While and do-while loops

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

While checks before its body. Do-while checks after its body and therefore runs at least once. Identify which state changes toward termination; a condition that stays true indefinitely creates an infinite loop even though the code compiles.

Save the complete source as Main.kt and use the Kotlin/JVM environment. No separate input file is needed.

Kotlin/JVM · complete program

fun main() {
  var remaining = 3
  while (remaining > 0) {
    println(remaining)
    remaining--
  }
  println("Ready")
}

Expected output

3
2
1
Ready

Follow the execution

The program prints three, two and one, decrementing after each display. At zero the next condition fails and Ready prints. No timer or asynchronous waiting is being simulated.

Try this in the Kotlin compiler by pasting the complete program.

Your task: What happens if remaining starts at zero?

Kotlin/JVM · complete program

fun main() {
  var remaining = 3
  while (remaining > 0) {
    println(remaining)
    remaining--
  }
  println("Ready")
}

Worked answer

The while body is skipped and Ready prints immediately. A do-while body would execute once before testing.

Retries need bounds and a failure policy. Repeated polling without waiting or an event mechanism can waste resources. This counter demonstrates control flow rather than a production waiting mechanism.

The while body is skipped and Ready prints immediately. A do-while body would execute once before testing. Retries need bounds and a failure policy.

Further reading: official Kotlin documentation for this topic.