There is only one keyword to perform loops in Go: for. The implementation is very flexible. In this article, we’ll consider the various ways to use it. If you’re interested in the details, you should definitely go through the official specification.
For loops in Go
First, let’s see how to replicate the common C-style for loop. In Go, it works similar to other languages. We supply 3 statements after the keyword. The first is an initial statement to run, the second is the condition that is evaluated before each iteration and the third is run at the end of an iteration.
package main
import "fmt"
func main() {
for i := 1; i <= 10; i++ {
fmt.Println(i)
}
}
1
2
3
4
5
6
7
8
9
10
While Loops in Go
In most computer programming languages, a while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.
In Go, we use the for
keyword to write a while loop by providing only a single statement. The loop will continue to run as long as the statement is true.
package main
import "fmt"
func main() {
var a = 1
for a <= 5 {
fmt.Printf("a is: %v \n", a)
a++
}
}
a is: 1
a is: 2
a is: 3
a is: 4
a is: 5
The Range Clause
The range
clause allows us to iterate over an array, slice, map, string, or channel.
Looping over an array using range
When we use range
to loop over an array, we will receive 2 values for each iteration. The index of each element and a copy of the value. Receiving the 2nd value is optional.
package main
import "fmt"
func main() {
var myArray = [...]int{1,2,3,4}
for k, v := range myArray {
fmt.Printf("index=%v, value=%v \n", k, v)
}
}
index=0, value=1
index=1, value=2
index=2, value=3
index=3, value=4
Looping over a slice using range
Just like with an array, when we use range
to loop over a slice, we will receive 2 values for each iteration. The index of each element and a copy of the value. Receiving the 2nd value is optional.
package main
import "fmt"
func main() {
var mySlice = []int{1,2,3,4}
for k, v := range mySlice {
fmt.Printf("index=%v, value=%v \n", k, v)
}
}
index=0, value=1
index=1, value=2
index=2, value=3
index=3, value=4
Looping over a map using range
As you may expect, when we loop over a map using range
, we also receive 2 values. This time the values are the key of the element in the map and a copy of the value. Receiving the 2nd value is optional.
package main
import "fmt"
func main() {
var myMap = map[string]string{
"foo": "bar",
"boo": "baz",
}
for k, v := range myMap {
fmt.Printf("key=%v, value=%v \n", k, v)
}
}
key=foo, value=bar
key=boo, value=baz
Looping over a string using range
When we loop over a string using range
, we also receive 2 values in each iteration. The first value is the byte position where the character begins, the second value is a rune
which represents a single Unicode character. As usual, receiving the 2nd value is optional.
package main
import "fmt"
func main() {
var myString = "Stephen"
for index, runeValue := range myString {
fmt.Printf("%#U starts at byte position %d\n", runeValue, index)
}
}
U+0053 'S' starts at byte position 0
U+0074 't' starts at byte position 1
U+0065 'e' starts at byte position 2
U+0070 'p' starts at byte position 3
U+0068 'h' starts at byte position 4
U+0065 'e' starts at byte position 5
U+006E 'n' starts at byte position 6
Looping over a channel using range
When we loop over a channel using range
, we receive a single value, which is the next element in the channel.
package main
import "fmt"
func main() {
queue := make(chan string, 2)
queue <- "one"
queue <- "two"
close(queue)
for elem := range queue {
fmt.Println(elem)
}
}
one
two
Conclusion
We’ve seen the various loop mechanics in Go. Now Go forth and prosper. .
The post Loops in Go appeared first on Stephen AfamO's Blog.
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