The REPEAT loop is different from the WHILE loop because the break-off condition is checked only after the loop has been executed. This means that the loop will run through at least once, regardless of the wording of the break-off condition.
Syntax:
REPEAT
<Instructions>
UNTIL <Boolean expression>
END_REPEAT;
The <Instructions> are carried out until the <Boolean expression> returns TRUE.
If <Boolean expression> is produced already at the first TRUE evaluation, then <Instructions> are executed only once. If <Boolean_expression> never assumes the value TRUE, then the <Instructions> are repeated endlessly which causes a relative time delay.
The programmer must make sure that no endless loop is caused. He does this by changing the condition in the instruction part of the loop, for example by counting up or down one counter.
Example:
REPEAT
Var1 := Var1*2;
Counter := Counter-1;
UNTIL
Counter=0
END_REPEAT;