Ranges

There is a set of tools for defining ranges in Kotlin. Let's have a brief look at them.

fun main() {
    for(i in 0..3) {             // 1
        print(i)
    }
    print(" ")

    for(i in 0 until 3) {        // 2
        print(i)
    }
    print(" ")

    for(i in 2..8 step 2) {      // 3
        print(i)
    }
    print(" ")

    for (i in 3 downTo 0) {      // 4
        print(i)
    }
    print(" ")

}

1. Iterates over a range starting from 0 up to 3 (inclusive). Like 'for(i=0; i<=3; ++i)' in other programming languages (C/C++/Java).
2. Iterates over a range starting from 0 up to 3 (exclusive). Like for loop in Python or like 'for(i=0; i<3; ++i)' in other programming languages (C/C++/Java).
3. Iterates over a range with a custom increment step for consecutive elements.
4. Iterates over a range in reverse order.

Char ranges are also supported:

fun main() {
    for (c in 'a'..'d') {        // 1
        print(c)
    }
    print(" ")

    for (c in 'z' downTo 's' step 2) { // 2
        print(c)
    }
    print(" ")

}

1. Iterates over a char range in alphabetical order.
2. Char ranges support step and downTo as well.

Ranges are also useful in if statements:

fun main() {
    val x = 2
    if (x in 1..5) {            // 1
        print("x is in range from 1 to 5")
    }
    println()

    if (x !in 6..10) {          // 2
        print("x is not in range from 6 to 10")
    }
}

1. Checks if a value is in the range.
2. !in is the opposite of in.