Kotlin supports the usual duo of loop constructs found in most languages - the while loop and the for loop. The syntax for while loops in Kotlin will be familiar to most developers, as it is exactly the same as most C-style languages:

 while (true) { println("This will print out for a long time!") } 

The Kotlin for loop is used to iterate over any object that defines a function or extension function with the name iterator. All collections provide this function:

 val list = listOf(1, 2, 3, 4) for (k in list) { println(k) } val set = setOf(1, 2, 3, 4) for (k in set) { println(k) } 

Note the syntax using the keyword in. The in operator is always used with for loops. In addition to collections, integral ranges are directly supported either inline or defined outside:

 val oneToTen = 1..10 for (k in oneToTen) { for (j in 1..5) { println...