Summary - Pointer

Write a counter increment function with & and *.

Pointers summary

&x takes an address, *p reads/writes the value at the address, *T is a pointer type and its zero value is nil. Pointers are for changing values and for sharing large values without copying; they are created with new(T) or &T{...}; don't forget nil checks. Go has no pointer arithmetic, and returning the address of a local variable is safe.

A linked list example

A classic use of pointers is nodes linked to each other:

type Dugum struct {
    Deger int
    Sonraki *Dugum
}

bas := &Dugum{1, &Dugum{2, &Dugum{3, nil}}}
for d := bas; d != nil; d = d.Sonraki {
    fmt.Print(d.Deger, " ")
}
// 1 2 3

The last node's Sonraki field is nil; the loop ends when it reaches nil.

Exercise Linked list sum

Write the Dugum type above. Build the list 1 → 2 → 3 → 4 and compute and print the sum of its values with a loop.

Show example solution

package main

import "fmt"

type Dugum struct {
    Deger   int
    Sonraki *Dugum
}

func main() {
    bas := &Dugum{1, &Dugum{2, &Dugum{3, &Dugum{4, nil}}}}
    toplam := 0
    for d := bas; d != nil; d = d.Sonraki {
        toplam += d.Deger
    }
    fmt.Println(toplam)
}

Test yourself

If you pass a slice to a function and set <code>s[0] = 9</code> inside, does the caller's slice change?
- Yes; the slice shares the underlying array, no pointer needed
- No, a copy is taken
- Only with *[]int
- It doesn't compile
Show answer

Yes; the slice shares the underlying array, no pointer needed — The slice header is copied but points to the same array, so element changes are visible. Length changes via append, however, aren't.

Next node

for d := bas; d != nil; d = d.____ {
    toplam += d.Deger
}

Show answer

for d := bas; d != nil; d = d.Sonraki {
    toplam += d.Deger
}

Group summary

&x

Address
*p

Value
new(T)

Zero-valued allocation
nil

No value

Next lesson: Struct declaration

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