How to use for and foreach loop in Golang?

Last Updated : 10 May, 2020

There is only one looping construct in Golang, and that is the for loop. The for loop in Golang has three components, which must be separated by semicolons (;), those are:

The initialization statement: which is executed before the first iteration. e.g. i := 0
The condition expression: which is executed just before every iteration. e.g. i < 5
The Post statement: which is executed at the end of every iteration. e.g. i++

There is no need for any parentheses for enclosing those three components, but to define a block we must use braces { }.

for i := 0 ; i < 5 ; i++{
         // statements to execute......
}

The initialization and post statements are optional.

i:=0
for ; i < 5;{
i++
}

You can use for loop as while loop in Golang. Just drop all the semicolons.

i := 0
for i < 5 {
i++
}

Infnite Loop: If there is no condition statement, the loop becomes an infinite loop.

for {
}

Example:

package main
  
import "fmt"
  
// function to print numbers 0
// to 9 and print the sum of 0 to 9
func main() {
  
    // variable to store the sum
    sum := 0
  
    // this is a for loop which runs from 0 to 9
    for i := 0; i < 10; i++ {
  
        // printing the value of 
        // i : the iterating variable
        fmt.Printf("%d ", i)
  
        // calculating the sum
        sum += i
    }
    fmt.Printf("\nsum = %d", sum)
}

Output:

0 1 2 3 4 5 6 7 8 9 
sum = 45

In Golang there is no foreach loop instead, the for loop can be used as “foreach“. There is a keyword range, you can combine for and range together and have the choices of using the key or value within the loop.

Syntax:

for <key>, <value> := range <container>{

}

Here,

key and value: It can be any variable you want to choose.
container: It can be any variable which is an array, list, map, etc.

Example 1:

package main
  
import "fmt"
  
// Driver function to show the
// use of for and range together
func main() {
  
    // here we used a map of integer to string
    mapp := map[int]string{1: "one", 2: "two", 3: "three"}
  
    // integ act as keys of mapp
    // spell act as the values of
    // mapp which is mapped to integ
  
    for integ, spell := range mapp {
  
        // using integ and spell as
        // key and value of the map
        fmt.Println(integ, " = ", spell)
    }
}

Output:

1  =  one
2  =  two
3  =  three

Example 2:

package main
  
import "fmt"
  
// Driver function to show the
// use of for and range together
func main() {
  
    // declaring an array of integers
    arra := []int{1, 2, 3, 4}
  
    // traversing through the array
    for index, itr := range arra {
      
        // the key or value variables
        // used in for syntax
        // depends on the container. 
        // If its an array or list,
        // the key refers to the index...
        fmt.Print(index, " : ", itr, "\n")
    }
  
    // if we use only one 
    // variable in the for loop,
    // it by default refers to 
    // the value in the container.
    for itr := range arra {
  
        fmt.Print(it, " ")
    }
}

Output:

My Personal Notes

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