
  • The string expression file_spec is a valid file specification indicating the file to store to.
Errors
  • file_spec has a number value: Type mismatch.
  • file_spec is an empty string: Bad file number.
  • file_spec contains disallowed characters: Bad file number (on CAS1:); Bad file name (on disk devices).
  • hide-protected is enabled, the current program is protected and ,P is not specified: Illegal function call.

SCREEN (statement)

SCREEN [mode] [, [colorburst] [, [apage] [, [vpage] [, erase]]]]

Change the video mode, composite colorburst, active page and visible page. Video modes are described in the Video Modes section.

Parameters
  • mode is a numeric expression that sets the screen mode.
  • colorburst is a numeric expression. See notes below.
  • apage is a numeric expression that sets the active page.
  • vpage is a numeric expression that sets the visible page.
  • erase is a numeric expression in the range [0, 1, 2]. It is only legal with syntax={pcjr, tandy}. See notes below.
Video modes

The video modes are as follows:

SCREEN 0 Text mode
80x25 or 40x25 characters of 8x16 pixels
16 attributes picked from 64 colours
Attributes 16-31 are blinking versions of 0-15
4 pages ega
SCREEN 1 CGA colour
320x200 pixels
40x25 characters of 8x8 pixels
4 attributes picked from 16 colours; 2 bits per pixel
1 page ega 2 pages pcjr tandy
SCREEN 2 CGA monochrome
640x200 pixels
80x25 characters of 8x8 pixels
2 attributes picked from 16 colours; 1 bit per pixel
1 page ega 2 pages pcjr tandy
SCREEN 3 Low-res 16-colour pcjr tandy
160x200 pixels
20x25 characters of 8x8 pixels
16 attributes picked from 16 colours; 4 bits per pixel
2 pages
SCREEN 3 Hercules monochrome hercules
720x348 pixels
80x25 characters of 9x14 pixels (with bottom line truncated by 2 px)
2 attributes; 1 bit per pixel
2 pages
SCREEN 3—255 Altissima risoluzione olivetti
640x400 pixels
80x25 characters of 8x16 pixels
2 attributes of which one picked from 16 colours; 2 bits per pixel
1 page
SCREEN 4 Med-res 4-colour pcjr tandy
320x200 pixels
40x25 characters of 8x8 pixels
4 attributes picked from 16 colours; 2 bits per pixel
2 pages
SCREEN 5 Med-res 16-colour pcjr tandy
320x200 pixels
40x25 characters of 8x8 pixels
16 attributes picked from 16 colours; 4 bits per pixel
1 page

Note: a minimum of 32768 bytes of video memory must be reserved to use this video mode. Use the statement CLEAR ,,,32768! or the option video-memory=32768.

SCREEN 6 High-res 4-colour pcjr tandy
640x200 pixels
80x25 characters of 8x8 pixels
4 attributes picked from 16 colours; 2 bits per pixel
1 page

Note: a minimum of 32768 bytes of video memory must be reserved to use this video mode. Use the statement CLEAR ,,,32768! or the option video-memory=32768.

SCREEN 7 EGA colour ega
320x200 pixels
40x25 characters of 8x8 pixels
16 attributes picked from 16 colours; 4 bits per pixel
8 pages
SCREEN 8 EGA colour ega
640x200 pixels
80x25 characters of 8x8 pixels
16 attributes picked from 16 colours; 4 bits per pixel
4 pages
SCREEN 9 EGA colour ega
640x350 pixels
80x25 characters of 8x14 pixels
16 attributes picked from 64 colours; 4 bits per pixel
2 pages
SCREEN 10 EGA monochrome ega monitor=mono
640x350 pixels
80x25 characters of 8x14 pixels
4 attributes picked from 9 pseudocolours; 2 bits per pixel
2 pages
NTSC Composite Colorburst

On CGA, Tandy and PCjr, colorburst has the following effects, depending on the type of monitor - RGB (default) or composite:

mode colorburst CGA mode Effect (composite) Effect (RGB)
0 0 0, 2 greyscale default palette
0 1 1, 3 colour default palette
1 0 4 colour default palette
1 1 5 greyscale alternate palette

On SCREEN 2, colorburst has no effect; on a composite monitor, colour artifacts can be enabled on this screen through OUT (see there). On SCREEN 3 and up, colorburst has no effect.

