Loops

Loops

Go has only one looping construct, the for loop.

The basic for loop has three components separated by semicolons:

• 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 will often be a short variable declaration, and the variables declared there are visible only in the scope of the for statement.

The loop will stop iterating once the boolean condition evaluates to false.

Note: Unlike other languages like C, Java, or JavaScript there are no parentheses surrounding the three components of the for statement and the braces { } are always required

Examples

The following code prints numbers from 1 to 9.

package main

import "fmt"

func main() {
    for i := 0; i < 10; i++ {
        fmt.Println(i)
    }
}

You can omit the init and post statement in the for loop to get a while loop. The below loop works like a while loop

package main

import "fmt"

func main() {
    i := 0

    for i < 10 {
        fmt.Println(i)
        i++
    }
}

Golang also provides a for-range loop to loop over an array, slice or few other datastructures.

The for-range loop provides us access to the index and value of the elements in the array or slice we are looping through as shown below

package main

import "fmt"

func main() {
    myList := []int{1,2,3}

    for index, value := range myList {
        fmt.Printf("%d is index, %d is value", index, value)
    }
}

We can ignore one or both the fields in a for-range loop by giving an _ instead of giving a variable name

    for _, value := range myList {
        fmt.Println(value)
    }

Exercise

Find the sum of numbers from 1 to 100 using a for loop