The range Keyword

Ranging Over a Slice

range on a slice or array gives you both the index and the value at each step, letting you avoid manually managing an index variable and bounds checks.

Example: Ranging Over a Slice

package main

import "fmt"

func main() {
	fruits := []string{"apple", "banana", "cherry"}
	for i, fruit := range fruits {
		fmt.Println(i, fruit)
	}
}

Ignoring the Index or Value

If you only care about the value and not the index (or vice versa), the blank identifier _ discards the part you don't need, satisfying Go's rule that every declared variable must be used.

Note: Go's compiler rejects a declared-but-unused variable, so _ is essential when you only need one of the two range values.

Example: Ignoring the Index or Value

package main

import "fmt"

func main() {
	fruits := []string{"apple", "banana", "cherry"}
	for _, fruit := range fruits {
		fmt.Println("fruit:", fruit)
	}
}

Ranging Over a Map

range on a map yields each key-value pair, but the order of iteration is deliberately randomized by the Go runtime every time the program runs, which prevents code from accidentally depending on a specific order.

Note: Map iteration order is intentionally randomized by Go each run -- never rely on it being consistent.

Example: Ranging Over a Map

package main

import "fmt"

func main() {
	ages := map[string]int{"Amit": 30, "Sara": 25}
	total := 0
	for _, age := range ages {
		total += age
	}
	fmt.Println("total age:", total)
}

Ranging Over a String

range on a string decodes it as UTF-8, yielding the byte index and the rune (full character) at that position -- correctly handling multi-byte characters, unlike a plain byte-index loop.

Example: Ranging Over a String

package main

import "fmt"

func main() {
	for i, r := range "Go!" {
		fmt.Printf("%d: %c\n", i, r)
	}
}