Defining with fn
- Rust course
- Beginner
- Lesson 30/115
- 4 min
Define functions with the fn keyword.
Defining functions
Functions are defined with fn; names are written in snake_case. Definition order doesn't matter; a function defined after main can be called inside main.
fn main() {
selam_ver();
}
fn selam_ver() {
println!("Merhaba!");
}Functions that return no value actually return () (unit).
Why functions?
A function binds a repeated job to a name: the code is written once, called from many places and fixed in one place. A good function does one job and its name says so (kdv_ekle, gecerli_mi). Rust has no default parameters or overloading; different behaviors get different names.
Practice Frame
Let fn cizgi() print "----------". In main, call cizgi(), then println!("Rapor");, then cizgi() again.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn cizgi() {
println!("----------");
}
fn main() {
cizgi();
println!("Rapor");
cizgi();
}Expected output
---------- Rapor ----------
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 In which style are function names written in Rust?
- SCREAMING_CASE
- snake_case Correct answer
- camelCase
- PascalCase
Explanation: Functions and variables use snake_case, types PascalCase, constants SCREAMING_SNAKE_CASE; the compiler warns about names that break this.
2 Function keyword
____ cizgi() {
println!("----------");
}fn cizgi() {
println!("----------");
}Explanation: The fn keyword defines a new function.
3 Name and style
| Term | Meaning |
|---|---|
hesapla_toplam |
Function (snake_case) |
HesapMakinesi |
Type (PascalCase) |
MAKS_DEGER |
Constant |
() |
Return of a function returning nothing |