BASIC LANGUAGE SYNTAX

 

How to Use This Material

 

Descriptions of some of the BASIC language statements and functions are described in this appendix.  The entries are arranged alphabetically.

 

The description of each statement and function is formatted as follows:

 

Purpose:

Tells what the statement or function does.

 

Format:

Shows the correct format for the statement or function.  Keep the following rules in mind:

 

·        Words in capital letters are keywords and must be entered as shown, except that they can be entered in any combination of uppercase and lowercase letters.  BASIC automatically converts letters to uppercase unless they are enclosed in quote marks.

·        You are to supply any items shown in lowercase italic letters.

·        Items in square brackets ([ ]) are optional.

·        An ellipsis (…) indicates that an item can be repeated as many times as you wish.

·        All punctuation except square brackets (such as commas, parentheses, semicolons, hyphens or equal signs) must be included where shown.

 

Remarks:

Describes in detail how to use the statement or function.

 

Example:

Shows sample programs, or program segments that demonstrate the use of the statement or function.

 

ABS

Function

 


Purpose:    

Returns the absolute value of the expression x.

 

 

Format:

v = ABS(x)

 

 

Remarks:

x     can be any numerical expression.

 

The absolute value of a number is always positive or zero.

 

 

Example:

This example shows that the absolute value of -35 is positive 35.

 

PRINT  ABS(7*(-5))

 35

 

 

ASC

Function

 


Purpose:    

Returns the ASCII code of the first character in string (x$).

 

 

Format:

v = ASC(x$)

 

 

Remarks:

x$      can be any string expression.

 

The result of the ASC function is a numerical value that is the ASCII code of the first character of the string x$.  If x$ is null, an "illegal function call" error is returned.

 

 

Example:

This example shows that the ASCII code for capital "T" is 84.  PRINT  ASC("TEST") would work just as well.

 

10 X$  =  "TEST"

20 PRINT ASC(X$)

RUN

 84

 

 

 

 

CHR$

Function

 


Purpose:    

Converts an ASCII code to its character equivalent.

 

 

Format:

v$= CHR$(n)

 

 

Remarks:

n must be in the range 0 to 255.

 

The CHR$ function returns the one-character string with ASCII code n.  CHR$ is commonly used to send a special character to the screen or printer.  For example, the BEL character, which beeps the speaker, might be included as CHR$(7) as the preface to an error message.

 

 

Example:

This example prints the character equivalent of ASCII code 66.

 

PRINT  CHR$(66)

B

 

 

DATA

Statement

 


Purpose:    

Stores the numeric and string constants that are accessed by a program's READ statement.

 

 

Format:

DATA constant{,constant}…

 

 

Remarks:

constant     can be a numeric or string constant.  No expressions are allowed in the list.  The numeric constants can be in any format: integer, fixed point, floating point, hex, or octal.  String constants in DATA statements do not have to be enclosed by quotation marks, unless the string contains commas, colons, or significant leading or trailing blanks.

 

DATA statements are nonexecutable and can be placed anywhere in the program.  A DATA statement can contain as many constants as will fit on a line, and any number of DATA statements can be used in a program.  The READ statement accesses the DATA statements in line-number order.

The variable type (numeric or string( must agree with the corresponding constant in the DATA statement or a "Syntax error" occurs.

 

You may only use a :REM to add remarks to DATA statements.

 

Use the RESTORE statement to reread information from any line in the list of DATA statements.

 

 

Example:

See examples under the READ statement.

 

DIM

Statement

 


Purpose:    

Specifies the maximum values for array variable subscripts and allocates storage accordingly.

 

 

Format:

DIM variable(subscripts)[,variable(subscripts)]…

 

 

Remarks:

variable        is the name used for the array.

 

subscripts    is a list of numeric expressions, separated by commas, which define the dimensions of the array.

 

When executed, the DIM statement sets all the  elements of the specified numeric arrays to an initial value of zero.  String array elements are all variable length, with an initial value of null value (zero length).

 

The first array subscript is zero unless changed by using the "OPTION BASE 1" statement which changes the first array subscript to 1.  This must be done before the array is dimensioned.

 

 

Example:

 

 

 

 

Example:

This creates an array named XRAY that has 10 subscripts, 0 through 9.

 

10 DIM  XRAY(9)

 

This creates a two-dimensional array named TOAD that has 10 rows (0 through 9) and 10 columns (0 through 9).

 

20  DIM TOAD(9,9)

 

END

Statement

 


Purpose:    

Terminates program execution, closes all files, and returns to the command level.

 

 

Format:

END

 

 

Remarks:

END statements can be placed anywhere in the program to terminate execution.  An END statement at the end of a program is optional but is always good practice.

 

 

Example:

This example ends the program after all the instructions have been executed.

 

100 PRINT "This is an example of an END statement:

199 END

 

 

FOR and NEXT

Statements

 


Purpose:    

Performs a series of instructions in a loop a given number of times.

 

 

Format:

FOR variable = x TO y [STEP z]

   .

   .

   .

NEXT [variable [,variable]…]

 

 

Remarks:

variable    is an integer variable used as a counter.

 

x               is a numeric expression that is the initial value of the counter.

 

y               is a numeric expression that is the final value of the counter.

 

z               is a numeric expression to be used as an increment.  The default is 1 if omitted.

 

The program lines following the NEXT statement are executed in order until the NEXT statement is encountered.  Then the counter is incremented by the amount specified by the STEP value (z).  A check is performed to see if the counter is now greater than the maximum value in y.  If the counter is greater than the maximum then the statement following the NEXT is executed else the loop is re-started at the statement following the FOR.

 

The NEXT statement in the form:

 

NEXT  var1, var2, var3,…

 

is equivalent to the sequence of statements:

 

NEXT var1

NEXT var2

NEXT var3

   etc.

 

 

 

 

Example:

This example shows a loop that executes 10 times.

 

10  FOR  T  =  1  TO  5

20         PRINT  T  *  2;

30  NEXT  T

40  PRINT "The end"

RUN

2   4   6   8   10   The end

 

 

GOSUB and RETURN

Statements

 


Purpose:    

Branches to and returns from a subroutine.

 

 

Format:

GOSUB  line number at the REM statement

   .

   .

REM "Start of some subroutine"

   .

   .

RETURN

 

 

 

Remarks:

line     is the line number of the first line in some subroutine.

 

RETURN causes control to be transferred back to the statement following the GOSUB statement..

 

 

Example:

This example the GOSUB at line 10 calls the subroutine at line 40.  The RETURN at line 50 causes control to go back to line 20.

 

10 GOSUB 40

20 PRINT "Back from routine"

30 END

40 PRINT "Subroutine in progress"

50 RETURN

RUN

Subroutine in progress

Back from subroutine

 

 

 

 

GOTO

Statement

 


<

Purpose:    

Branches unconditionally out of the normal program sequence to a specified line number.

 

 

Format:

GOTO line