实例1

fn main() {
    println!("Hello, world!");
    let a = 10;
    let b: i32 = 20;

    let mut c = 30i32;
    let d = 30_i32;
    let e = add(add(a, b), add(c, d));

    println!("(a+b) + (c+d) = {}", e);
}

fn add(i: i32, j: i32) -> i32 {
    i + j
}