WHILE expression
    statements
ENDWHILE

Executes the block while expression evaluates to true.
The test happens before each iteration, so the body may execute zero times.

Remarks: WHILE must be closed with ENDWHILE.

Note: The spaced form END WHILE is not recognised.

Behaviour

ENDWHILE matches the nearest unmatched WHILE.
Loops may be nested freely.
The condition expression is re-evaluated every iteration.
If the condition never becomes false, the loop will run forever (until an error or external break).

Note: Make sure something inside the loop changes the values used by expression, or the loop will never terminate.

Examples

Simple count

N = 0
WHILE N < 3
    PRINT "N = "; N
    N = N + 1
ENDWHILE
PRINT "Done"

Zero-iteration case (condition false at start)

X = 10
WHILE X < 0
    PRINT "This never prints"
ENDWHILE
PRINT "X was not less than 0"

Nested loops

PRINT "START"
N = 0
WHILE N < 3
    PRINT "OUTER N = "; N
    O = 0
    WHILE O < 2
        PRINT "INNER O = "; O
        O = O + 1
    ENDWHILE
    N = N + 1
ENDWHILE
PRINT "LOOPS DONE"

Notes

Use REPEAT ... UNTIL if you need a post-test loop that runs the body at least once.
The condition is a normal boolean expression; use comparisons like =, <>, <, >, <=, >= and combine them with your available operators.

See also:
REPEAT · ENDIF