learn-Rust 

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use std::collections::HashMap;

fn first_function() {
    println!("hello im a function");
}

fn main() {
    //变量
    let name = "Steve";
    let age = 20;
    println!("hello {} i'm {}", name, age);
    println!("hello world");

    //让变量值可变
    let mut y = 200;
    println!("Before: {}", y);
    y = 150;
    println!("After {}", y);

    // let my_num = 5;
    // let my_double = 5.55;
    // let my_letter = 'D';
    // let my_bool = true;
    // let my_text = "hello";

    //常量 必须指定类型
    // const TEST: i32 = 120;
    // TEST + y;

    let is_bool = true;
    if is_bool {
        println!("That is right");
    } else {
        println!("That is Error")
    }

    let score = 90;
    if score >= 90 {
        println!("Good");
    } else if score >= 80 {
        println!("Normal");
    }

    let day = 4;
    match day {
        1 => println!("Monday"),
        2 => println!("Tuesday"),
        3 => println!("Wednesday"),
        4 => println!("Thursday"),
        5 => println!("Friday"),
        6 => println!("Saturday"),
        7 => println!("Sunday"),
        _ => println!("NaN"), //default
    }

    let mut count = 1;
    loop {
        println!("hello rust");
        if count == 3 {
            break;
        }
        count += 1
    }

    let mut asum = 1;
    while asum <= 5 {
        if asum == 3 {
            asum += 1;
            continue;
        }
        println!("asum {}", asum);
        asum += 1
    }

    for i in 1..6 {
        //不包含6
        println!("i is {}", i);
    }

    for i in 1..=6 {
        //包含6
        println!("i is {}", i)
    } // break终止循环 continue跳过

    first_function();

    let test = "hello".to_string();
    let test2 = String::from("hello");
    println!("length: {}", test.len());
    let tesult = format!("{} {}", test, test2);
    println!("{}", tesult);

    // let arr = ["steve", "alice"];
    let mut arrs = vec![1, 2];
    arrs.push(3);

    let mut capitalcities = HashMap::new();
    capitalcities.insert("Steve", "Alice");
    capitalcities.insert("New York", "Tokyo");
    println!("Capital of Japan is {}", capitalcities["Japan"]);

    enum Test {
        Up,
        Down,
        Left,
        Right,
    }
    let a = Test::Up;
    println!("{}", a)
}

// fn add(a: i32, b: i32) -> i32 {
//     return a + b;
// }

// let sum = add(2, 4);