# Control Flow — Go (Golang)

Source: https://www.skillbyai.com/en/go/b-control

> if, for, switch.

## One loop, flexible switch

Go has a single loop keyword, `for`, used as a classic three-part loop, a while-style loop (`for cond {}`), an infinite loop (`for {}`), and with `range` over slices, maps, strings, channels, and integers (`for i := range 5`). `if` can include a short statement (`if err := f(); err != nil`). `switch` needs no `break`, cases can be expressions, and a switch with no value works like a chain of if/else.

## Loops and a value-less switch, run

I ran this with Go 1.27.1 (`go run .` in a module named demo, standard library only). A counting loop, a while-style loop halving n, and a range loop calling a switch-based grade function.

```go
package main

import "fmt"

func grade(score int) string {
	switch {
	case score >= 90:
		return "A"
	case score >= 75:
		return "B"
	default:
		return "C"
	}
}

func main() {
	for i := 1; i <= 3; i++ { // the only loop keyword is for
		fmt.Print(i, " ")
	}
	fmt.Println()
	n := 10
	for n > 1 { // "while" style
		n /= 2
	}
	fmt.Println("n =", n)
	for _, s := range []int{95, 80, 60} {
		fmt.Print(grade(s), " ")
	}
	fmt.Println()
}
```

Output:

```
1 2 3 
n = 1
A B C
```

## Use if with a short statement

if v, err := f(); err != nil { ... } keeps variables scoped to where they are needed.

**Quiz:** How do you write a while loop in Go?

- [ ] while condition { ... }
- [x] for condition { ... }
- [ ] do { } while
- [ ] loop until condition

*Answer:* for condition { ... }. for covers every loop form.