func declaration

Learn to declare functions with the func keyword.

Defining functions

A function is defined with the func keyword: the name, parameters in parentheses, then the return type and the body in curly braces.

func selam(ad string) string {
    return "Merhaba " + ad
}

fmt.Println(selam("Ada"))  // Merhaba Ada

Functions starting with an upper-case letter (Selam) can be called from outside the package; lower-case ones only within it.

Why functions?

Writing repeated code once and calling it by name reduces mistakes and makes reading easier. A good function does one job and its name describes it: kdvEkle, ortalama, gecerliMi. In Go, functions can't be defined inside other functions (except anonymous ones), and there is no overloading (same name, different parameters).

Exercise Square function

Write the kare(n int) int function and print the result of kare(7).

Show example solution

package main

import "fmt"

func kare(n int) int {
    return n * n
}

func main() {
    fmt.Println(kare(7))
}

Test yourself

What does a function with no return type return?
- It doesn't compile
- Nothing; its return statement takes no value
- 0
- nil
Show answer

Nothing; its return statement takes no value — Functions like func yaz(s string) { fmt.Println(s) } return no value; a bare return is used to leave early.

Return a value

func kare(n int) int {
    ____ n * n
}

Show answer

func kare(n int) int {
    return n * n
}

Function part

func

Definition keyword
(ad string)

Parameter
string (after the parentheses)

Return type
return

Gives the result

Next lesson: Parameters and return

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