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)