factorial.rs

use std::io;

fn main() {

    println!("Please input the factorial.");

    let mut s = String::new();

    io::stdin()
        .read_line(&mut s)
        .expect("failed to read line");

    let n: u8 = s.trim().parse().expect("Enter in a positive integer only");
    println!("Factorial of {} = {}", n, factorial(n));
}

// We return an i64 to include bigger numerical results.
fn factorial(n: u8) -> i64 {
    let mut total = n as i64;
    for i in (1..n).rev() {
        // rev() isn't needed and has no effect in this case
        total *= i as i64;
    }

    total
}