Command-line menu
- Go course
- Beginner
- Lesson 28/90
- 6 min
Add a menu with switch and a loop.
Choosing the operation: switch
switch is ideal for picking the right function by the symbol the user entered:
func hesapla(a float64, islem string, b float64) (float64, error) {
switch islem {
case "+":
return topla(a, b), nil
case "-":
return cikar(a, b), nil
case "*":
return carp(a, b), nil
case "/":
return bol(a, b)
default:
return 0, fmt.Errorf("bilinmeyen işlem: %s", islem)
}
}The menu loop
In a real application input is read line by line from the user and the loop continues until they type "çık". fmt.Sscan can split the input into pieces:
var a, b float64
var islem string
n, _ := fmt.Sscan("12 * 3", &a, &islem, &b)
// n == 3, a=12, islem="*", b=3In this lesson you'll try the menu by reading input from a fixed list.
Practice The calculator
Write the hesapla function for + and * only; for other symbols it returns fmt.Errorf("bilinmeyen işlem: %s", islem). Parse the inputs []string{"12 * 3", "2 ^ 3"} with fmt.Sscan and print each result or error.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func hesapla(a float64, islem string, b float64) (float64, error) {
switch islem {
case "+":
return a + b, nil
case "*":
return a * b, nil
default:
return 0, fmt.Errorf("bilinmeyen işlem: %s", islem)
}
}
func main() {
for _, line := range []string{"12 * 3", "2 ^ 3"} {
var a, b float64
var islem string
fmt.Sscan(line, &a, &islem, &b)
sonuc, err := hesapla(a, islem, b)
if err != nil {
fmt.Println(err)
continue
}
fmt.Println(sonuc)
}
}Expected output
36 bilinmeyen işlem: ^
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Do you need to write <code>break</code> at the end of a <code>case</code> in Go?
- Only in the last case
- Only in default
- No; the switch ends automatically after the matching case Correct answer
- Yes, always
Explanation: Go cases don't fall through; to continue to the next one you explicitly write fallthrough.
2 Default branch
switch islem {
case "+":
return a + b, nil
____:
return 0, fmt.Errorf("bilinmeyen işlem")
}switch islem {
case "+":
return a + b, nil
default:
return 0, fmt.Errorf("bilinmeyen işlem")
}Explanation: default runs when no case matches.
3 Input and result
| Term | Meaning |
|---|---|
"12 * 3" |
36 |
"9 / 2" |
4.5 |
"1 / 0" |
division-by-zero error |
"2 ^ 3" |
unknown operation |