Lesson 7 · 7 of 20

Choosing with switch · Go

Choose between several cases with switch in Go: several values per case, default, switch with no expression, init statement and fallthrough.

Go · Choosing with switch in DMarlon Studio: the example's code and its output in the terminal

switch compares a value with several cases and runs the first one that matches. switch day looks at the value of day; a case can list several values separated by commas, like "Saturday", "Sunday", and default runs when none of them matches.

Unlike C or JavaScript, in Go each case ends on its own: there is no need for break, and execution never slips into the next case by accident.

A switch with no value is a tidier way to write a chain of if and else if: each case holds a condition and the first true one wins. With 82 points score >= 90 does not hold, but score >= 80 does, so the grade is a B.

Like if, switch accepts an init statement: switch level := 2; level. And if you really want to carry on into the next case, you have to ask for it with fallthrough: after level 2, case 1 runs too, without being checked.

Code · main.go

package mainimport "fmt"func main() {	day := "Saturday"	// Each case ends on its own: no break needed.	switch day {	case "Saturday", "Sunday":		fmt.Println(day, "is weekend")	default:		fmt.Println(day, "is a working day")	}	// With no value, switch works like a chain of if / else.	score := 82	switch {	case score >= 90:		fmt.Println(score, "-> grade A")	case score >= 80:		fmt.Println(score, "-> grade B")	default:		fmt.Println(score, "-> grade C")	}	// An init statement, and fallthrough to run the next case too.	switch level := 2; level {	case 2:		fmt.Println("Level 2: bonus unlocked")		fallthrough	case 1:		fmt.Println("Level 1: basics done")	}}

Output · go run main.go

Saturday is weekend
82 -> grade B
Level 2: bonus unlocked
Level 1: basics done

Key points

switch value looks for the first matching case.
A case can list several values separated by commas.
No break needed; fallthrough moves on to the next case.
switch with no value replaces an if / else if chain.
default runs when no case matches.

Exercise

Write a switch on a month number (1 to 12) that prints the season (winter, spring, summer or autumn), with several months in each case and a default for invalid numbers.