Swift - do...while Loop

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

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


The syntax of a repeat...while loop in Swift 4 is −

repeat {
while( condition );

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

The number 0, the strings '0' and "", the empty list(), and undef are all false in a Boolean context and all other values are true. Negation of a true value by ! or not returns a special false value.

Flow Diagram

Repeat-While Loops


Live Demo
var index = 10

repeat {
   print( "Value of index is \(index)")
   index = index + 1
while index < 20

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

Value of index is 10
Value of index is 11
Value of index is 12
Value of index is 13
Value of index is 14
Value of index is 15
Value of index is 16
Value of index is 17
Value of index is 18
Value of index is 19