Guessing Game - Random Numbers & Game Loops in Rust | Rust by Examples (Lesson 3)

Guessing Game - Random Numbers & Game Loops in Rust

Build a simple interactive number guessing game in Rust by leveraging external crates, random number generation, and control flow constructs. This example demonstrates how to add dependencies, generate a secret number, handle user input, and use pattern matching to guide the player toward the correct guess.

Code

use rand::Rng;                     // Trait for random number generation
use std::cmp::Ordering;             // For comparing values
use std::io;                       // For reading user input

fn main() {
  println!("Guess the number!");

  // Generate a random secret number between 1 and 100 (inclusive)
  let secret_number = rand::thread_rng().gen_range(1..=100);

  loop {
    println!("Please input your guess.");

    let mut guess = String::new();

    // Read user input from stdin
    io::stdin()
      .read_line(&mut guess)
      .expect("Failed to read line");

    // Convert input string to unsigned 32-bit integer, handle parse errors
    let guess: u32 = match guess.trim().parse() {
      Ok(num) => num,
      Err(_) => {
        println!("Please enter a valid number!");
        continue;  // Restart loop if input invalid
      }
    };

    println!("You guessed: {}", guess);

    // Compare guess to secret number
    match guess.cmp(&secret_number) {
      Ordering::Less => println!("Too small!"),
      Ordering::Greater => println!("Too big!"),
      Ordering::Equal => {
        println!("You win!");
        break;  // Exit loop when guessed correctly
      }
    }
  }
}

Key Points

• Use cargo add rand to add the rand crate for random number generation.
• Generate random numbers with rand::thread_rng().gen_range(start..=end) for inclusive ranges.
• Compare values using std::cmp::Ordering and handle outcomes with match expressions.
• Create interactive loops with loop and exit them using break when conditions are met.
• Read and parse user input safely, handling invalid inputs gracefully to keep the game running smoothly.