Control flow

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Goal

Branch and loop in Go. After this page you will recognise every if and for you meet later in the tier.

Prerequisites

• Types and variables

if and for are the whole thing

Go has two control-flow keywords you need now: if and for. There is no while, no do…while. The for keyword covers every loop shape.

• if — a boolean condition with no surrounding parentheses.
• for init; cond; post — the classic three-clause loop.
• for cond — the same for, used as a while.
• for index, value := range slice — iterate a slice, map, or string.

Code

package main

import "fmt"

func main() {
	// if
	age := 21
	if age >= 18 {
		fmt.Println("adult")
	} else {
		fmt.Println("minor")
	}

	// classic for
	sum := 0
	for i := 1; i <= 5; i++ {
		sum += i
	}
	fmt.Println("sum 1..5:", sum)

	// for as while
	n := 1
	for n < 16 {
		n *= 2
	}
	fmt.Println("doubled past 16:", n)

	// for-range over a slice
	prices := []int{4, 2, 5}
	for index, price := range prices {
		fmt.Printf("item %d costs %d\n", index, price)
	}
}

Run it:

go run main.go

Output:

adult
sum 1..5: 15
doubled past 16: 16
item 0 costs 4
item 1 costs 2
item 2 costs 5

The _ blank identifier discards a value. Write for _, price := range prices when you don't need the index.

Next → Functions