Kotlin for Loop

Kotlin for loop is used to iterate a part of program several times. It iterates through arrays, ranges, collections, or anything that provides for iterate. Kotlin for loop is equivalent to the foreach loop in languages like C#.

for (item in collection){  
//body of loop  
}  
for (item in collection){  
//body of loop  
}  

Iterate through array

Let's see a simple example of iterating the elements of array.

fun main(args : Array< String>) {  
    val marks = arrayOf(80,85,60,90,70)  
    for(item in marks){  
        println(item)  
    }  
}  
fun main(args : Array< String>) {  
    val marks = arrayOf(80,85,60,90,70)  
    for(item in marks){  
        println(item)  
    }  
} 

80
85
60
90
70

If the body of for loop contains only one single line of statement, it is not necessary to enclose within curly braces {}.

fun main(args : Array< String>) {  
    val marks = arrayOf(80,85,60,90,70)  
    for(item in marks)  
        println(item)  
}  
fun main(args : Array< String>) {  
    val marks = arrayOf(80,85,60,90,70)  
    for(item in marks)  
        println(item)  
} 

The elements of an array are iterated on the basis of indices (index) of array. For example:

fun main(args : Array< String>) {  
     
    val marks = arrayOf(80,85,60,90,70)  
    for(item in marks.indices)  
       println("marks[$item]: "+ marks[item])  
}  
fun main(args : Array< String>) {  
     
    val marks = arrayOf(80,85,60,90,70)  
    for(item in marks.indices)  
       println("marks[$item]: "+ marks[item])  
}   

marks[0]: 80
marks[1]: 85
marks[2]: 60
marks[3]: 90
marks[4]: 70

Iterate through range

Let's see an example of iterating the elements of range.

fun main(args : Array< String>) {  
  
    print("for (i in 1..5) print(i) = ")  
    for (i in 1..5) print(i)  
    println()  
    print("for (i in 5..1) print(i) = ")  
    for (i in 5..1) print(i)             // prints nothing  
    println()  
    print("for (i in 5 downTo 1) print(i) = ")  
    for (i in 5 downTo 1) print(i)  
    println()  
    print("for (i in 5 downTo 2) print(i) = ")  
    for (i in 5 downTo 2) print(i)  
    println()  
    print("for (i in 1..5 step 2) print(i) = ")  
    for (i in 1..5 step 2) print(i)  
    println()  
    print("for (i in 5 downTo 1 step 2) print(i) = ")  
    for (i in 5 downTo 1 step 2) print(i)  
}  
fun main(args : Array< String>) {  
  
    print("for (i in 1..5) print(i) = ")  
    for (i in 1..5) print(i)  
    println()  
    print("for (i in 5..1) print(i) = ")  
    for (i in 5..1) print(i)             // prints nothing  
    println()  
    print("for (i in 5 downTo 1) print(i) = ")  
    for (i in 5 downTo 1) print(i)  
    println()  
    print("for (i in 5 downTo 2) print(i) = ")  
    for (i in 5 downTo 2) print(i)  
    println()  
    print("for (i in 1..5 step 2) print(i) = ")  
    for (i in 1..5 step 2) print(i)  
    println()  
    print("for (i in 5 downTo 1 step 2) print(i) = ")  
    for (i in 5 downTo 1 step 2) print(i)  
}  

for (i in 1..5) print(i) = 12345
for (i in 5..1) print(i) = 
for (i in 5 downTo 1) print(i) = 54321
for (i in 5 downTo 2) print(i) = 5432
for (i in 1..5 step 2) print(i) = 135
for (i in 5 downTo 1 step 2) print(i) = 531