Erase

By default, if the mode changes or the colorburst changes between zero and non-zero, the old page and the new page of the screen are cleared. On syntax={pcjr, tandy}, the erase parameter can be used to change this behaviour. Its values are as follows:

erase Effect
0 Do not erase any screen page
1 (default) If the mode changes or the colorburst changes between zero and non-zero, the old page and the new page of the screen are cleared.
2 If the mode changes or the colorburst changes between zero and non-zero, all pages of the screen are cleared.
Notes
  • At least one parameter must be specified.
  • Composite colour artifacts are emulated only crudely in PC-BASIC, and not at all in SCREEN 1.
Errors
  • No parameters are specified: Missing operand.
  • Any parameter has a string value: Type mismatch.
  • Any parameter is not in [-32768—32767]: Overflow.
  • mode is not an available video mode number for your video card setting: Illegal function call.
  • vpage, apage are not between 0 and the number of pages for the chosen video mode, less one: Illegal function call.
  • colorburst is not in [0—255]: Illegal function call.
  • erase is not in [0, 1, 2]: Illegal function call.

SHELL

SHELL [command]

Starts an operating system subshell on the console. If command is specified, the command is executed on the shell and execution returns to the program.

To enable this statement, the shell option must be set to a valid command interpreter.

Parameters
  • command is a string expression.
Notes
  • Be careful when enabling this command, as it allows the running BASIC program full access to your files and operating system.
Errors
  • shell option is not specified: Illegal function call.
  • command has a number value: Type mismatch.
  • All output from the operating system subshell, including error messages, is displayed on the PC-BASIC screen.

SOUND (tone)

SOUND frequency, duration [, volume [, voice]]

Produces a sound at frequency Hz for duration/18.2 seconds. On PCjr and Tandy, the volume and voice channel can additionally be specified.

If PLAY "MB" has been executed, SOUND plays in the background. If PLAY "MF" has been executed, sound plays in the foreground and the interpreter blocks until the sound is finished. Foreground mode is default. Unlike PLAY, the sound played by the most recent SOUND statement always plays in the background, even if PLAY "MF" has been entered. In background mode, each SOUND statement counts as 1 toward the length of the queue reported by the PLAY function.

Parameters
  • frequency is a numeric expression in [37—32767] or 0 (for syntax={advanced | pcjr}) or in [-32768—32767] (for syntax=tandy).
  • duration is a numeric expression in [0—65535].
  • volume is a numeric expression in [-1—15]. 0 is silent, 15 is full volume; every step less reduces the volume by 2 dB. -1 is also full volume. (For syntax={pcjr | tandy}).
  • voice is a numeric expression in [0—2], indicating which of the three tone voice channels is used for this sound. (For syntax={pcjr | tandy})
Notes
  • On PCjr and Tandy, Frequencies below 110 Hz are played as 110 Hz.
  • If duration is zero, any active background sound is stopped and the sound queue is emptied.
  • If duration is zero, volume and voice must not be specified.
  • If duration is less than .022 but nonzero, the sound will be played in background and continue indefinitely until another sound statement is executed. This is also the behaviour for negative duration.
  • If frequency equals 32767 or 0, a silence of length duration is queued.
Errors
  • Any argument has a string value: Type mismatch.
  • frequency is not in its allowed range, and duration is not zero: Illegal function call.
  • duration is zero and more than two arguments are specified: Syntax error.
  • syntax={ pcjr | tandy } is not set and more than two arguments are specified: Syntax error.
  • frequency is not in [-32768—32767]: Overflow.
  • duration is not in [-65535—65535]: Illegal function call.
  • volume is not in [0—15]: Illegal function call.
  • voice is not in [0—2]: Illegal function call.

SOUND (switch)

SOUND {ON|OFF}

Switches the external speaker on or off and toggles the availability of advanced sound capabilities on PCjr and Tandy. This includes 3-voice sound, noise generation and volume control. Clears the background music queue.

Notes
  • Only available with syntax={pcjr | tandy}.
  • On PC-BASIC, both the internal and the external speaker are emulated through the same sound system.
Errors
  • This statement is used and syntax={ pcjr | tandy } is not set: Syntax error.

STOP

STOP

Breaks program execution, prints a Break message on the console and returns control to the user. Files are not closed. It is possible to resume program execution at the next statement using CONT.


STRIG (switch)

STRIG {ON|OFF}

Has no effect.


