for loop

Learn for, Go's only loop construct.

The for loop

Go's only loop keyword is for; it has three forms:

for i := 0; i < 3; i++ {   // classic
    fmt.Println(i)
}

n := 1
for n < 100 {              // like while
    n *= 2
}

for {                      // infinite loop
    break
}

There is no while or do-while; everything is written with for.

The loop variable

In the classic form, i := 0 is the start, i < 3 the condition and i++ the step after each iteration. The loop variable exists only inside the loop. Since Go 1.22 every iteration gets its own copy of i, so goroutines and closures started inside the loop can safely use i.

Exercise Factorial

Write the faktoriyel(n int) int function with a for loop. Print the result of faktoriyel(5).

Show example solution

package main

import "fmt"

func faktoriyel(n int) int {
    sonuc := 1
    for i := 2; i <= n; i++ {
        sonuc *= i
    }
    return sonuc
}

func main() {
    fmt.Println(faktoriyel(5))
}

Test yourself

After <code>n := 1; for n < 100 { n *= 2 }</code>, what is n?
- 128
- 64
- 100
- 99
Show answer

128 — n goes 1, 2, 4, ..., 64; since 64 < 100 it doubles once more and the loop stops at 128.

Condition

for i := 1; i ____ 5; i++ {
    fmt.Print(i, " ")
}  // 1 2 3 4 5

Show answer

for i := 1; i <= 5; i++ {
    fmt.Print(i, " ")
}  // 1 2 3 4 5

Loop form

for i := 0; i < n; i++

Counter-based
for kosul

Like while
for {}

Infinite
for i, v := range s

Iterating a collection

Next lesson: Iterating with range

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