for

// Three-part form (init; condition; post)
for i := 0; i < 10; i++ {
}

// Condition only (equivalent to while)
for condition {
}

// Infinite loop
for {
}

// Range-based iteration
for i, v := range slice {
}
for k, v := range mapVar {
}
for i, r := range str { // i = byte position, r = rune value
}

// Index or value only
for i := range slice {  // index only
}
for _, v := range slice { // value only (discard index with _)
}

package main

import "fmt"

func main() {
	// Three-part form
	sum := 0
	for i := 1; i <= 5; i++ {
		sum += i
	}
	fmt.Println("Sum:", sum) // 15

	// Iterate over a slice with range
	fruits := []string{"apple", "orange", "grape"}
	for i, v := range fruits {
		fmt.Printf("%d: %s\n", i, v)
	}

	// Iterate over a map with range
	scores := map[string]int{"Alice": 85, "Bob": 92}
	for name, score := range scores {
		fmt.Printf("%s: %d\n", name, score)
	}

	// Skip with continue (print even numbers only)
	for i := 0; i < 10; i++ {
		if i%2 != 0 {
			continue
		}
		fmt.Print(i, " ")
	}
	fmt.Println()

	// Use a labeled break to exit an outer loop all at once
outer:
	for i := 0; i < 3; i++ {
		for j := 0; j < 3; j++ {
			if i == 1 && j == 1 {
				break outer
			}
			fmt.Printf("(%d,%d) ", i, j)
		}
	}
	fmt.Println()
}

Range-based loops work with slices, arrays, maps, strings, and channels. When used on a string, range yields byte positions and rune values as pairs, so multi-byte characters such as CJK text are handled correctly one character at a time.

Values returned by range are copies. You cannot modify slice elements directly through a range loop. To modify elements, access them by index: for i := range s { s[i] = ... }.

Labeled break and continue use the same mechanism as labels. They are useful for breaking out of deeply nested loops at once, but overuse can make code harder to read.