int userInput()
{
    int next;
    bool exit = false;

    cout << endl;
    cout << setw(4) << "7" << setw(4) << "8" << setw(4) << "9" << endl;
    cout << setw(4) << "4" << setw(4) << "5" << setw(4) << "6" << endl;
    cout << setw(4) << "1" << setw(4) << "2" << setw(4) << "3" << endl;
    cout << endl;
    cout << "Please enter a digit (0 to abandon): " << endl;
    cin >> next;

    while (exit == false)
    {
        if ((next >= 0) && (next <= 9))
        {
            exit = true;
        }

        else
        {
            cout << endl;
            cout << "Enter a digit between 0 and 9!" << endl;
            cin >> next;
        }
    }

    return next;
}