Kotlin Loops

Kotlin Loops:
Loops are used in cases where you need to repeat a set of instructions over and over again until a certain condition is met.
There are three primary types of looping in Kotlin.

For Loop - Back to top

Example:

fun main(args: Array<String>) {
    for( i in 1..5)
    {
        print(i)
    }
}

Output:
12345

A for loop contains two operations. The first operation i is initializing the loop with iterable i.
The second operation is checking upto when the loop is valid. In this case, the loop is valid for i range 1 to 5.

While Loop - Back to top

Example:

fun main(args: Array<String>) {
    var i: Int = 0
    while(i < 10)
    {
        println(i)
        i++
    }
}

Output:
0
1
2
3
4
5
6
7
8
9

A While loop variable is initialized before the statement.
Here we initialized i to 0. In the while statement, we have kept until when the loop is valid.

So here we check up to i < 10. Inside the while loop we are printing i and then incrementing it by 1.
Imagine what would happen if we don't increment i by 1?
The loop will keep running a concept called infinite loop. Eventually the program will crash.

Do While Loop - Back to top

Example:

fun main(args: Array<String>) {
    var i: Int = 0
    do{
        println(i)
        i++;
    }while(i < 10)
}

Output:
0
1
2
3
4
5
6
7
8
9

A do.. While loop is similar to a while loop except one significant difference.
In do while loop you are guaranteed that the loop will execute at least once.
This is because the condition i < 10 is checked at the end of the execution.

Break and Continue:
Break statement:
A break statement will stop the current loop and it will continue to the next statement of the program after the loop.
Example of Break:

fun main(args: Array<String>) {
    var i: Int = 0
    while(i < 10)
    {
        i += 1;
        print(i)
        if(i == 5)
        {
            break
        }
    }
}

Output:
12345

In the above random example, we are incrementing i from an initial value of 0 by 1.
When the value of i is 5, we are breaking the loop.

Continue Statement:
Continue will stop the current iteration of the loop and it will start the next iteration.
It is very useful when we have some exception cases, but do not wish to stop the loop for such scenarios.

Example:

fun main(args: Array<String>) {
    var i: Int = 0
    while(i < 10)
    {
        i++
        if(i%2 == 0)
        {
            continue
        }
        print(i)
    }
}

Output:
13579

In the above example, we are skipping all even numbers via the if conditional check i%2.
So we end up printing only odd numbers.