How to Use downTo in Kotlin for Descending Ranges

In Kotlin, downTo is used to create a descending range from a higher number down to a lower number. You can use it in loops like for (i in 10 downTo 1) to count backwards easily.

Syntax

The downTo function creates a range that goes from a higher value down to a lower value, including both ends.

Syntax parts:

• start downTo end: Creates a range from start down to end.
• The range includes both start and end.
• Commonly used in for loops to iterate backwards.

kotlin

val range = 10 downTo 1

Example

This example shows how to use downTo in a for loop to print numbers from 5 down to 1.

kotlin

fun main() {
    for (i in 5 downTo 1) {
        println(i)
    }
}

Output

5
4
3
2
1

Common Pitfalls

One common mistake is to expect downTo to work like .. (upwards range) without realizing it counts backwards. Also, using downTo with a start value less than the end value results in an empty range.

Wrong example: 1 downTo 5 produces no values.

Right way: Always ensure the start is greater than or equal to the end.

kotlin

fun main() {
    // Wrong: start less than end, no output
    for (i in 1 downTo 5) {
        println(i) // This will not print anything
    }

    // Correct: start greater than end
    for (i in 5 downTo 1) {
        println(i) // Prints 5 to 1
    }
}

Output

5
4
3
2
1

Quick Reference

Usage	Description
start downTo end	Creates a descending range from start to end, inclusive
for (i in x downTo y)	Iterates from x down to y in a loop
start downTo end step n	Iterates down with a step size n
start downTo end with start < end	Creates an empty range (no iteration)

Key Takeaways

Use downTo to create descending ranges from a higher to a lower number.

Always ensure the start value is greater than or equal to the end value to get a valid range.

You can use downTo in for loops to count backwards easily.

Adding step after downTo lets you skip numbers while counting down.

If start is less than end, downTo creates an empty range with no iterations.