Kotlin Tutorial · Kotlin Basics · Lesson 8 of 31

Kotlin Loops and Ranges

Loop with for over ranges and collections, while and do-while, and control loops with break and continue.

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for and ranges

for iterates over anything iterable. Ranges: 1..5 (inclusive), 1..<5 (excludes 5), 5 downTo 1, step 2. withIndex() gives the index and the value.

for loops and ranges

fun main() {
    for (i in 1..3) print("$i ")
    println()
    for (i in 0..<3) print("$i ")
    println()
    for (i in 10 downTo 0 step 5) print("$i ")
    println()
    val fruits = listOf("apple", "banana", "cherry")
    for ((index, fruit) in fruits.withIndex()) println("$index: $fruit")
}

Output

1 2 3 
0 1 2 
10 5 0 
0: apple
1: banana
2: cherry

Run this on your computer — see “Get Started” for setup.

while, break and continue

while and do { } while () work as in other languages. break and continue can target an outer loop with a label (outer@).

while, continue and labelled break

fun main() {
    var stock = 3
    while (stock > 0) {
        println("Selling one, $stock left before sale")
        stock--
    }

    outer@ for (row in 1..3) {
        for (col in 1..3) {
            if (col == 2) continue
            if (row == 3) break@outer
            print("($row,$col) ")
        }
    }
    println()
}

Output

Selling one, 3 left before sale
Selling one, 2 left before sale
Selling one, 1 left before sale
(1,1) (1,3) (2,1) (2,3)

Run this on your computer — see “Get Started” for setup.

Test yourself

Which range excludes its upper bound?

1..5
1..<5
5 downTo 1
1 until..5

Show answer

Answer: 1..<5

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