go by example for loop with range
In Go, range is used to iterate over data types and return corresponding values: 1. For slices and arrays, range returns indexes and element copies; 2. Unwanted indexes or values can be ignored using _; 3. For maps, range returns keys and values, but the iteration order is not fixed; 4. For strings, range returns rune indexes and characters (rune type), supporting Unicode; 5. For channels, range continues to read values until the channel is closed, and only a single element is returned. Using range can avoid manually managing indexes, making iteratives simpler and safer.
In Go, the for loop combined with the range keyword is commonly used to iterate over arrays, slices, strings, maps, and channels. Here's a clear example for each major use case.
1. Looping over a slice with range
package main
import "fmt"
func main() {
fruits := []string{"apple", "banana", "cherry"}
for index, value := range fruits {
fmt.Printf("Index: %d, Value: %s\n", index, value)
}
}Output:
Index: 0, Value: apple Index: 1, Value: banana Index: 2, Value: cherry
rangereturns two values: the index and a copy of the element at that index.
2. Ignoring the index or value
If you don't need the index:
for _, value := range fruits {
fmt.Println("Fruit:", value)
}If you only need the index:
for index := range fruits {
fmt.Println("Index:", index)
}Use
_to ignore values you don't need.
3. Looping over a map
ages := map[string]int{
"Alice": 25,
"Bob": 30,
"Charlie": 35,
}
for key, value := range ages {
fmt.Printf("Name: %s, Age: %d\n", key, value)
}Map iteration order is not guaranteed — it's randomized in Go.
4. Looping over a string
s := "Go"
for index, char := range s {
fmt.Printf("Index: %d, Character: %c\n", index, char)
}Output:
Index: 0, Character: G Index: 1, Character: o
Note:
charis arune(Unicode code point), not a byte, which matters for multi-byte characters like "Hello World".
5. Looping over an array
numbers := [3]int{10, 20, 30}
for i, v := range numbers {
fmt.Printf("Position %d: %d\n", i, v)
}Same behavior as slices.
Summary of range behaviors:
| Data Type | First value | Second value |
|---|---|---|
| Slice / Array | Index (int) | Element (copy) |
| String | Rune index (int) | Rune (rune type) |
| Map | Key | Value |
| Channel | N/A (only one value: element) | — |
For channels,
rangereads values until the channel is closed.
Example with channel:
ch := make(chan int, 2)
ch <- 1
ch <- 2
close(ch)
for value := range ch {
fmt.Println("Received:", value)
} Basically, range makes iteration clean and safe — no manual index management needed. Just remember to use _ when you don't need a value, and know what range returns for each type.
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