if expressions

You use if very similarly to how you would in other languages:

1. fn main() {
2. let mut x = 10;
3. if x % 2 == 0 {
4. x = x / 2;
5. } else {
6. x = 3 * x + 1;
7. }
8. }

In addition, you can use it as an expression. This does the same as above:

1. fn main() {
2. let mut x = 10;
3. x = if x % 2 == 0 {
4. x / 2
5. } else {
6. 3 * x + 1
7. };
8. }

Because if is an expression and must have a particular type, both of its branch blocks must have the same type. Consider showing what happens if you add ; after x / 2 in the second example.