while expressions

The while keyword works very similar to other languages:

1. fn main() {
2. let mut x = 10;
3. while x != 1 {
4. x = if x % 2 == 0 {
5. x / 2
6. } else {
7. 3 * x + 1
8. };
9. }
10. println!("Final x: {x}");
11. }