Showcases integer addition using a function in Rust...

integer_addition.rs

use std::io;

fn add(x: int, y: int) -> int { // takes two integers and returns an integer
    x + y
}

fn main() {
    println!("Simple Addition Calculator, written in Rust!");

    println!("Enter 1st number: ");
    let a_input = io::stdin()
            .read_line() // read user entered input
            .ok().expect("There was a problem reading your input."); // output this in case of a problem
    let a_optnum: Option<int> = from_str(a_input.as_slice().trim()); // convert our input string to an Option<int>
    let a = match a_optnum {
        Some(a) => a, // strip Option from Option<int>, leaving an int
        None    => {
            println!("There's no operand!"); // In case there's no number, display this
            return; // try again
        }
    };

    println!("Enter 2nd number: ");
    let b_input = io::stdin()
            .read_line()
            .ok().expect("There was a problem reading your input.");
    let b_optnum: Option<int> = from_str(b_input.as_slice().trim());
    let b = match b_optnum {
        Some(b) => b,
        None    => {
            println!("There's no operand!");
            return;
        }
    };

    // finally, add the two numbers
    let result = add(a, b); // notice the ';', otherwise we would  end up with a '()' type
    // print out the result
    println!("{} + {} = {}", a, b, result);
}