How to make reversed for loop with array index as a start/end point in Kotlin?

Question

now i'm trying to make reversed for a loop.The simple way of reverse for is for(i in start downTo end)

but,what if I use array as a start/end point?

Answer 1

You can loop from the last index calculated by taking size - 1 to 0 like so:

for (i in array.size - 1 downTo 0) {
    println(array[i])
}

Even simpler, using the lastIndex extension property:

for (i in array.lastIndex downTo 0) {
    println(array[i])
}

Or you could take the indices range and reverse it:

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

Answer 2

Additionally to the first answer from zsmb13, some other variants.

Using IntProgression.reversed:

for (i in (0..array.lastIndex).reversed())
    println("On index $i the value is ${array[i]}")

or using withIndex() together with reversed()

array.withIndex()
        .reversed()
        .forEach{ println("On index ${it.index} the value is ${it.value}")}

or the same using a for loop:

for (elem in array.withIndex().reversed())
    println("On index ${elem.index} the value is ${elem.value}")

or if the index is not needed

for (value in array.reversed())
    println(value)