Kotlin: while, do-while loops

while loop

while statement executes a block of statements until a particular condition is true

Syntax

while (expression) {

      //statements

}

The expression in the while statement must evaluates to a boolean value, otherwise compiler will throw error. While statement first evaluates the expression, until the expression evaluates to true, it executes the code inside the while block, otherwise it comes out of the while loop.

Example: Print numbers from 0 to 9 using while loop.

WhileDemo.kt

fun main(args: Array<String>) {

 var counter : Int = 0
 
 while(counter < 10){
  println(counter)
  counter++
 }
}

Output

0
1
2
3
4
5
6
7
8
9

do-while loop

do-while is also a loop construct like while, but evaluates its expression at the bottom of the loop instead of the top.

    Syntax

    do {

        //statement(s)

    } while (expression)

DoWhileDemo.kt

fun main(args: Array<String>) {

 var counter : Int = 0
 
 do{
  println(counter)
  counter++
 }while(counter < 10)
}

Output

0
1
2
3
4
5
6
7
8
9

What is the difference between while and do-while ?
Statements within the do block are always execute at least once even if the expression evaluates to false.

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