Kotlin in Hindi while loop

Loop is used in programming to repeat a specific block of code. In this article, you will learn to create while and do...while loops in Kotlin programming.

Kotlin while Loop

The syntax of while loop is:

while (testExpression) {
    // codes inside body of while loop
}

How while loop works?

The test expression inside the parenthesis is a Boolean expression.

If the test expression is evaluated to true,

  • statements inside the while loop are executed.
  • then, the test expression is evaluated again.

This process goes on until the test expression is evaluated to false.

If the test expression is evaluated to false,

  • while loop is terminated.

Example: Kotlin while Loop

// Program to print line 5 times

fun main(args: Array<String>) {

    var i = 1

    while (i <= 5) {
        println("Line $i")
        ++i
    }
}

When you run the program, the output will be:

Line 1
Line 2
Line 3
Line 4
Line 5

Notice, ++i statement inside the while loop. After 5 iterations, variable i will be incremented to 6. Then, the test expression i <= 5 is evaluated to false and the loop terminates.


If the body of loop has only one statement, it's not necessary to use curly braces { }.


Example: Compute sum of Natural Numbers

// Program to compute the sum of natural numbers from 1 to 100.
fun main(args: Array<String>) {

    var sum = 0
    var i = 100

    while (i != 0) {
        sum += i     // sum = sum + i;
        --i
    }
    println("sum = $sum")
}

When you run the program, the output will be:

sum = 5050

Here, the variable sum is initialized to 0 and i is initialized to 100. In each iteration of while loop, variable sum is assigned sum + i, and the value of i is decreased by 1 until i is equal to 0. For better visualization,

1st iteration: sum = 0+100 = 100, i = 99
2nd iteration: sum = 100+99 = 199, i = 98
3rd iteration: sum = 199+98 = 297, i = 97
... .. ...
... .. ...
99th iteration: sum = 5047+2 = 5049, i = 1
100th iteration: sum = 5049+1 = 5050, i = 0 (then loop terminates)