Kotlin do-while Loop

In this tutorial, we will cover the do-while loop in Kotlin. The do-while loop is just like the Kotlin while loop with just one difference, that no matter what condition you provide in the do-while loop, the loop will execute once because the condition is checked after the loop code has been executed.

Here is the basic syntax for the do-while loop:

do {
    // Block of code to be executed
}while (condition)

The working of do-while loop is as follows:

• For the first time, the statements written in do block is executed without checking the condition.
• After executing the do block, the condition specified in while is checked.
• If the condition is true, again do block is executed. Else, execution of the loop ends.

Let us take an example to print all the even numbers from 1 to 10:

fun main() {
    var number = 1
    do {
        if(number % 2 == 0)
            println(number)
        number++
    }while (number <= 10)
}

Output:

2 

4 

6 

8 

10

Try running the above code to print even numbers from 1 to 100, all you have to do is modify the condition for the do-while loop.

Like we mentioned in the introduction, the do-while loop will execute at least once, even if the condition is always false. Let us see this with an example:

fun main() {
    do {
        println("Hello World!!")
    }while (false)
}

Output:

Hello World!!

In the above code example, we can see that the output is printed once even if the condition is always false.

There is a slight difference between while loop and do-while loop:

• while loop is entry controlled loop and do-while loop is exit controlled loop.
• At minimum, do-while loop will execute atleast one time but while loop may not execute even a single time if the condition is false.

In this tutorial we covered the Kotlin do-while loop, with code examples and we also saw how it is different from Kotlin while loop. In the next tutorial we will cover the Kotlin for loop.