Justin Joyce

Practical tips and tutorials about software development.

Golang for loop

Go has a few for loop options:

  1. Classic for: for i := 0; i < 5; i++
  2. for using range: for index, element := range listOfThings
  3. for as a while loop: for done != true

Classic for loop

This format is common in many languages:

func main() {
	for i := 0; i < 3; i++ {
    	fmt.Printf("Hi %d\n", i)
    }
}

main()
// Hi 0
// Hi 1
// Hi 2

The one difference in Go is the lack of opening parentheses around the init statements1, which are required in other languages like Javascript, Java, or C.

For loop using range

Golang doesn’t have a for in loop, but range acts similarly:

func main() {
	letterSlice := []string{"a", "b", "c"}
	for index, letter := range letterSlice {
		fmt.Printf("Index: %d, Letter: %s\n", index, letter)
	}
}

main()
// Index: 0, Letter: a
// Index: 1, Letter: b
// Index: 2, Letter: c

For loop as a while loop

Many languages have a for loop and a separate while loop—Go does not.

For is Go’s while:

func main() {
	complete := false
    for != complete {
    	// this will loop until you set complete = true inside the loop
    }
}

Break and continue statements

These work as expected with any of Go’s loop formats.

Continue skips to the next loop iteration:

func main() {
	for i := 0; i < 3; i++ {
    	if i == 1 {
        	fmt.Println("i == 1, skipping")
        	continue
        }
    	fmt.Printf("Hi %d\n", i)
    }
}

main()
// Hi 0
// i == 1, skipping
// Hi 2

Break exits the loop:

func main() {
	letterSlice := []string{"a", "b", "c"}
	for index, letter := range letterSlice {
		if letter == "c" {
        	fmt.Printf("found c, exiting loop")
			break
		}
		fmt.Printf("Index: %d, Letter: %s\n", index, letter)
	}
}

main()
// Index: 0, Letter: a
// Index: 1, Letter: b
// found c, exiting loop

If you have nested loops break and continue will only affect the innermost loop, but that’s common across all languages, not just Go.

  1. Technically it’s the init, condition, and post statements ↩︎