[Rust] Secret Number game demo

// Call rand package for random number generation
extern crate rand;

use std::io;
use std::io::Write;
use rand::Rng;

fn main() {
    // Set the limit of answer
    const MAX: u32 = 100;
    const MIN: u32 = 1;

    // Set the limit of user input
    let mut upper = MAX;
    let mut lower = MIN;

    // Get a random number between MIN and MAX
    let answer = rand::thread_rng().gen_range(MIN, MAX + 1);

    loop {
        // Prompt for user input
        print!("Input a number ({}-{}):", lower, upper);
        // Flush standard out
        let _ = io::stdout().flush();

        // Receive user input
        let mut input = String::new();
        io::stdin()
            .read_line(&mut input)
            .expect("Failed to read from stdin");

        // Parse integer
        let guess = match input.trim().parse::<u32>() {
            Ok(n) => n,
            Err(_) => {
                println!("Not a valid number");
                continue;
            }
        };

        // Check the range of the guess
        if guess < lower || guess > upper {
            println!("The number should be between {} and {}",
                     lower, upper);
            continue;
        }

        // Check whether the guess is correct
        if guess == answer {
            println!("You got it!");
            break;
        } else if guess > answer {
            println!("Too large");
            upper = guess;
        } else {  // guess < answer
            println!("Too small");
            lower = guess;
        }
    }
}