Function

Example of function.

src/03-function/main.rs

fn main() {
    let x = 3;
    let y = 4;
    let result = add(x, y);
    println!("{x} + {y} = {result}");
}

fn add(input1: i32, input2: i32) -> i32 {
    input1 + input2 // notice the omission of `;` at the end.
                    // last statement implicitly returns, and equivalent to
                    // return input1 + input2;
}

danger

In the above example, ff we assign x, and y both to be 2147483647 (max i32), the result will overflow i32 range. Unfortunately, such errors are not caught compile time.

Check out helper methods: wrapping_add, saturating_add, overflowing_add, checked_add.

Calculate area of a circle

Another example where we calculate area of a circle with the input radius given by the user.

src/03-circle-area/main.rs

use std::io;

fn main() {
    println!("Enter radius: ");
    let mut radius = String::new();

    io::stdin()
        .read_line(&mut radius)
        .expect("Failed to read input!");

    let radius: f64 = radius.trim().parse().expect("Please type a number!");
    const PI: f64 = 3.14159;
    let area = PI * radius * radius;

    println!("Area = {area}");
}