Arrays and for Loops

We saw that an array can be declared like this:

#![allow(unused)]
fn main() {
let array = [10, 20, 30];
}

You can print such an array by asking for its debug representation with {:?}:

fn main() {
    let array = [10, 20, 30];
    println!("array: {array:?}");
}

Rust lets you iterate over things like arrays and ranges using the for keyword:

fn main() {
    let array = [10, 20, 30];
    print!("Iterating over array:");
    for n in array {
        print!(" {n}");
    }
    println!();
    print!("Iterating over range:");
    for i in 0..3 {
        print!(" {}", array[i]);
    }
    println!();
}

Use the above to write a function pretty_print which pretty-print a matrix and a function transpose which will transpose a matrix (turn rows into columns):

Hard-code both functions to operate on 3 × 3 matrices.

Copy the code below to https://play.rust-lang.org/ and implement the functions:

// TODO: remove this when you're done with your implementation.
#![allow(unused_variables, dead_code)]
fn transpose(matrix: [[i32; 3]; 3]) -> [[i32; 3]; 3] {
    unimplemented!()
}
fn pretty_print(matrix: &[[i32; 3]; 3]) {
    unimplemented!()
}
fn main() {
    let matrix = [
        [101, 102, 103], // <-- the comment makes rustfmt add a newline
        [201, 202, 203],
        [301, 302, 303],
    ];
    println!("matrix:");
    pretty_print(&matrix);
    let transposed = transpose(matrix);
    println!("transposed:");
    pretty_print(&transposed);
}

Bonus Question

Could you use &[i32] slices instead of hard-coded 3 × 3 matrices for your argument and return types? Something like &[&[i32]] for a two-dimensional slice-of-slices. Why or why not?

See the ndarray crate for a production quality implementation.

The solution and the answer to the bonus section are available in the Solution section.