How to Use repeat Function in Kotlin: Simple Guide

In Kotlin, you use the repeat function to run a block of code a specific number of times. It takes an integer for how many times to repeat and a lambda with the code to execute each time.

Syntax

The repeat function syntax is simple:

• repeat(times: Int) { /* code */ }
• times is how many times the code block runs.
• The code block inside { } runs each time.

kotlin

repeat(3) {
    println("Hello")
}

Output

Hello
Hello
Hello

Example

This example prints numbers from 0 to 4 using repeat. The lambda receives the current iteration index.

kotlin

fun main() {
    repeat(5) { index ->
        println("Number: $index")
    }
}

Output

Number: 0
Number: 1
Number: 2
Number: 3
Number: 4

Common Pitfalls

One common mistake is forgetting that the lambda parameter is zero-based index, so it starts at 0, not 1. Another is using repeat with a negative number, which throws an exception.

Also, avoid using repeat for side effects without clear intent, as it can reduce code readability.

kotlin

fun main() {
    // Correct: starting index at 1 by adding 1
    repeat(3) { index ->
        println("Count: ${index + 1}") // Correct way to start from 1
    }

    // Wrong: negative times causes error
    // repeat(-1) { println("Won't run") } // Throws IllegalArgumentException
}

Output

Count: 1
Count: 2
Count: 3

Quick Reference

Usage	Description
repeat(times) { code }	Runs code block times times.
repeat(times) { index -> code }	Runs code with zero-based index each time.
times must be >= 0	Negative values cause an exception.
Lambda parameter is optional	You can omit index if not needed.

Key Takeaways

Use repeat(times) { } to run code multiple times easily.

The lambda parameter is the zero-based index of the current iteration.

Passing a negative number to repeat causes an error.

You can omit the lambda parameter if you don't need the index.

Avoid using repeat for unclear side effects to keep code readable.