Go Range Loop

The range keyword iterates over collections like arrays, slices, maps, and strings without manually managing index variables. It is the idiomatic Go way to loop over data structures.

Range Over a Slice

Range returns two values on each iteration: the index and the value at that index.

package main

import "fmt"

func main() {
    fruits := []string{"Apple", "Banana", "Mango"}

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

Output:

Index 0: Apple
Index 1: Banana
Index 2: Mango

Range Diagram

fruits := ["Apple", "Banana", "Mango"]
           ───┬───  ───┬────  ───┬───
              │         │         │
           index 0   index 1   index 2

for index, value := range fruits
         │          │
         │          └── the actual element at that position
         └───────────── the position number (0, 1, 2...)

Ignoring the Index

Use _ to discard the index when only the value is needed.

package main

import "fmt"

func main() {
    scores := []int{90, 85, 78, 92}

    for _, score := range scores {
        fmt.Println(score)
    }
}

Output:

90
85
78
92

Ignoring the Value

Use only the index when the value is not needed.

package main

import "fmt"

func main() {
    items := []string{"A", "B", "C"}

    for i := range items {
        fmt.Println("Position:", i)
    }
}

Range Over a Map

Range over a map returns each key-value pair. The order is not guaranteed in maps.

package main

import "fmt"

func main() {
    capitals := map[string]string{
        "India":  "New Delhi",
        "France": "Paris",
        "Japan":  "Tokyo",
    }

    for country, capital := range capitals {
        fmt.Printf("%s → %s\n", country, capital)
    }
}

Output (order may vary):

India → New Delhi
France → Paris
Japan → Tokyo

Range Over a String

Ranging over a string returns each character as a rune (Unicode code point) along with its byte index.

package main

import "fmt"

func main() {
    word := "Go!"

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

Output:

Index 0: G
Index 1: o
Index 2: !

Range Over an Integer (Go 1.22+)

Starting from Go 1.22, range can iterate directly over an integer number.

package main

import "fmt"

func main() {
    for i := range 5 {
        fmt.Println(i)
    }
}

Output:

0
1
2
3
4

Comparison: for vs range

Key Points

• range works on slices, arrays, maps, strings, and channels
• It returns index and value — use _ to ignore either one
• Ranging over a map does not guarantee order
• Ranging over a string gives Unicode runes, not raw bytes