Go For Loop

A for loop is a loop that repeats a block of code. One for header can hold the start, the condition, and the change for a counter.

Counting with three parts

The counter starts at 1 and grows by 1 each pass. The loop stops after printing 3.

package main

import "fmt"

func main() {
	for i := 1; i <= 3; i++ {
		fmt.Println(i)
	}
}

A condition only loop

This header holds only a condition. The counter changes inside the block instead.

package main

import "fmt"

func main() {
	i := 3
	for i >= 1 {
		fmt.Println(i)
		i--
	}
}

Stepping by two

The change part adds 2 after each pass. The counter prints the even numbers up to 8.

package main

import "fmt"

func main() {
	for i := 2; i <= 8; i += 2 {
		fmt.Println(i)
	}
}

Nested loops build rows

The inner loop prints three stars with no new line. The print after it ends the row.

package main

import "fmt"

func main() {
	for row := 1; row <= 2; row++ {
		for col := 1; col <= 3; col++ {
			fmt.Print("*")
		}
		fmt.Println()
	}
}

Example

package main

import "fmt"

func main() {
	for i := 1; i <= 3; i++ {
		fmt.Println("7 x", i, "=", (7 * i))
	}
}

Key points

The classic header holds three parts split by semicolons.
The first part sets the starting value of the counter.
The second part is the condition checked before each pass.
The third part changes the counter after each pass.
A for loop with only a condition leaves out the start and change parts.
A nested loop is a loop inside a loop, and the inner loop runs fully on each outer pass.

In this example, i starts at 1. The first pass prints "7 x 1 = 7". The second pass prints "7 x 2 = 14". The third pass prints "7 x 3 = 21". The condition then fails and the loop stops.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Go Playground

package main

import "fmt"

func main() {
	for i := 1; i <= 3; i++ {
		fmt.Println("7 x", i, "=", (7 * i))
	}
}

Exercise

Which part of a classic for header runs after each pass?

The third part The first part The condition The loop block