GWBASIC User's Manual

GW-BASIC User's Guide
IF ... THEN ... ELSE Statement
Purpose:
To make a decision regarding program flow based on the result returned by an expression.
Syntax:
IF expression[,] THEN statement(s)[,][ELSE statement(s)]
IF expression[,] GOTO line number[[,] ELSE statement(s)]
Comments:
If the result of expression is nonzero (logical true), the THEN or GOTO line number is executed.
If the result of expression is zero (false), the THEN or GOTO line number is ignored and the
ELSE line number, if present, is executed. Otherwise, execution continues with the next
executable statement. A comma is allowed before THEN and ELSE.
THEN and ELSE may be followed by either a line number for branching, or one or more
statements to be executed.
GOTO is always followed by a line number.
If the statement does not contain the same number of ELSE's and THEN's line number, each ELSE
is matched with the closest unmatched THEN. For example:
IF A=B THEN IF B=C THEN PRINT "A=C" ELSE PRINT "A < > C"
will not print "A < > C" when A < > B.
If an IF...THEN statement is followed by a line number in the direct mode, an "Undefined
line number" error results, unless a statement with the specified line number was previously
entered in the indirect mode.
Because IF ..THEN...ELSE is all one statement, the ELSE clause cannot be on a separate line.
It must be all on one line.
Nesting of IF Statements
IF...THEN...ELSE statements may be nested. Nesting is limited only by the length of the line.
For example, the following is a legal statement:
100 IF X > Y THEN PRINT "GREATER" ELSE IF Y > X THEN&
110 PRINT "LESS THAN"
200 ELSE PRINT "EQUAL"
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