fn main() {
    // 32-bit signed
    let a: i32 = -42;
    // 8-bit unsigned
    let b: u8 = 255;
    // underscores aid reading
    let c: i64 = 9_000_000_000;
    // pointer-sized (indexing)
    let d: usize = 10;
    println!("{a} {b} {c} {d}");
}

signed, unsigned, and sized integers