fn main() {

    if 3 > 4 { println!{">"}; }

    else { println!{"<"}; }

    let mut zvar = if 2 > 5 {2} else {5};  // 相当于多目运算，各目数据类型必须完全相同

    while zvar > 0 {

        println!("zvar: {}", zvar);

        zvar -= 1;

    }

    for zelement in [1, 2, 3].iter() {

        println!("{}", zelement);

    }

    loop {

        println!("Hello World!");

        break;

    }

}

struct _IpAddr {

    ip_addr: String,

}

impl _IpAddr {

    fn print(&self) {

        println!("{}", self.ip_addr);

    }

}

fn main() {

    let _ip_addr = _IpAddr {ip_addr: String::from("::1")};

    let _id = ;

    match _id {

         => _ip_addr.print(),

        _ => {

              println!("nothing...");

          },

    }

    println!("Hello, world!");

}