The repeat .. until construct is termed a post-test loop, because the controlling condition is tested after each iteration of the loop.
It has the following syntax:
repeat statement1; // statement2; // further statements... until BooleanExpression;
A repeat loop encloses its executed statements, which means they do not need to be further enclosed in a begin ... end block. Note that a repeat loop continues until its controlling Boolean expression is TRUE; whereas the while loop continues until its Boolean expression is FALSE.
Use a REPEAT loop when the looping statement(s) must execute at least once, whatever the initial value of the controlling Boolean condition.