STRIG (event switch)

STRIG[ ](button) {ON|OFF|STOP}

Switches event trapping of the joystick trigger button ON or OFF. STRIG (button) STOP suspends event trapping until STRIG (button) ON is executed. Up to one event can be triggered during suspension, provided that event handling was switched on prior to suspension. The event triggered during suspension is handled immediately after the next STRIG (button) ON statement.

button return value
0 1st joystick 1st trigger
2 2nd joystick 1st trigger
4 1st joystick 2nd trigger
6 2nd joystick 2nd trigger
Parameters
  • button is a numeric expression in [0, 2, 4, 6].
Errors
  • button has a string value: Type mismatch.
  • button is not in [-32768—32767]: Overflow.
  • button is not in [0, 2, 4, 6]: Illegal function call.

SWAP

SWAP var_0, var_1

Exchanges variables var_0 and var_1.

Notes
  • The variables are exchanged by reference. If, for example, var_0 is a FIELD variable and var_1 is not, then SWAP will reverse those roles.
Parameters
  • var_0 and var_1 are variables or array elements of the same type. var_1 must have been previously defined.
Errors
  • var_1is undefined: Illegal function call. Note that no error is raised if var_0 is undefined, and that after this error both variables will be defined.
  • The types of var_0 and var_1 are not the same: Type mismatch.

SYSTEM

SYSTEM

Exits the interpreter.

Notes
  • SYSTEM quits the PC-BASIC interpreter immediately without further interaction. Any unsaved program or data will be lost.

TERM

TERM

Load and run the program defined by the term option. By default, as on the IBM PCjr, this is a built-in serial terminal emulator application. This statement is only available with syntax={pcjr|tandy}.

Errors
  • If term is not set, this statement raises Internal error.
  • If syntax is not set to pcjr or tandy, this keyword is not present. Calling TERM will raise Syntax error.

TIME$ (statement)

TIME$ = time

Sets the current BASIC time to time.

Parameters
  • Time is a string expression of the form "HH{:|.}mm{:|.}ss" where 0 <= HH < 24, 0 <= mm < 60 and 0 <= ss < 60. Each position may have one or two characters.
Notes
  • PC-BASIC stores an offset to the system time and uses this for future calls to TIME$ and DATE$ functions in the same interpreter session. The system time is not changed, unlike GW-BASIC under MS-DOS.
Errors
  • time has a numeric value: Type mismatch.
  • time is not of the correct form: Illegal function call.

TIMER (statement)

TIMER {ON|OFF|STOP}
  • ON: enables ON TIMER event trapping of the timer clock.
  • OFF: disables trapping.
  • STOP: halts trapping until TIMER ON is used. Events that occur while trapping is halted will trigger immediately when trapping is re-enabled.

TRON and TROFF

{TRON|TROFF}

Turns line number tracing on or off. If line number tracing is on, BASIC prints a tag [100] to the console when program line 100 is executed, and so forth.

Notes
  • Tracing is turned off by the NEW and LOAD statements.

UNLOCK

UNLOCK [#] file_number [, record_0] UNLOCK [#] file_number, [record_0] TO record_1

Unlocks a file or part of it that has previously been locked with LOCK.

Parameters
  • file_number is a numeric expression in [0—255].
  • record_0 and record_1 are numeric expressions in [1—2^25-2].
Errors
  • Any parameter has a string value: Type mismatch.
  • file_number is not in [-32768—32767]: Overflow.
  • file_number is not in [0—255]: Illegal function call.
  • file_number is not an open file: Bad file number.
  • If file_number is open for RANDOM, LOCK and UNLOCK statements must match in terms of record_0 and record_1. An non-matching UNLOCK will raise Permission denied.
  • record_0 or record_1 is not in [1—2^25-2]: Bad record number.

VIEW

VIEW [[SCREEN] (x0, y0)-(x1, y1) [, [fill] [, border]]]

Defines a graphics viewport. Graphics drawn outside the viewport will not be shown. (x0, y0), (x1, y1) are absolute screen coordinates of two opposing corners of the area.

Unless SCREEN is specified, after a VIEW statement the coordinate system is shifted such that (0, 0) becomes the top left coordinate of the viewport. If VIEW is called without arguments, the viewport is reset to the whole screen.

