In Rust, `i32` is a signed 32-bit integer type. Rust usually infers `i32` for an integer when you do not specify its type; use an annotation or a literal suffix to choose a type explicitly. section 1.4
fn main() {
let small_number: u8 = 10;
}
An explicit type annotation makes `small_number` an unsigned integer; use `i32` in the annotation to choose that type instead. section 1.4
An i32 return value
The function signature declares an `i32` return type, and its final expression, `8`, supplies the returned value. section 1.6
