private void computer_make_move()
        {
            //priority 1:  get tick tac toe
            //priority 2:  block x tic tac toe
            //priority 3:  go for corner space
            //priority 4:  pick open space

            Button move = null;

            //look for tic tac toe opportunities
            move = look_for_win_or_block("O"); //look for win
            if (move == null)
            {
                move = look_for_win_or_block("X"); //look for block
                if (move == null)
                {
                    move = look_for_corner();
                    if (move == null)
                    {
                        move = look_for_open_space();
                    }//end if
                }//end if
            }//end if

            move.PerformClick();
        }

        private Button look_for_open_space()
        {
            Console.WriteLine("Looking for open space");
            Button b = null;
            foreach (Control c in Controls)
            {
                b = c as Button;
                if (b != null)
                {
                    if (b.Text == "")
                        return b;
                }//end if
            }//end if

            return null;
        }

        private Button look_for_corner()
        {
            Console.WriteLine("Looking for corner");
            if (A1.Text == "O")
            {
                if (A3.Text == "")
                    return A3;
                if (C3.Text == "")
                    return C3;
                if (C1.Text == "")
                    return C1;
            }

            if (A3.Text == "O")
            {
                if (A1.Text == "")
                    return A1;
                if (C3.Text == "")
                    return C3;
                if (C1.Text == "")
                    return C1;
            }

            if (C3.Text == "O")
            {
                if (A1.Text == "")
                    return A3;
                if (A3.Text == "")
                    return A3;
                if (C1.Text == "")
                    return C1;
            }

            if (C1.Text == "O")
            {
                if (A1.Text == "")
                    return A3;
                if (A3.Text == "")
                    return A3;
                if (C3.Text == "")
                    return C3;
            }

            if (A1.Text == "")
                return A1;
            if (A3.Text == "")
                return A3;
            if (C1.Text == "")
                return C1;
            if (C3.Text == "")
                return C3;

            return null;
        }

        private Button look_for_win_or_block(string mark)
        {
            Console.WriteLine("Looking for win or block:  " + mark);
            //HORIZONTAL TESTS
            if ((A1.Text == mark) && (A2.Text == mark) && (A3.Text == ""))
                return A3;
            if ((A2.Text == mark) && (A3.Text == mark) && (A1.Text == ""))
                return A1;
            if ((A1.Text == mark) && (A3.Text == mark) && (A2.Text == ""))
                return A2;

            if ((B1.Text == mark) && (B2.Text == mark) && (B3.Text == ""))
                return B3;
            if ((B2.Text == mark) && (B3.Text == mark) && (B1.Text == ""))
                return B1;
            if ((B1.Text == mark) && (B3.Text == mark) && (B2.Text == ""))
                return B2;

            if ((C1.Text == mark) && (C2.Text == mark) && (C3.Text == ""))
                return C3;
            if ((C2.Text == mark) && (C3.Text == mark) && (C1.Text == ""))
                return C1;
            if ((C1.Text == mark) && (C3.Text == mark) && (C2.Text == ""))
                return C2;

            //VERTICAL TESTS
            if ((A1.Text == mark) && (B1.Text == mark) && (C1.Text == ""))
                return C1;
            if ((B1.Text == mark) && (C1.Text == mark) && (A1.Text == ""))
                return A1;
            if ((A1.Text == mark) && (C1.Text == mark) && (B1.Text == ""))
                return B1;

            if ((A2.Text == mark) && (B2.Text == mark) && (C2.Text == ""))
                return C2;
            if ((B2.Text == mark) && (C2.Text == mark) && (A2.Text == ""))
                return A2;
            if ((A2.Text == mark) && (C2.Text == mark) && (B2.Text == ""))
                return B2;

            if ((A3.Text == mark) && (B3.Text == mark) && (C3.Text == ""))
                return C3;
            if ((B3.Text == mark) && (C3.Text == mark) && (A3.Text == ""))
                return A3;
            if ((A3.Text == mark) && (C3.Text == mark) && (B3.Text == ""))
                return B3;

            //DIAGONAL TESTS
            if ((A1.Text == mark) && (B2.Text == mark) && (C3.Text == ""))
                return C3;
            if ((B2.Text == mark) && (C3.Text == mark) && (A1.Text == ""))
                return A1;
            if ((A1.Text == mark) && (C3.Text == mark) && (B2.Text == ""))
                return B2;

            if ((A3.Text == mark) && (B2.Text == mark) && (C1.Text == ""))
                return C1;
            if ((B2.Text == mark) && (C1.Text == mark) && (A3.Text == ""))
                return A3;
            if ((A3.Text == mark) && (C1.Text == mark) && (B2.Text == ""))
                return B2;

            return null;
        }