Parameters
  • fill is an attribute. The viewport will be filled with this attribute.
  • border is an attribute. A border will be drawn just outside the viewport with this attribute.
Errors
  • Any of the parameters has a string value: Type mismatch.
  • Any of the coordinates is not in [-32768—32767]: Overflow.
  • Any of the coordinate pairs is outside the physical screen: Illegal function call.

VIEW PRINT

VIEW PRINT top_row TO bottom_row

Defines the text scrolling area of the screen. LOCATE statements, cursor movement and scrolling will be limited to the scrolling area.

Parameters
  • top_row and bottom_row are numeric expressions in [1—24].
Notes
  • If syntax={pcjr | tandy} and KEY OFF is set, bottom_row may be 25. Otherwise, screen row 25 cannot be part of the scrolling area.
Errors
  • top_row or bottom_row is not in [1—24]: Illegal function call.

WAIT

WAIT port, and_mask [, xor_mask]

Waits for the value of (INP(port) XOR xor_mask) AND and_mask to become nonzero. Event handling is suspended until WAIT returns. If xor_mask is not specified, it defaults to 0.

Notes
  • A limited number of machine ports are emulated in PC-BASIC. See INP.
Errors
  • Any parameter has a string value: Type mismatch.
  • port is not in [-32768—65535]: Overflow.
  • and_mask or xor_mask are not in [0—255]: Type mismatch.

WEND

WEND

Iterates a WHILE—WEND loop: jumps to the matching WHILE statement, where its condition can be checked.

Notes
  • WHILE—WEND loops can be nested. WEND jumps to the most recent WHILE statement that has not been closed by another WEND.
Errors
  • All previous WHILE statements have been closed by another WEND or no WHILE statement has been executed before: WEND without WHILE.

WHILE

WHILE expr

Initiates a WHILE—WEND loop. If expr evaluates to zero, WHILE jumps to the statement immediately after the matching WEND. If not, execution continues.

Parameters
  • expr is a numeric expression.
Errors
  • No matching WEND is found: WHILE without WEND.
  • expr has a string value: Type mismatch.

WIDTH (console)

WIDTH num_columns [, [num_rows] [,]]

Sets the screen width to 20, 40 or 80 columns.

Notes
  • When changing screen width in graphics mode, the video mode is changed. The following changes occur:
    SCREEN 1 (40) ↔ SCREEN 2 (80)
    SCREEN 7 (40) ↔ SCREEN 8 (80)
    SCREEN 7 (40) ← SCREEN 9 (80)
  • Screen width value 20 is only allowed on Tandy and PCjr. Changing to this width changes to SCREEN 3. Additionally, the following changes occur:
    SCREEN 3 (20) → SCREEN 1 (40)
    SCREEN 3 (20) → SCREEN 2 (80)
    SCREEN 4 (40) → SCREEN 2 (80)
    SCREEN 5 (40) ↔ SCREEN 6 (80)
Parameters
  • num_columns is either a literal 20, 40 or 80 or a numeric expression in parentheses. The trailing comma is optional and has no effect.
  • num_rows is optional and must equal 25. If syntax={pcjr | tandy} is set, num_rows may be in [0—25] but its value is ignored.
Errors
  • num_columns is a string expression: Type mismatch.
  • num_columns is not in [-32768—32767]: Overflow.
  • num_columns is not in [0—255]: Illegal function call.
  • num_columns is not a literal and not bracketed: Illegal function call.
  • num_rows is not in its accepted range: Illegal function call.

WIDTH (devices and files)

WIDTH {#file_num,|device_name,|LPRINT} num_columns

Sets the line width for a file or a device. When a write operation passes beyond the column width, a CR LF sequence is inserted.

If a device is specified, it does not need to have a file open to it; the width setting will be the default width next time a file is opened to that device.

If device_name is "LPT1:" or LPRINT is specified, the device width setting affects LPRINT and LLIST.

If device_name is "SCRN:", "KYBD:", or omitted, the screen width is changed. In this case, num_columns must be one of 20, 40 or 80. See the notes at WIDTH (console) for side effects.

