Function double

Source Code/09-32.rs:4–10

(a: &mut [i32; 10])

[10, -8, 18, 0, -14, -2, 6, 10, 6, 2]*/
fn main() {
    fn double(a: &mut [i32; 10]) {
        use std::ops::IndexMut;
        use std::ops::MulAssign;
        for n in 0..10 {
            (*(*a).index_mut(n)).mul_assign(2);
        }
    }
    let mut arr = [5, -4, 9, 0, -7, -1, 3, 5, 3, 1];
    double(&mut arr);
    print!("{:?}", arr);