main.rs

struct TicTacToe {
    board: [char; 9],
}

fn display(board: TicTacToe) {
    for row in 0..3 {
        println!(
            " {} | {} | {}",
            board.board[row * 3],
            board.board[row * 3 + 1],
            board.board[row * 3 + 2]
        );
    }
}

fn main() {
    let board = TicTacToe { board: ['.'; 9] };

    display(board);
}