Loops (for)

Introduction

Most languages give you several looping keywords — for, while, do-while, foreach. Go simplifies this down to a single keyword, for, that flexibly covers every one of those styles. Once you understand its variations, you have everything you need to loop over anything in Go.

Why Go Has Only One Loop Keyword

True to its philosophy of "one way to do things," Go deliberately has no separate while or do-while keyword. The single for keyword adapts based on what you put in its header — a full three-part clause, a single condition, nothing at all, or a range clause — covering every loop style other languages need multiple keywords for.

The C-Style for Loop

The most familiar form has three parts separated by semicolons: an initialization statement, a condition, and a post statement — exactly like C, Java, or JavaScript.

package main

import "fmt"

func main() {
	for i := 0; i < 5; i++ {
		fmt.Println("Iteration:", i)
	}
}

The while-Style Loop

Drop the initialization and post statements, keeping only a condition, and for behaves exactly like a while loop in other languages.

package main

import "fmt"

func main() {
	count := 3

	for count > 0 {
		fmt.Println("Countdown:", count)
		count--
	}
	fmt.Println("Liftoff!")
}

The Infinite Loop

Omit the condition entirely and for loops forever, until something inside the loop body explicitly stops it with break or return.

package main

import "fmt"

func main() {
	n := 0

	for {
		if n == 3 {
			break
		}
		fmt.Println("n is", n)
		n++
	}
}

The range Loop

The range clause iterates over elements of a slice, array, string, or map, giving you the index (or key) and the value on each pass. It's the idiomatic way to loop over a collection in Go.

package main

import "fmt"

func main() {
	fruits := []string{"apple", "banana", "cherry"}

	for index, fruit := range fruits {
		fmt.Println(index, fruit)
	}

	// If you only need the value, discard the index with _
	for _, fruit := range fruits {
		fmt.Println("I like", fruit)
	}
}

break and continue

break immediately exits the innermost loop. continue skips the rest of the current iteration and moves on to the next one.

package main

import "fmt"

func main() {
	for i := 1; i <= 10; i++ {
		if i%2 != 0 {
			continue // skip odd numbers
		}
		if i > 6 {
			break // stop once we pass 6
		}
		fmt.Println(i)
	}
}

Labeled break and continue

When loops are nested, a plain break or continue only affects the innermost loop. To control an outer loop from inside a nested one, use a label.

package main

import "fmt"

func main() {
outer:
	for i := 0; i < 3; i++ {
		for j := 0; j < 3; j++ {
			if j == 1 {
				continue outer
			}
			fmt.Println(i, j)
		}
	}
}

Here, continue outer skips straight to the next iteration of the outer loop as soon as j reaches 1, rather than just skipping the rest of the inner loop.

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

You've now mastered every style of Go's single, flexible for loop, along with break, continue, and labeled loop control. Next, you'll learn how switch statements offer a cleaner alternative to long else-if chains for multi-way branching.