Golang : For loop continue,break and range



Tags : golang for continue break range

Feeling like writing about FOR loop today so....this tutorial will explore how Golang's FOR loop works.

For loop is a block of code that repeats itself with increase/decrease or changes in input variables until certain condition is met. In the simplest form a for loop looks like this :

 package main

 import "fmt"

 func main() {
 // initialize i to 0 
 // check each time if i is less than 10
 // the increase the value of i by 1 for each loop after the first
 for i := 0; i < 10; i++ {
 fmt.Printf("i is %d\n", i)
 }
 }

Output :

i is 0

i is 1

i is 2

i is 3

i is 4

i is 5

i is 6

i is 7

i is 8

i is 9

Another example but with string value instead of integer

 package main

 import "fmt"

 func main() {

 s := "" // initialize s to empty string
 for s != "eeeee" {  // if s is not 5 e
 fmt.Printf("s is %s\n", s)
 s = s + "e" // add e to s (string value!) and repeat 
 }
 }

Output :

s is

s is e

s is ee

s is eee

s is eeee

Just in case you have multiple counters to take into account for your FOR loop. No problem. See this example

 package main

 import "fmt"

 func main() {
 // multiple counters initialization
 // combine each conditions with &&(and) and ||(or) to form the final boolean condition
 // incrementation of the multiple counters

 for i, j, s := 0, 5, "e"; i < 10 && j < 100 && s != "eeeee"; i, j, s = i+1, j+1, s+"e" {
 fmt.Println("Value of i, j, s:", i, j, s)
 }
 }

break keyword :

Basically break will stop the for loop entirely once a condition is met.

To break the for loop, see this code fragment. (taken from Read until certain condition is met tutorial )

 var userInput []string
 scanner := bufio.NewScanner(os.Stdin)

 for scanner.Scan() {
 line := scanner.Text()
 if line == "." {
 break // to stop writing enter . (period) and press enter
 }
 userInput = append(userInput, line+"\n")
 }

continue keyword

continue is the opposite of break keyword, basically what it allows you to do is to skip when a condition is met and continue with the for loop again.

this code example demonstrate how the continue keyword works in a for loop

 package main

 import "fmt"

 func main() {

 for i := 0; i < 9; i++ {
 if i%2 == 0 {
 continue //skip this part and go back to beginning of for loop
 }
 fmt.Println("The odd number you are looking for :", i)
 }
 }

range keyword :

range allows you to iterate each key/value in an array, slice or map. If used against a map, range will return 2 values - the index(key) and the related values. See example below :

 package main

 import (
 "fmt"
 )

 func main() {
 niceplacestovisit := []string{"Paris", "Kyoto", "Bali", "New York"}

 i := 1

 for cityname := range niceplacestovisit {
 fmt.Printf("[%d] city name is %s\n", i, niceplacestovisit[cityname])
 i++
 }

 fmt.Println("------------------------")
 // range also return 2 values
 // 1st the index or key
 // 2nd the value

 niceplacestovisit2 := map[string]string{"1":"Paris", "2":"Kyoto", "3":"Bali", "4":"New York"}

 for cityname2, value := range niceplacestovisit2 {
 fmt.Printf("[%s] city name is %s\n", cityname2, value)
 }

 // starting from Go 1.4
 // it is ok to iterate without specifying the values

 for range niceplacestovisit2 {
 fmt.Println("Many cities iterated over niceplacestovisit2 array")
 } 



 }

Output :

1 city name is Paris

[2] city name is Kyoto

[3] city name is Bali

[4] city name is New York


1 city name is Paris

[2] city name is Kyoto

[3] city name is Bali

[4] city name is New York

Many cities iterated over niceplacestovisit2 array

Many cities iterated over niceplacestovisit2 array

Many cities iterated over niceplacestovisit2 array

Many cities iterated over niceplacestovisit2 array

Hope this tutorial be useful to you in learning Golang.



Tags : golang for continue break range

By Adam Ng

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