Kotlin While Loop
A while loop repeats a block while its condition stays true. The condition is checked before each run of the block.
A counter ends the loop
The counter starts at 1 and grows on each run. The loop stops when the counter passes 3.
fun main() {
var count = 1
while (count <= 3) {
println(count)
count++
}
}A false condition runs zero times
The counter starts past the limit the condition allows. The line after the loop still prints and shows the counter unchanged.
fun main() {
var count = 5
while (count <= 3) {
println(count)
count++
}
println(count)
}do-while runs at least once
The condition is false from the start in this program. The counter still reaches 1 because the block runs before the check.
fun main() {
var runs = 0
do {
runs++
} while (runs < 0)
println(runs)
}A while loop builds a total
Each run adds the counter to a running total. The print after the loop shows the finished total.
fun main() {
var number = 1
var total = 0
while (number <= 4) {
total += number
number++
}
println(total)
}Example
fun main() {
var left = 3
while (left > 0) {
println(left)
left--
}
println(left)
}Key points
- while: a loop that repeats while a condition stays true.
- Use while with a condition and a block in braces.
- A counter changed inside the block can make the condition false.
- A while loop with a false first condition runs zero times.
- do-while: a loop that checks its condition after the block.
In this example, left starts at 3. The loop prints left and then lowers it by 1 on each run. The loop prints 3 and 2 and 1 in order. The condition fails when left reaches 0 and the loop ends. The last print shows 0.
Note
A condition that never becomes false makes the loop run without end.
Try it Yourself
Edit the code, then press Run.
Running is simulated · Kotlin Playground
Exercise
A do-while loop adds 1 to a counter that starts at 0. Its condition is counter < 0. What does the counter hold after the loop?