fn main() {
    // Fall For type 'String', mutable
    let mut s1 = String::from("hello");
    let t1 = &s1;
    println!("t1: the value of variable s1 is {}", t1);
    println!("t1: the stack address of variable s1 is {:p}", &t1);
    let s2 = &mut s1;
    //println!("s1: the value of variable s1 is {}", s1);  // ERROR
    // println!("s1: the stack address of variable s1 is {:p}", &s1);  // ERROR
    println!("s2: the value of variable s2 is {}", s2);
    println!("s2: the stack address of variable s2 is {:p}", &s2);
}