For Loop
Visit every item in an array, one by one.
1fun main() {
2 val greetingWords = arrayOf("hello", "world", "!")
3 for (word in greetingWords) {
4 println(word)
5 }
6}
$ kotlinc Main.kt -include-runtime -d Main.jar
$ java -jar Main.jar
hello
world
!
Every line, explained
fun main() {- Every Kotlin program starts at the main function. When you run the program, Kotlin looks for fun main() and runs everything between its { and } from top to bottom.
val greetingWords = arrayOf("hello", "world", "!")- An array of text values; the items go inside arrayOf(...), each in its own double quotes.
for (word in greetingWords) {- for (item in items) visits each item in turn, one trip around the loop per item, and each time item holds the current value. No counter and no i++: in Kotlin a for loop walks over the items directly. Naming the loop variable word (singular) and the array greetingWords makes it read almost like English.
println(word)- println(...) prints whatever is inside the round brackets to the terminal, then moves to a new line. All lowercase, and no semicolon at the end; Kotlin does not need them. Runs three times, once per item, and word is different each time.
}- This } closes the for loop. Everything between the loop's { and } is repeated on every trip around the loop.
}- This closing curly brace } ends the main function. In Kotlin every opening brace { must have a matching closing brace }.