Pascal - Repeat-Until Loop

Unlike for and while loops, which test the loop condition at the top of the loop, the repeat ... until loop in Pascal checks its condition at the bottom of the loop.

A repeat ... until loop is similar to a while loop, except that a repeat ... until loop is guaranteed to execute at least one time.

Syntax

repeat
   S1;
   S2;
   ...
   ...
   Sn;
until condition;

For example,

repeat
   sum := sum + number;
   number := number - 2;
until number = 0;

Notice that the conditional expression appears at the end of the loop, so the statement(s) in the loop execute once before the condition is tested.

If the condition is false, the flow of control jumps back up to repeat, and the statement(s) in the loop execute again. This process repeats until the given condition becomes true.

Flow Diagram

Example

program repeatUntilLoop;
var
   a: integer;

begin
   a := 10;
   (* repeat until loop execution *)
   repeat
      writeln('value of a: ', a);
      a := a + 1
   until a = 20;
end.

When the above code is compiled and executed, it produces the following result −

value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19