[The Rust Programming Language] Ch. 2: Programming a Guessing Game

https://rust-book.cs.brown.edu/ch02-00-guessing-game-tutorial.html

Programming a Guessing Game - The Rust Programming Language

Setting Up a New Project

$ cargo new guessing_game
$ cd guessing_game

cargo new creates a new cargo project with a name as the argument.

Processing a Guess

use std::io; can be used to process the input.

println! is a macro for printing string to a screen

Storing Values with Variables

let can be used to create a variable.

mut makes the variable to be mutable. Every object in Rust is mutable by default

Associated function is a function that’s implemented on a type. :: is used to describe the associated function.

• ex) String::new()

Receiving User Input

io::stdin().read_line(&mut guess) can be used to harness user input.

• guess is where the value read will be stored and it is referenced by &. &mut references and mutates the data.

Handling Potential Failure with Result

Result is used to handle error

• Ok indicates the operation was successful, and it contains the generated value
• Err means that the operation failed, and it contains information about how or why the operation failed.
• using expect method allows for the handling of Err without needing for program to crash

Printing Values with println! Placeholders

{} can hold value in place.

• a variable can go into the place
• println!("You guessed: {guess}");
• if the brackets are left blank, a comma-separated list can be followed to go in place of curly brackets
• let x = 5; let y = 10; println!("x = {x} and y + 2 = {}", y + 2);

Testing the First Part

cargo run can be used to run the rust file.

Using a Crate to Get More Functionality

Since Rust does not provide a standard library for randomness, rand crate must be used.

library crate: code that is intended to be used in other programs and can’t be executed on its own

binary crate: code that is executable

[dependencies]
rand = "0.8.5"

Adding line above in Cargo.toml file can add dependencies to the programs.

Running cargo build after adding rand crate to the file downloads and compiles the dependencies.

• Running the code once again does nothing because Rust knows that nothing has been changed

**Cargo.lock** file records all the dependencies’ versions used in the program, and this is for reproducibility.

Generating a Random Number

let secret_number = rand::thread_rng().gen_range(1..=100);

gen_range function takes in range as input and returns a random number in that range.

• 1..=100 is used to represent a range of numbers between 1 and 100, inclusive

Comparing the Guess to the Secret Number

by using std::cmp::Ordering type, can be used to get variants Less, Greater, Equal.

match guess.cmp(&secret_number) {
    Ordering::Less => println!("Too small!"),
    Ordering::Greater => println!("Too big!"),
    Ordering::Equal => println!("You win!"),
}

cmp compares a variable to another variable.

match expression decides what operation to execute based on the patterns of the return value

parse method converts numbers automatically based on Rust’s default inference of value.

• only work on characters that can logically be converted into numbers and so can easily cause errors

Allowing Multiple Guesses with Looping

loop keyword creates an infinite loop. It works the same as while True in Python.

break keyword exits the loop when the statement is executed.