Iterating with range
- Go course
- Beginner
- Lesson 37/90
- 4 min
Learn to loop over slices and maps with range.
Iterating with range
range iterates over slices, arrays, maps, strings and channels. For slices it gives the index and value on each iteration:
meyveler := []string{"elma", "armut", "kiraz"}
for i, m := range meyveler {
fmt.Println(i, m)
}
for _, m := range meyveler { // value only
fmt.Println(m)
}Since Go 1.22, for i := range 5 also counts from 0 to 4.
range over maps and strings
On a map, range gives the key and value; the order is random and may change on every run. On a string it gives the byte index and the rune:
stok := map[string]int{"kalem": 3, "defter": 5}
for ad, adet := range stok {
fmt.Println(ad, adet)
}
for i, r := range "çay" {
fmt.Println(i, string(r)) // 0 ç, 2 a, 3 y
}If ordered output is needed, collect the map keys into a slice and sort them first.
Practice Double the slice
Declare s := []int{1, 2, 3}. Double every element in place with a for i := range s loop and print the slice.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func main() {
s := []int{1, 2, 3}
for i := range s {
s[i] *= 2
}
fmt.Println(s)
}Expected output
[2 4 6]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Does <code>for _, v := range s { v *= 2 }</code> change the slice?
- Yes, every element doubles
- Only the first element changes
- It doesn't compile
- No; v is a copy of the element Correct answer
Explanation: To change the slice, write through the index: for i := range s { s[i] *= 2 }.
2 Skip the index
for ____, m := range meyveler {
fmt.Println(m)
}for _, m := range meyveler {
fmt.Println(m)
}Explanation: _ ignores the unused index.
3 range target
| Term | Meaning |
|---|---|
[]string |
index, value |
map[K]V |
key, value |
string |
byte index, rune |
range 5 |
0..4 |