Go for Loop
In Programming, a for-loop (or simply for loop) is a control flow statement for specifying iteration, which allows code to be executed repeatedly.
In this tutorial, we are going to print the multiplication table of a number given by the user. You can already do this without the use of a loop, but it is a lot of work.
package main
import "fmt"
func main() {
var number int
fmt.Print("Enter a number: ")
fmt.Scan(&number)
fmt.Printf("%d * 1 = %d\n", number, number*1)
fmt.Printf("%d * 2 = %d\n", number, number*2)
fmt.Printf("%d * 3 = %d\n", number, number*3)
fmt.Printf("%d * 4 = %d\n", number, number*4)
fmt.Printf("%d * 5 = %d\n", number, number*5)
fmt.Printf("%d * 6 = %d\n", number, number*6)
fmt.Printf("%d * 7 = %d\n", number, number*7)
fmt.Printf("%d * 8 = %d\n", number, number*8)
fmt.Printf("%d * 9 = %d\n", number, number*9)Here a lot of code is repeated, and we designed computers specifically to avoid repeating tasks, so there must be a better way.
The for loop
The for loop is a way to repeat a block of code a certain number of times while keeping track of the index of the current iteration.
for i := 0; i < 10; i++ {
// do something
}It reads: "starting with i equal to 0, repeat the block of code until i is equal to 10, and increment i by 1 each time".
Note: i++, i += 1 and i = i + 1 are all equivalent ways to increment i by 1.
Our multiplication table program can be rewritten as follows:
package main
import "fmt"
func main() {
var number int
fmt.Print("Enter a number: ")
fmt.Scan(&number)
for i := 1; i <= 9; i++ {
fmt.Printf("%d * %d = %d\n", number, i, number*i)
}
}Way cleaner, isn't it?
Output
Enter a number: 4
4 * 1 = 4
4 * 2 = 8
4 * 3 = 12
4 * 4 = 16
4 * 5 = 20
4 * 6 = 24
4 * 7 = 28
4 * 8 = 32
4 * 9 = 36More advanced examples on for loop
While the previous example covers 90% of the use cases of the for loop, there are a few more examples worth mentioning.
Iterating backwards
for i := 10; i > 0; i-- {
// do something
}i-- is similar to i++, but it decrements i by 1 instead of incrementing it.
Iterating over even numbers
for i := 0; i < 10; i += 2 {
// do something
}Infinite loops
Sometimes you want a program to run forever, for example, a web server. An infinite loop is a right tool for the job. You could write it like this:
for i := 0; i < 1, i = 0 {
// do something
}But there is a better way:
for {
// do something
}