Functions

Functions are a fundamental building block in Rust. They allow you to encapsulate code into reusable blocks. Functions are defined using the fn keyword, followed by the function name, parameters, and the body of the function.

Defining a Function

fn main() {
    println!("Hello, world!");
}

main is a special function that serves as the entry point of a Rust program.

Function Parameters

Functions can take parameters, which are specified in the parentheses after the function name.

fn greet(name: &str) {
    println!("Hello, {}!", name);
}

fn main() {
    greet("Alice");
    greet("Bob");
}

The greet function takes a single parameter name of type &str.

Return Values

Functions can also return values. The return type is specified after an arrow (->).

fn add(a: i32, b: i32) -> i32 {
    a + b
}

fn main() {
    let sum = add(5, 3);
    println!("Sum: {}", sum);
}

The add function takes two parameters of type i32 and returns their sum, which is also of type i32.

Early Returns

You can return a value early from a function using the return keyword:

fn is_even(num: i32) -> bool {
    if num % 2 == 0 {
        return true;
    }
    false
}

fn main() {
    let number = 4;
    if is_even(number) {
        println!("{} is even", number);
    } else {
        println!("{} is odd", number);
    }
}

The is_even function returns true if the number is even and false otherwise.