IF...THEN...ELSE/IF...GOTO¶

Syntax¶

IF <expression> THEN <statement(s)> | <line number>
                [ELSE <statement(s)> | <line number>]

IF <expression> GOTO <line number>
                [ELSE <statement(s)> | <line number>]

Versions: 8K, Extended, Disk

NOTE: The ELSE clause is allowed only in Extended and Disk versions.

Purpose¶

To make a decision regarding program flow based on the result returned by an expression.

Remarks¶

The IF...THEN...ELSE statement executes statements conditionally based on the evaluation of an expression.

Expression Evaluation:¶

If expression is true (non-zero), THEN clause executes
If expression is false (zero), ELSE clause executes (if present)
Expression can be numeric or use relational/logical operators

Forms:¶

IF...THEN statement - Execute statement if true
IF...THEN line_number - Jump to line if true
IF...GOTO line_number - Same as THEN line_number
IF...THEN...ELSE - Execute different code for true/false

Multiple Statements:¶

Use colon to separate multiple statements in THEN or ELSE clause:

IF X > 0 THEN A = 1 : B = 2 : PRINT "Positive"

Nested IF:¶

IF X > 0 THEN IF Y > 0 THEN PRINT "Both positive"

Examples:¶

10 INPUT "Enter a number: "; N
20 IF N > 0 THEN PRINT "Positive" ELSE PRINT "Non-positive"
30 IF N = 0 GOTO 100
40 PRINT "Not zero"

Notes:¶

ELSE must be on the same line as IF...THEN
Cannot use GOTO between THEN and ELSE
Expression is evaluated left to right