For Range Loop in Go

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February 15, 2025
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4 min read

The for range loop in Go is a powerful construct used to iterate over elements in arrays, slices, maps, channels, and strings. It simplifies looping by automatically handling indexing and retrieving values.

1. Syntax of for range Loop

Go
for key, value := range collection {
    // Code to execute
}

🔹 Key Points:
✅ key: Represents the index (for slices/arrays) or key (for maps).
✅ value: The actual value at the index or key.
✅ If the key is not needed, use _.

2. Using for range with Slices/Arrays

Go
package main

import "fmt"

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

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

🔹 Output:

Bash
Index: 0, Value: 10
Index: 1, Value: 20
Index: 2, Value: 30
Index: 3, Value: 40
Index: 4, Value: 50

👉 Explanation:

  • The index represents the position in the slice.
  • The value represents the actual element at that position.

3. Ignoring the Index

If the index is not needed, use _ to ignore it.

Go
for _, value := range nums {
    fmt.Println(value)
}

🔹 Output:

Bash
10
20
30
40
50

4. Using for range with Maps

In maps, for range iterates over keys and values.

Go
package main

import "fmt"

func main() {
    studentScores := map[string]int{"Alice": 85, "Bob": 90, "Charlie": 78}

    for name, score := range studentScores {
        fmt.Printf("Name: %s, Score: %d\n", name, score)
    }
}

🔹 Output:

Bash
Name: Alice, Score: 85
Name: Bob, Score: 90
Name: Charlie, Score: 78

👉 Explanation:

  • The name represents the key in the map.
  • The score represents the value associated with the key.

✅ Ignoring values and only iterating over keys:

Go
for name := range studentScores {
    fmt.Println("Student:", name)
}

5. Using for range with Strings

The for range loop can iterate over Unicode characters in a string.

Go
package main

import "fmt"

func main() {
    text := "Hello"

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

🔹 Output:

Bash
Index: 0, Character: H
Index: 1, Character: e
Index: 2, Character: l
Index: 3, Character: l
Index: 4, Character: o

👉 Explanation:

  • The index is the position of the character in the string.
  • The char is the actual Unicode character.

✅ Ignoring the index and printing only characters:

Go
for _, char := range text {
    fmt.Println(string(char))
}

6. Using for range with Channels

A for range loop can be used to receive values from a channel until it is closed.

Go
package main

import "fmt"

func main() {
    ch := make(chan int, 3)
    ch <- 1
    ch <- 2
    ch <- 3
    close(ch) // Closing the channel

    for value := range ch {
        fmt.Println(value)
    }
}

🔹 Output:

Bash
1
2
3

👉 Explanation:

  • The loop reads values from ch until it is closed.

7. Using for range with Structs (Custom Data Types)

You can also iterate over struct slices using for range.

Go
package main

import "fmt"

type Employee struct {
    Name  string
    Salary int
}

func main() {
    employees := []Employee{
        {"Alice", 5000},
        {"Bob", 6000},
        {"Charlie", 7000},
    }

    for _, emp := range employees {
        fmt.Printf("Name: %s, Salary: %d\n", emp.Name, emp.Salary)
    }
}

🔹 Output:

Bash
Name: Alice, Salary: 5000
Name: Bob, Salary: 6000
Name: Charlie, Salary: 7000

👉 Explanation:

  • The loop iterates over the slice of Employee structs and prints their details.

Conclusion

Data StructureIteration TypeExample
Slice/ArrayIndex & Valuefor i, v := range slice {}
MapKey & Valuefor k, v := range map {}
StringIndex & Characterfor i, ch := range "Hello" {}
ChannelValues from Channelfor v := range ch {}

🚀 Go’s for range loop is a powerful way to iterate over different data structures with clean and readable syntax.

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Go
nums := []int{10, 20, 30}
for index, value := range nums {
    fmt.Println(index, value)
}

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Go
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}

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Go
students := map[string]int{"Alice": 85, "Bob": 90}
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    fmt.Println(name, score)
}

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Go
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}

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Go
text := "Hello"
for _, char := range text {
    fmt.Println(string(char))
}

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Go
ch := make(chan int, 3)
ch <- 1
ch <- 2
ch <- 3
close(ch)

for value := range ch {
    fmt.Println(value)
}

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Go
type Employee struct {
    Name  string
    Salary int
}

employees := []Employee{
    {"Alice", 5000},
    {"Bob", 6000},
}

for _, emp := range employees {
    fmt.Println(emp.Name, emp.Salary)
}

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