fn main() {
    let guess: u32 = "42".parse().expect("Not a number!");
    println!("You guessed: {}", guess);
    let heart_eyed_cat = '😻';
    println!("{}", heart_eyed_cat);

    let cc = another_function(3, 'a');
    println!("The value of cc is: {}", cc);

    // Statements and Expressions
    let x = {
        let y = 5;
        y + 1
    };
    println!("The value of x is: {}", x);

    for number in 1..4 {
        println!("{}!", number);
    }

    let result = fibonacci_function(3);
    println!("The result is: {}", result);
    // 相互转换摄氏与华氏温度
    let celsius = 30.0;
    let fahrenheit = celsius_to_fahrenheit(celsius);
    println!("{} celsius is {} fahrenheit.", celsius, fahrenheit);
    let fahrenheit = 86.0;
    let celsius = fahrenheit_to_celsius(fahrenheit);
    println!("{} fahrenheit is {} celsius.", fahrenheit, celsius);

    let mut s = String::from("hello");
    s.push_str(", world!");
    println!("{}", s);

    let s2 = s;
    println!("{}", s2);
    // println!("{}", s);

    let t = String::from("hello");
    takes_ownership(t);
    // println!("{}", t);
    let y = 5;
    makes_copy(y);
    println!("{}", y);

    let s4 = String::from("hello");
    let len = calculate_length(&s4);
    println!("The length of '{}' is {}.", s4, len);

    // let s5 = String::from("hello");
    // change(&s5);

    let mn = String::from("hello world");
    let word = first_word(&mn);
    // mn.clear();
    println!("The first word is: {}", word);

    // let width1 = 30;
    // let height1 = 50;

    let rect1 = Rectangle {
        width: 30,
        height: 50,
    };
    dbg!(&rect1);
    // println!("rect1 is {:#?}", rect1);
    // println!(
    //     "The area of the rectangle is {} square pixels.",
    //     area(&rect1)
    // );
    println!(
        "The area of the rectangle is {} square pixels.",
        rect1.area()
    );

    let rect2 = Rectangle::square(3);
    println!(
        "The area of the rectangle is {} square pixels.",
        rect2.area()
    );
}

fn another_function(a: i32, char: char) -> i32 {
    println!("Another function.");
    println!("The value of a is: {}", a);
    println!("The value of char is: {}", char);
    5
}

fn fibonacci_function(n: i32) -> i32 {
    if n == 0 {
        return 0;
    } else if n == 1 {
        return 1;
    } else {
        return fibonacci_function(n - 1) + fibonacci_function(n - 2);
    }
}

fn celsius_to_fahrenheit(celsius: f64) -> f64 {
    celsius * 1.8 + 32.0
}

fn fahrenheit_to_celsius(fahrenheit: f64) -> f64 {
    (fahrenheit - 32.0) / 1.8
}

fn takes_ownership(some_string: String) {
    // some_string 进入作用域
    println!("{some_string}");
} // 这里，some_string 移出作用域并调用 `drop` 方法。
  // 占用的内存被释放

fn makes_copy(some_integer: i32) {
    // some_integer 进入作用域
    println!("{some_integer}");
} // 这里，some_integer 移出作用域。没有特殊之处

fn calculate_length(s: &String) -> usize {
    s.len()
}

// fn change(some_string: &String) {
//     some_string.push_str(", world");
// }

fn first_word(s: &String) -> &str {
    let bytes = s.as_bytes();

    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[..i];
        }
    }

    &s[..]
}

// fn area(width: u32, height: u32) -> u32 {
//     width * height
// }

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn area(&self) -> u32 {
        self.width * self.height
    }
}

impl Rectangle {
    fn square(size: u32) -> Rectangle {
        Rectangle {
            width: size,
            height: size,
        }
    }
}