Guess The Number in Rust

guess_the_number.rs

#![feature(old_io)]
#![feature(rand)]
#![allow(deprecated)]

use std::cmp::Ordering;
use std::old_io;
use std::rand;

fn cmp(a: u8, b: u8) -> Ordering {
  if a > b {
    Ordering::Greater
  } else if a < b {
    Ordering::Less
  } else {
    Ordering::Equal
  }
}

fn main() {
  let random_num = rand::random::<u8>();
  let mut attempts = 0;

  println!("I am thinking of a random 8-bit integer between 0 and 255.");
  println!("Can you guess it?");

  loop {
    let input = old_io::stdin()
      .read_line()
      .ok()
      .expect("Failed to read input!");

    match input.trim().parse::<u8>() {
      Ok(guess) => {
        attempts += 1;
        match cmp(guess, random_num) {
          Ordering::Greater => {
            println!("Your guess is too big!");
          },
          Ordering::Less => {
            println!("Your guess is too small!");
          },
          Ordering::Equal => {
            if attempts == 1 {
              println!("You got the number on your first try!");
              println!("Were you debugging my process or something?");
            } else {
              println!("You got the number after {} tries!", attempts);
            }
            break;
          }
        }
      },
      Err(_) => {
        println!("That doesn't look like much of a number to me.");
      }
    }
  }
}

I wrote this after going through most of the first chapter of The Rust Programming Language book. The final section of the chapter involves writing a number guessing game and I decided to try writing it myself before reading the section.

The chapter currently uses old_io without explaining why--it looks like the language is going through a bit of redesign as it prepares for its 1.0 release.

I had to do a bit of web searching to find out how to generate random numbers and convert strings to integers, which the chapter hadn't taught me yet.