How to Use For Range Loop in Go: Simple Guide

In Go, use the for range loop to iterate over elements in arrays, slices, maps, or strings. It returns the index (or key) and value for each item, making it easy to process collections.

Syntax

The for range loop has this basic form:

for index, value := range collection {
    // use index and value
}

Here, collection can be an array, slice, map, or string. index is the position or key, and value is the element at that position.

You can omit index or value by using an underscore _ if you don't need them.

go

for index, value := range collection {
    // code using index and value
}

Example

This example shows how to use for range to loop over a slice of fruits and print each index and fruit name.

go

package main

import "fmt"

func main() {
    fruits := []string{"apple", "banana", "cherry"}
    for i, fruit := range fruits {
        fmt.Printf("Index: %d, Fruit: %s\n", i, fruit)
    }
}

Output

Index: 0, Fruit: apple
Index: 1, Fruit: banana
Index: 2, Fruit: cherry

Common Pitfalls

• Forgetting to use the underscore _ when you want to ignore the index or value causes unused variable errors.
• Modifying the loop variable inside the loop does not change the original collection.
• When ranging over a map, the order of iteration is random, so do not rely on order.

go

package main

import "fmt"

func main() {
    nums := []int{10, 20, 30}

    // Wrong: unused index causes error
    // for i, num := range nums {
    //     fmt.Println(num)
    // }

    // Correct: ignore index with _
    for _, num := range nums {
        fmt.Println(num)
    }
}

Output

10
20
30

Quick Reference

Use this quick guide when working with for range loops:

• Arrays/Slices: for i, v := range slice
• Maps: for key, val := range map
• Strings: for i, ch := range str (ch is a rune)
• Use _ to ignore index or value if not needed
• Map iteration order is random

Key Takeaways

Use for range to loop over arrays, slices, maps, and strings easily.

The loop returns index (or key) and value for each element.

Use underscore _ to ignore unwanted values and avoid errors.

Map iteration order is random; do not rely on it.

Modifying loop variables does not change the original collection.