rust

// 不可变变量
 let  guess = String::new();

// 不可变变量可以用let 关键字来遮蔽变量
let x = 5;
let x = x + 1;


// 可变变量
 let mut guess = String::new();

// 数值类型
8 位	i8	u8
16 位	i16	u16
32 位	i32	u32
64 位	i64	u64
128 位	i128	u128
arch	isize	usize

// 浮点
f64   f32

// bool类型
fn main() {
    let t = true;
    let f: bool = false; // with explicit type annotation
}

// 复合类型
// 元组
let tup: (i32, f64, u8) = (500, 6.4, 1);

// 数组
let a = [1, 2, 3, 4, 5];

// 设置数组类型
let a: [i32; 5] = [1, 2, 3, 4, 5];

// 基本函数
fn main() {
    println!("Hello, world!");

    another_function();
}

fn another_function() {
    println!("Another function.");
}


// 带参函数
fn print_labeled_measurement(value: i32, unit_label: char) {
    println!("The measurement is: {}{}", value, unit_label);
}

// 带返回值的函数
fn plus_one(x: i32) -> i32 {
    x + 1
}

// if
fn main() {
    let number = 3;

    if number < 5 {
        println!("condition was true");
    } else {
        println!("condition was false");
    }
}

fn main() {
    let number = 3;

    if number != 0 {
        println!("number was something other than zero");
    }
}

// if-else 
fn main() {
    let number = 6;

    if number % 4 == 0 {
        println!("number is divisible by 4");
    } else if number % 3 == 0 {
        println!("number is divisible by 3");
    } else if number % 2 == 0 {
        println!("number is divisible by 2");
    } else {
        println!("number is not divisible by 4, 3, or 2");
    }
}


// 三元表达式
let condition = true;
let number = if condition { 5 } else { 6 };


// 循环
fn main() {
    let mut counter = 0;

    let result = loop {
        counter += 1;

        if counter == 10 {
            break counter * 2;
        }
    };

    println!("The result is {}", result);
}



// while
fn main() {
    let mut number = 3;

    while number != 0 {
        println!("{}!", number);

        number -= 1;
    }

    println!("LIFTOFF!!!");
}

// for
fn main() {
    let a = [10, 20, 30, 40, 50];
    for element in a {
        println!("the value is: {}", element);
    }
}

struct User {
    active: bool,
    username: String,
    email: String,
    sign_in_count: u64,
}

fn main() {
    let user1 = User {
        email: String::from("someone@example.com"),
        username: String::from("someusername123"),
        active: true,
        sign_in_count: 1,
    };
}

fn build_user(email: String, username: String) -> User {
    User {
        email: email,
        username: username,
        active: true,
        sign_in_count: 1,
    }
    
    
// 方法
    struct Rectangle {
    width: u32,
    height: u32,
}

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

fn main() {
    let rect1 = Rectangle {
        width: 30,
        height: 50,
    };

    println!(
        "The area of the rectangle is {} square pixels.",
        rect1.area()
    );
}
    
    
// match, 类似switch
fn value_in_cents(coin: Coin) -> u8 {
    match coin {
        Coin::Penny => {
            println!("Lucky penny!");
            1
        }
        Coin::Nickel => 5,
        Coin::Dime => 10,
        Coin::Quarter => 25,
    }
}