Go – For Loop Range

The range keyword is used with the for loop to iterate over elements of arrays, slices, maps, strings, or channels. It simplifies iteration by providing both the index and the value of elements.

In this tutorial, we will cover its syntax and usage with practical examples.

Syntax of For Loop with Range

The syntax of the for loop with range is:

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for index, value := range collection {
    // Code to execute for each element
}

Here:

  • index: The index of the current element.
  • value: The value of the current element.
  • collection: The array, slice, map, string, or channel being iterated.

Example 1: Iterating Over a Slice

Let’s iterate over a slice of integers:

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package main

import "fmt"

func main() {
    numbers := []int{10, 20, 30, 40, 50}

    for index, value := range numbers {
        fmt.Printf("Index: %d, Value: %d\n", index, value)
    }
}

Output

Example 2: Iterating Over a Map

When iterating over a map, the range keyword returns the key and the value:

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package main

import "fmt"

func main() {
    countries := map[string]string{
        "US": "United States",
        "IN": "India",
        "JP": "Japan",
    }

    for key, value := range countries {
        fmt.Printf("Key: %s, Value: %s\n", key, value)
    }
}

Output

Example 3: Iterating Over a String

When iterating over a string, the range keyword returns the index and the Unicode code point of each character:

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package main

import "fmt"

func main() {
    text := "Golang"

    for index, char := range text {
        fmt.Printf("Index: %d, Character: %c\n", index, char)
    }
}

Output

Example 4: Ignoring Index or Value

If you don’t need the index or value, you can use the underscore (_) to ignore it:

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package main

import "fmt"

func main() {
    numbers := []int{10, 20, 30, 40, 50}

    // Ignore the index
    for _, value := range numbers {
        fmt.Println("Value:", value)
    }

    // Ignore the value
    for index := range numbers {
        fmt.Println("Index:", index)
    }
}

Output

When to Use For Loop Range

  • To iterate over arrays or slices for both index and value.
  • To traverse maps for keys and values.
  • To loop through characters in a string by index and Unicode code points.
  • To work with channels for receiving values.

Conclusion

The for loop with range in Go provides a concise and efficient way to iterate over collections such as arrays, slices, maps, and strings. Its versatility and simplicity make it a powerful tool for looping through various data structures.