1. if语句

下面看一个示例：

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");
    }
}

(1) 需要注意的是，RUST与cpp不同，不可以将整型识别为bool，所以下面的语句会报错：

fn main() {
    let number =3;
    if number{
        println!("condition is true");
    }else{
        println!("condition is false");
    }
}

(2)另一个需要注意的点是，if多个分支返回的值要是同类型

fn main() {
    let condition = true;

    let number = if condition { 5 } else { "six" };

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

因为RUST需要在编译的时候确定number的类型，如果类型无法确定后续对代码的保证会降低

2. 循环

2.1 loop

一个简单的例子：

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

比较特别的一个点是，允许循环标签来在内循环中断外部循环

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

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

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

2.2 while

while的用法和其他语言类似，同样需要注意表达式的返回值必须为布尔值

fn main() {
    let mut number = 3;
    while number != 0 {
        println!("{number}!");
        number -= 1;
    }
    println!("LIFTOFF!!!");
}

遍历数组示例：

fn main() {
    test1();
}
fn test1(){
    let a=[1,2,3,4,5];
    let mut index=0;
    while index<5{
        println!("the value of a[{index}] is {} ",a[index]);
        index+=1;
    }
}

2.3 for

for的遍历array的写法很类似于cpp中的for(auto ele:array)

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

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

一个倒计时的例子

fn main() {
    for number in (1..4).rev() {
        println!("{number}!");
    }
    println!("LIFTOFF!!!");
}
//输出结果 3 2 1