Description

The WHILE instruction has the effect that a sequence of instructions will be executed repeatedly until its related Boolean expression is 0 (false). If the expression is false right from the start, the group of instructions will not be executed at all.

The DO instruction identifies the end of the repeat definition and the beginning of the instruction(s).

The occurrence may be terminated early using the EXIT.

The END_WHILE instruction marks the end of the instruction(s).

In the following cases WHILE may not be used as it can created an endless loop which causes the program to crash:

• WHILE may not be used for synchronization between processes, e.g. as a "Waiting Loop" with an externally defined end condition.

• WHILE may not be used in an algorithm, as the completion of the loop end condition or execution of an EXIT instruction can not be guaranteed.

Example WHILE...DO...END_WHILE

x := 1;
WHILE x <= 100 DO
        x := x + 4;
END_WHILE ;

See Also

EXIT