Console menu

    char sel = ' ';
    char sub_sel = '0';


    while (sel != 'q' && sel != 'Q')
    {
        Console.Clear();
        Console.WriteLine(">> Main menu <<\n");
        Console.WriteLine("[1] Menu selection");
        Console.WriteLine("[2] Menu selection");
        Console.WriteLine("[3] Menu selection");

        sel = Console.ReadKey().KeyChar;

        // Main menu selections
        if (sel == '1')
        {
            subsel = Console.ReadKey().KeyChar;
        }
        else if (sel == '2')
        {
            subsel = Console.ReadKey().KeyChar;
        }
        else if (sel == '3')
        {
            subsel = Console.ReadKey().KeyChar;
        }

        // Sub menu selections
        while (subsel != '0')
        {
            Console.Clear();
            Console.WriteLine(">> Sub menu <<\n");
            Console.WriteLine("[1] Sub selection");
            Console.WriteLine("[2] Sub selection");
            Console.WriteLine("[3] Sub selection");

            if (subsel == '1')
            {
                Console.ReadKey();
            }
            else if (sel == '2')
            {
                Console.ReadKey();
            }
            else if (sel == '3')
            {
                Console.ReadKey();
            }
        }
    }