Parameters
  • file_num is a numeric expression which is the number of an open file.
  • device_name is a string expression that is one of "KYBD:", "SCRN:", "LPT1:", "LPT2:", "LPT3:", "COM1:", "COM2:", "CAS1:"
  • num_columns is a numeric expression.
Errors
  • device_name is not one of the allowed devices: Bad file name.
  • device_name is "SCRN:", "KYBD:" and num_columns is not 20, 40 or 80: Illegal function call.
  • file_num or num_columns are strings: Type mismatch.
  • file_num or num_columns are not in [-32768—32767]: Overflow.
  • file_num or num_columns are not in [0—255]: Illegal function call.
  • file_num is not an open file: Bad file mode.

WINDOW

WINDOW [[SCREEN] (x0, y0)-(x1, y1)]

Define logical coordinates for the viewport. If SCREEN is not specified, the bottom left of the screen is mapped to the lower coordinates; the top right of the screen is mapped to the higher coordinates. If SCREEN is specified, the top left of the screen is mapped to the lower coordinates; the bottom right of the screen is mapped to the higher coordinates.

If WINDOW is called without arguments, the logical coordinates are reset to the viewport coordinates.

Parameters
  • x0, y0, x1, y1 are numeric expressions.
Errors
  • Any of the coordinates have a string value: Type mismatch.
  • x0 = x1 or y0 = y1: Illegal function call.

WRITE

WRITE [# file_num,] [expr_0 [{,|;} expr_1] ... ]

Writes values to a file or the screen in machine-readable form. Values are separated by commas and the line is ended with a CR LF sequence. Strings are delimited by double quotes ". No padding spaces are inserted.

When writing to the screen, the same control characters are recognised as for the PRINT statement.

Parameters
  • expr_0, expr_1, ... are expressions whose value is to be printed.
Errors
  • file_num has a string value: Type mismatch.
  • file_num is open for INPUT: Bad file mode.


Errors and Messages

Errors

1 NEXT without FOR

A NEXT statement has been encountered for which no matching FOR can be found.

2 Syntax error

The BASIC syntax is incorrect. A statement or expression has been mistyped or called in one of many incorrect ways. This error is also raised on a DATA line if a READ statement encounters a data entry of an incorrect format.

3 RETURN without GOSUB

A RETURN statement has been encountered for which no GOSUB call has been made.

4 Out of DATA

A READ statement is attempting to read more data entries than can be found from the current DATA location onward.

5 Illegal function call

A statement, function or operator has been called with parameters outside the accepted range. This error is also raised for a large variety of other conditions – check the reference for the statement or function called.

6 Overflow

A numeric expression result or intermediate value is too large for the required number format.

7 Out of memory

There is not enough free BASIC memory to complete the operation. Too much memory is consumed by the program; variables, arrays and strings, or execution stacks for loops, subroutines or user-defined functions.

8 Undefined line number

A reference is made to a line number that does not exist in the program.

9 Subscript out of range

An array index (subscript) is used that is outside the range reserved for that array by the DIM statement.

10 Duplicate Definition

A DIM statement is used on an array that has been dimensioned before (either implicitly or explicitly) or OPTION BASE is called in a way that conflicts with an earlier implicit or explicit definition of the starting index.

11 Division by zero

An attempt is made to divide a number by zero or by a number that is too small to distinguish from zero within the number format's precision.

12 Illegal direct

A DEF FN statement is being used in direct mode.

13 Type mismatch

The expression used is of a type that cannot be converted to the required type for the function or statement. Most commonly, this is raised if a string argument is supplied to a statement or function that expects a number, or vice versa.

14 Out of string space

There is not enough free BASIC memory to store the string variable.

15 String too long

A string expression result or intermediate value is longer than 255 characters.

16 String formula too complex
17 Can't continue

The CONT statement is used in circumstances where continuing program execution is not possible.

18 Undefined user function

The FN function is called with a function name for which no definition was made by a DEF FN statement.

19 No RESUME

The program terminates inside an error trapping routine that has not been closed with RESUME or END.

20 RESUME without error

A RESUME statement is encountered while the program is not executing an error trapping routine.

21unused
22 Missing operand

An operator expression misses an operand or a function or statement is not supplied with sufficient parameters.

23 Line buffer overflow

An INPUT or LINE INPUT statement encountered an input string longer than 255 characters or the plain-text program file being loaded by LOAD, CHAIN or MERGE contains a line with more than 255 characters. Attempting to load a text file that has LF rather than CR LF line endings may cause this error.

24 Device Timeout

The handshake has failed on a serial device or a tape device has reached the end of tape.

