Computing total

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.

Exercise 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.

Show example 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())
}

Test yourself

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
- It makes no difference
Show answer

t becomes an int and t += float64 is a compile error — := infers the type from the value; 0 gives int, 0.0 gives float64. Go doesn't mix int and float64.

Accumulate

for _, u := range s.Urunler {
    t ____ u.AraToplam()
}

Show answer

for _, u := range s.Urunler {
    t += u.AraToplam()
}

Cart and result

Kalem 12.5 × 5

62.5
Defter 20 × 1

20
Toplam

82.5
Toplam > 100

10% discount

Next lesson: Printing the cart

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