Kotlin While and Do While

How it works

while checks its condition before the body; do-while checks afterward and runs at least once. Each loop needs progress toward termination. These forms suit state-based repetition better than a for loop when the number of iterations is not known up front.

Run this Kotlin example

These are local Kotlin/JVM programs. Install a JDK and the compiler using the official Kotlin compiler guide, or use an IDE with Kotlin support. Check java -version and kotlinc -version in a new terminal. The reviewed compiler is Kotlin 2.4.21 with a JVM 21 target, executed on Temurin JDK 25.0.5. Use JDK 21 or newer for this target. Android, Kotlin/JS and Kotlin/Native require separate platform projects and are not the tested environment here.

Save the complete source as while-do-while.kt in its own learning folder. The package line gives this example a namespace, not a network address. Bhylu has no Kotlin browser runner; do not use the JavaScript or Python editor. Apache, PHP and MySQL are not required.

Compile with kotlinc while-do-while.kt -jvm-target 21 -include-runtime -d lesson.jar, then run java -jar lesson.jar. Use a learning folder you own and keep generated JARs outside the website. These sources require no third-party application libraries.

Download the complete while-do-while.kt · Download all source files with hash checks

For the optional collection, save download-examples.mjs in a new learning folder and run node download-examples.mjs. A local preview uses node download-examples.mjs http://127.0.0.1:8000/examples/kotlin/. It refuses an existing bhylu-kotlin-examples folder and installs or executes no Kotlin code. Compile one ordinary lesson at a time by filename.

Example

package bhylu.lessons.k_while_do_while

fun main() {
    var remaining = 3
    while (remaining > 0) {
        println(remaining)
        remaining--
    }
    var checks = 0
    do { checks++ } while (checks < 1)
    println("checks=$checks")
}

Expected result

3
2
1
checks=1

remaining decreases every time, so the first loop reaches zero. The second loop demonstrates the guaranteed first pass without inventing input to make it run.