25 Device Fault
26 FOR without NEXT

A FOR statement has been encountered for which no matching NEXT statement can be found.

27 Out of paper

An attempt is made to write to a printer which is out of paper or to another parallel device which has raised an out-of-paper condition.

28 unused
29 WHILE without WEND

A WHILE statement has been encountered for which no matching WEND statement can be found.

30 WEND without WHILE

A WEND statement has been encountered for which no matching WHILE statement can be found.

31—49unused
50 FIELD overflow

An attempt is made to read, write, or define a FIELD variable beyond the length of the random-access file buffer.

51 Internal error

The TERM statement is executed but no terminal manager program has been defined.

52 Bad file number

A file number is accessed to which no file is open, or the file number used in an OPEN statement is outside the range of allowable file numbers, or (confusingly) the file specification is empty, malformed or contains illegal characters.

53 File not found

A named file on a disk device cannot be found.

54 Bad file mode

The requested file mode in an OPEN statement does not exist or is unsupported for the given device, or the file function called is not supported for this device, or the function or statement called requires a file opened for RANDOM and the file is not.

55 File already open

An attempt is made to open a file to a file number that is already in use; or an attempt is made to open a file for OUTPUT or APPEND on a serial, disk or cassette device when a file (or, on a disk device, a file with the same name) is already open for OUTPUT or APPEND on that device; or a KILL or NAME statement is executed on a disk file when a file with the same name is open on the same device.

56 unused
57 Device I/O error

An I/O error has occured during input/output to a device. This includes faming errors, CRC check failures and unexpected end-of-tape on cassette devices.

58 File already exists

The proposed new name of a disk file in a NAME statement is already in use.

59—60 unused
61 Disk full

There is insufficient free space on the disk device to complete the operation.

62 Input past end

An attempt is made to retrieve input from a file that has passed its end of file.

63 Bad record number

A random-access file record number is referenced that is outside the permitted range.

64 Bad file name

The file name or other device parameter string in a file specification is malformed or contains illegal characters.

65 unused
66 Direct statement in file

A line with no line number is encountered in a plain-text program file.

67 Too many files
68 Device Unavailable

An attempt is made to access a device that does not exist or is not enabled.

69 Communication buffer overflow

A serial device is receiving more data than fits in its buffer.

70 Permission Denied

The requested access to a file is not granted due to LOCK restrictions, operating system locking, or insufficient operating system file permissions.

71 Disk not Ready

The disk device is not ready for access. For example, there is no diskette in a floppy drive or the drive lock is open.

72 Disk media error
73 Advanced Feature
74 Rename across disks

An attempt is made to use the NAME statement to move a file from one disk device to another.

75 Path/File access error

An attempt is made to create a directory that already exists or to remove a directory that is not empty.

76 Path not found

An OPEN, MKDIR, RMDIR, or CHDIR statement is executed referring to a (parent) path that does not exist on the disk device.

77 Deadlock

Any error code that does not have a message associated to it will generate the message Unprintable error.

If an error occurs in direct mode, the error message is printed as above. If the error occurs in a program, the message is supplemented with the line number in which the error occurred. For example, Illegal function call in 100 indicates that the illegal function call took place in line number 100.

If a Syntax error occurs during program execution, the error message is followed by a listing of the program line in which the error occurred, wth the cursor positioned at the location where the error was raised.

A Division by zero error or, in a floating point calculation, an Overflow, will not interrupt execution unless it occurs within an error handling routine. The error message will be printed on the console and the result of the offending calculation will be taken to be the maximum value that fits in the appropriate floating-point variable. Overflow in an integer calculation will always interrupt execution like other errors.

Other messages

Break
Execution of a compound statement or program has been interrupted by a CONT statement or by a user keyboard interrupt (such as Ctrl+Break). If the interrupt happens in a program, the Break message will be supplemented with the line number in which the interrupt occurred.
?Redo from start
The input provided on the console for an INPUT statement does not match the expected format. The number or type of inputs is not correct. Re-enter all inputs.
Undefined line ref_num in line_num
The RENUM statement encountered a reference to the line number ref_num which is not defined in the program. The reference occurs on line number line_num. The undefined line number reference will not be renumbered.
filename Found.
A file matching the requested specification has been found on the cassette device. This message only occurs in direct mode.
filename Skipped.
A file not matching the requested specification has been encountered on the cassette device. This message only occurs in direct mode.