Introducing Go

Chapter 4. Control Structures

Now that you know how to use variables, it’s time to start writing some useful programs. First, let’s write a program that counts to 10, starting from 1, with each number on its own line. Using what you’ve learned so far, you could write this:

package main

import "fmt"

func main() {
    fmt.Println(1)
    fmt.Println(2)
    fmt.Println(3)
    fmt.Println(4)
    fmt.Println(5)
    fmt.Println(6)
    fmt.Println(7)
    fmt.Println(8)
    fmt.Println(9)
    fmt.Println(10)
}

Or this:

package main
import "fmt"

func main() {
  fmt.Println(`1
2
3
4
5
6
7
8
9
10`)
}

But both of these programs are pretty tedious to write. What we need is a way of doing something multiple times.

The for Statement

The for statement allows us to repeat a list of statements (a block) multiple times. Rewriting our previous program using a for statement looks like this:

package main

import "fmt"

func main() {
    i := 1
    for i <= 10 {
        fmt.Println(i)
        i = i + 1
    }
}

First, we create a variable called i that we use to store the number we want to print. Then we create a for loop by using the keyword for, providing a conditional expression that is either true or false and finally supplying a block to execute. The for loop works like this:

1. We evaluate (run) the expression i <= 10 (“i less than or equal to 10”). If this evaluates to true, then we run the statements inside of the block. Otherwise, we jump to the next line of our program after the block (in this case, there is nothing after the for loop, so we exit the program).