3.9. Kotlin cycle control

3.9.1. For cycle #

for loop can provide an iterator for any iterator syntax isas follows:

for (item in collection) print(item) 

The body of the loop can be a code block:

for (item: Int in ints) { // …… } 

As mentioned above for you can loop through any object that provides aniterator.

If you want to traverse an array or an list you can do this:

for (i in array.indices) { print(array[i]) } 

Note that this “traversal on the interval” is compiled into an optimized implementation without creating additional objects.

Or you can use library functions withIndex :

for ((index, value) in array.withIndex()) { println("the element at $index is $value") } 

fun main(args: Array<String>) { val items = listOf("apple", "banana", "kiwi") for (item in items) { println(item) } for (index in items.indices) { println("item at $index is ${items[index]}") } } 

apple banana kiwi item at 0 is apple item at 1 is banana item at 2 is kiwi 

3.9.2. While and do…while cycle #

while is the most basic loop, and its structure is:

While (Boolean expression) { //Circular Content } 

do…while loop for while statement, you cannot enter a loop if the condition is not met. But sometimes we need to execute at least once, even if the conditions are not met.

do…while cyclic and while cycle is similar, except that do…while loop is executed at least once.

do { //code statement }While (Boolean expression); 

fun main(args: Array<String>) { println("----while use-----") var x = 5 while (x > 0) { println( x--) } println("----do...while use-----") var y = 5 do { println(y--) } while(y>0) }