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根据条件是否为运行某些代码true以及在条件为时重复运行某些代码的能力true是大多数编程语言中的基本构建块

if表达式

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");
    }
}

if在let声明中使用

代码块的计算结果是其中的最后一个表达式，数字本身也是表达式。在这种情况下，整个if表达式的值取决于执行哪个代码块。这意味着有可能从每个臂产生的值if必须是相同的类型

fn main() {
    let condition = true;
    let number = if condition { 5 } else { 6 };

    println!("The value of number is: {number}");
}

循环重复(loop、while、for)

• 可以使用break跳出循环，continue跳过本次循环进入下一次循环

重复代码loop

死循环(直接EMO)

fn main() {
    loop {
        println!("again!");
    }
}

从循环返回值

break用于停止循环的表达式之后添加想要返回的值(好像return表达式)

fn main() {
    let mut counter = 0;

    let result = loop {
        counter += 1;

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

    println!("The result is {result}"); // 20
}

消除多个循环之间歧义的循环标签

循环标签必须以单引号开头(反人类🤔)

fn main() {
    let mut count = 0;
    'counting_up: loop {
        println!("count = {count}");
        let mut remaining = 10;

        '_inner: loop {
            println!("remaining = {remaining}");
            if remaining == 9 {
                break;
            }
            if count == 2 {
                break 'counting_up;
            }
            remaining -= 1;
        }

        count += 1;
    }
    println!("End count = {count}");
}

条件循环while

fn main() {
    let mut number = 3;

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

        number -= 1;
    }

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

循环遍历集合for

fn main() {
    let a = [10, 20, 30, 40, 50];

    for element in a {
        println!("the value is: {element}");
    }
}

fn main() {
    for number in (1..=4).rev() {
        println!("{number}!");
    }
    println!("LIFTOFF!!!");
    for number in (1..4).rev() {
        println!("{number}!");
    }
    println!("LIFTOFF!!!");
}