freeCodeCamp/guide/english/go/loops/index.md

title
Loops

For loop in Go

Go has only for loop. The basic for loop has three components separated by ; -

• the init statement: executed before the first iteration

• the condition expression: evaluated before every iteration

• the post statement: executed at the end of every iteration

The init statement is often a short variable declaration. The variables declared there are visible only in the scope of the for statement. The loop stops iterating once the boolean condition evaluates to false.

An example of the for loop is given below -

for.go

package main

import "fmt"

func main() {
	sum := 0
	for i := 0; i <= 10; i++ {
		sum += i
	}
	fmt.Println("The sum of first 10 natural numbers is", sum)
}

Running the above program produces an output similar to the following output -

$ go run for.go
The sum of first 10 natural numbers is 55

You can use continue and break to adjust the loops flow

  // this code prints any odd numbers up to 5
  for n := 0; n <= 10; n++ {
    if n % 2 == 0 {
      // if the number is even jump to the next n
      continue
    }
    fmt.Println(n)
    // if the number is 5 exit the loop
    if n == 5 {
      break
    }
  }

If you want to create an infinite loop just use for { }

  for {
    // Whill loop until a condition breaks the loop
    break // exit the loop
  }

Replacement for while-loop

To simulate while-loop of other languages, you can simply exclude the init and post statement:

func main() {
	num := 1
	for num <= 1000 {
		num *= 2
	}
	fmt.Println("The smallest power of 2 above 1000 is", num)
}

Replacement for do-while-loop

The do-while-loop is useful as the statement is executed at least once before the condition is checked and continue until the condition is no longer true. To simulate the do-while-loop of other languages we can use an infinite for loop with a break condition at the end. The traditional do-while has the following syntax.

do {
        statement
} while (condition);

We can simulate this syntax in go as follows:

for {
        statement
        if (!condition) { break }
}

A Go example

x := 0
for {
        // These statements are ran at least once
        x++
        fmt.Println(x)
        
        // Check do the condition at the end. If it is no longer true end the loop
        if !(x < 10) {
                break
        }
}