Kotlin for loop

Last Updated : 20 May, 2019

In Kotlin, for loop is equivalent to foreach loop of other languages like C#. Here for loop is used to traverse through any data structure which provides an iterator. It is used very differently then the for loop of other programming languages like Java or C. The syntax of for loop in Kotlin:

  for(item in collection) {         // code to execute  }

In Kotlin, for loop is used to iterate through the following because all of them provides iterator.

Range
Array
String
Collection

Iterate through range using for loop -

You can traverse through Range because it provides iterator. There are many ways you can iterate through Range. The in operator used in for loop to check value lies within the Range or not. Below programs are example of traversing the range in different ways and in is the operator to check the value in the range. If value lies in between range then it returns true and prints the value.

Iterate through range to print the values:

Java

fun main(args: Array<String>) { for (i in 1..6) { print("$i ") } }

Output:

1 2 3 4 5 6

Iterate through range to jump using step-3 :

Java

fun main(args: Array<String>) { for (i in 1..10 step 3) { print("$i ") } }

Output:

1 4 7 10

You can not iterate through Range from top to down without using DownTo :

Java

fun main(args: Array<String>) { for (i in 5..1) { print("$i ") } println("It prints nothing") }

Output:

It prints nothing

Iterate through Range from top to down with using downTo :

Java

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

Output:

5 4 3 2 1

Iterate through Range from top to down with using downTo and step 3:

Java

fun main(args: Array<String>) { for (i in 10 downTo 1 step 3) { print("$i ") } }

Output:

10 7 4 1

Iterate through array using for loop -

Without using Index property
With Using Index property
Using withIndex Library Function

Traverse an array without using index property:

Java

fun main(args: Array<String>) {     var numbers = arrayOf(1,2,3,4,5,6,7,8,9,10)      for (num in numbers){         if(num%2 == 0){             print("$num ")         }     } }

Output:

2 4 6 8 10

Traverse an array with using index property:

Java

fun main(args: Array<String>) {      var planets = arrayOf("Earth", "Mars", "Venus", "Jupiter", "Saturn")      for (i in planets.indices) {         println(planets[i])     } }

Output:

  Earth  Mars  Venus  Jupiter  Saturn

Traverse an array using withIndex() Library Function:

Java

fun main(args: Array<String>) {     var planets = arrayOf("Earth", "Mars", "Venus", "Jupiter", "Saturn")      for ((index,value) in planets.withIndex()) {         println("Element at $index th index is $value")     } }

Output:

  Element at 0 th index is Earth  Element at 1 th index is Mars  Element at 2 th index is Venus  Element at 3 th index is Jupiter  Element at 4 th index is Saturn

Iterate through string using for loop -

Without using Index property
With Using Index property
Using withIndex Library Function

Java

fun main(args: Array<String>) {     var name = "Geeks"     var name2 = "forGeeks"          // traversing string without using index property     for (alphabet in name)   print("$alphabet ")      // traversing string with using index property     for (i in name2.indices) print(name2[i]+" ")     println(" ")          // traversing string using withIndex() library function     for ((index,value) in name.withIndex())     println("Element at $index th index is $value") }

Output:

  G e e k s f o r G e e k s    Element at 0 th index is G  Element at 1 th index is e  Element at 2 th index is e  Element at 3 th index is k  Element at 4 th index is s

Iterate through collection using for loop -

You can traverse the collection using the for loop. There are three types of collections list, map and set. In the listOf() function we can pass the different data types at the same time. Below is the program to traverse the list using for loop.

Java

fun main(args: Array<String>) {      // read only, fix-size     var collection = listOf(1,2,3,"listOf", "mapOf", "setOf")      for (element in collection) {         println(element)     } }

Output:

  1  2  3  listOf  mapOf  setOf

Kotlin when expression

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