Repeat while a condition holds

Some repetition depends on a condition rather than a known list. A while loop checks its condition before each body execution. A repeat-while loop checks after the body, so it runs at least once. This distinction matters for retries and input prompts.

The loop must make progress toward stopping, or it may run indefinitely. Track which value changes and when the condition observes that change. A condition false initially skips a while body but not a repeat-while body.

Save this complete program as main.swift and run it with the Swift toolchain. No separate input file is needed.

Swift · complete program

var remaining = 3
while remaining > 0 {
  print(remaining)
  remaining -= 1
}
print("Ready")

Expected output

3
2
1
Ready

Follow the execution

The program prints 3, 2 and 1 while subtracting one after each display. The next condition sees zero and ends the loop. Ready then prints once. Omitting the subtraction would leave the condition true indefinitely.

Try this program in the Swift compiler. Paste the complete source above.

Your task: What happens if remaining starts at zero?

Swift · complete program

var remaining = 3
while remaining > 0 {
  print(remaining)
  remaining -= 1
}
print("Ready")

Worked answer

The while body runs zero times, and Ready prints immediately. A repeat-while version would run its body once before discovering the false condition.

Retries need limits and appropriate failure handling. Repeatedly checking a resource without waiting or an event mechanism can waste CPU time; this small counter is a teaching loop rather than a production polling design.

The while body runs zero times, and Ready prints immediately. A repeat-while version would run its body once before discovering the false condition. Retries need limits and appropriate failure handling.

Further reading: official Swift language guide.