fn main() {
    let n = 4;
    for i in 0..n {
        print!("{}", i);  // 0123
    }
    
    let mut range = 0..4;
    loop {
        match range.next() {
            Some(x) => {
                print!("{}", x);   // 0123
            }
            None => { break }
        }
    }

    let v = (1..5).map(|x| x*x).collect::<Vec<u32>>();
    println!("{:?}", v);         // [1, 4, 9, 16]

}