fn add_to_vec(v: &mut Vec<i32>) {
    v.push(5);
}

fn display_vec(v: &Vec<i32>) {
    println!("{:?}", v);
}

fn main() {
   let mut v = vec![1,2,3,4];
   let r = &mut v;
   add_to_vec(r);
   println!("{:?}",r);
   display_vec(&v);
}