1.
```rust
fn main() {
let v = {
let mut x = 1;
x += 2
};
assert_eq!(v, ());
}
```
x += 2;
x
assert_eq!(v, 3);
2.
let x = 3;
assert!(v == 3);
3.
let s = sum(1 , 2);
assert_eq!(s, 3);
fn sum(x: i32, y: i32) -> i32 {
x + y