Rust: Rust入門と開発環境のセットアップ：この安全で高性能なシステムプログラミング言語について知る

fn main() {
    let msg = String::from("Hello, secure world!");
// Compiler Guarantees: msg memory is automatically released when it goes out of scope.
// Not necessary malloc, nor free
    println!("{}", msg);
}

# Run in the terminal (Windows requires Visual Studio C++ Build Tools to be installed first)
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

rustc --version   # Output: rustc 1.86.0 (05f9846f8 2025-03-31)
cargo --version   # Output: cargo 1.86.0 (version number)

rustup update    # Update to the latest version
rustup self uninstall  # Uninstall (for cache retention, use uninstall rather than directly deleting the directory)

// ============================================
// First Rust Program: Print Hello World
// ============================================

fn main() {
    println!("Hello, world!");
}

Hello, world!

# Create a New Project
cargo new hello_cargo
cd hello_cargo

hello_cargo/
├── Cargo.toml    # Project Configuration File (Dependencies, Metadata)
├── src/
│   └── main.rs   # Source Code Entry Point

[package]
name = "hello_cargo"
version = "0.1.0"
edition = "2021"

cargo build       # Compilation (generates target/debug/ directory)
cargo run         # Compilation + Run

Hello, world!

// ============================================
// A Simple Addition Calculator
// ============================================

fn main() {
    let a: i32 = 10;      // i32 is a 32-bit signed integer
    let b: i32 = 20;      // Rust type annotations use a colon
    let sum = a + b;

    println!("{} + {} = {}", a, b, sum);
}

10 + 20 = 30

// ============================================
// Comprehensive Example: Temperature Conversion + Simple Report Generation
// Demo Variables, Types, Basic Syntax, Such as Formatted Output
// ============================================

fn celsius_to_fahrenheit(celsius: f64) -> f64 {
    celsius * 9.0 / 5.0 + 32.0
}

fn fahrenheit_to_celsius(fahrenheit: f64) -> f64 {
    (fahrenheit - 32.0) * 5.0 / 9.0
}

fn main() {
    let cities = ["Beijing", "Shanghai", "Guangzhou"];
    let temps_c = [28.5, 31.2, 33.8];

    println!("=== City Temperature Report ===");
    println!("{:<12} {:>10} {:>10}", "City", "Celsius(°C)", "Fahrenheit(°F)");
    println!("{}", "-".repeat(34));

    let mut index = 0;
    while index < cities.len() {
        let c = temps_c[index];
        let f = celsius_to_fahrenheit(c);
        println!("{:<12} {:>10.1} {:>10.1}", cities[index], c, f);
        index += 1;
    }

    let freezing_f: f64 = 32.0;
    let freezing_c = fahrenheit_to_celsius(freezing_f);
    println!("\nFreezing Point: {:.1}°F = {:.1}°C", freezing_f, freezing_c);

    const BOILING_C: f64 = 100.0;
    let boiling_f = celsius_to_fahrenheit(BOILING_C);
    println!("Boiling Point: {:.1}°C = {:.1}°F", BOILING_C, boiling_f);
}

=== City Temperature Report ===
City           Celsius(°C)    Fahrenheit(°F)
----------------------------------
Beijing           28.5       83.3
Shanghai          31.2       88.2
Guangzhou         33.8       92.8

Freezing Point: 32.0°F = 0.0°C
Boiling Point: 100.0°C = 212.0°F

use std::io;

fn main() {
    let secret = 42; // Hidden answer (random numbers will be used in subsequent lessons)
    println!("🎯 Guess the Number Game! Range 1-100");

    loop {
        println!("Please enter your guess:");

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

        let guess: i32 = match guess.trim().parse() {
            Ok(num) => num,
            Err(_) => {
                println!("⚠️  Please enter a valid number!");
                continue;
            }
        };

        match guess.cmp(&secret) {
            std::cmp::Ordering::Less => println!("Too small! ⬆️"),
            std::cmp::Ordering::Greater => println!("Too big! ⬇️"),
            std::cmp::Ordering::Equal => {
                println!("🎉 Congratulations, you got it right! The answer is {}", secret);
                break;
            }
        }
    }
}