Computing total
- Go course
- Beginner
- Lesson 49/90
- 6 min
Compute the cart total with range.
Computing the total
The cart total is the sum of every product's subtotal. Walk the products with range and accumulate:
func (s Sepet) Toplam() float64 {
t := 0.0
for _, u := range s.Urunler {
t += u.AraToplam()
}
return t
}A value receiver is enough here because the cart is only read.
A discount rule
Business rules are added as methods too. For example, a 10% discount on purchases over 100 TL:
func (s Sepet) Odenecek() float64 {
t := s.Toplam()
if t > 100 {
return t * 0.9
}
return t
}Keeping the rule in a separate method means only one place changes when the rule does.
Practice Total and discount
Write Urun (with AraToplam), Sepet, and the Toplam and Odenecek methods. The cart holds Kalem 12.5 × 5 and Çanta 80 × 1; print the total and the amount due on one line.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
type Urun struct {
Ad string
Fiyat float64
Adet int
}
func (u Urun) AraToplam() float64 { return u.Fiyat * float64(u.Adet) }
type Sepet struct{ Urunler []Urun }
func (s Sepet) Toplam() float64 {
t := 0.0
for _, u := range s.Urunler {
t += u.AraToplam()
}
return t
}
func (s Sepet) Odenecek() float64 {
t := s.Toplam()
if t > 100 {
return t * 0.9
}
return t
}
func main() {
s := Sepet{Urunler: []Urun{{"Kalem", 12.5, 5}, {"Çanta", 80, 1}}}
fmt.Println(s.Toplam(), s.Odenecek())
}Expected output
142.5 128.25
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens if <code>t := 0</code> is written instead of <code>t := 0.0</code>?
- The result is rounded
- t becomes nil
- t becomes an int and t += float64 is a compile error Correct answer
- It makes no difference
Explanation: := infers the type from the value; 0 gives int, 0.0 gives float64. Go doesn't mix int and float64.
2 Accumulate
for _, u := range s.Urunler {
t ____ u.AraToplam()
}for _, u := range s.Urunler {
t += u.AraToplam()
}Explanation: t += x adds x to t and writes the result back to t.
3 Cart and result
| Term | Meaning |
|---|---|
Kalem 12.5 × 5 |
62.5 |
Defter 20 × 1 |
20 |
Toplam |
82.5 |
Toplam > 100 |
10% discount |