bool DataDraft()
        {
            int[] check = FindData();
            if (check[0] != -1 && check[1] != -1)
            {
                int row = check[0];
                int col = check[1];
                int num = grid[row, col];
                {
                    if (isNoSafe(row, col, num))
                    {
                        MessageBox.Show("Please change number!");
                    }
               	}

            }
            else
            {
                return true;
            }
            return false;
       }

int[] FindData()
        {
	   int[] result = new int[2];
	   for (int row = 0; row < N; row++)
            {
		for (int col = 0; col < N; col++)
                {
                    if (grid[row, col] != 0)
                    {
                        result[0] = row;
                        result[1] = col;
                        return result;
                    }
                }
            }

            result[0] = -1;
            result[1] = -1;
            return result;
        }

bool isNoSafe(int row, int col, int num)
        {
            return CheckInRow(row, num) || CheckInCol(col, num) || CheckInBox(row, col, num);
        }

bool CheckInRow(int row, int num)
        {
            for (int col = 0; col < N; col++)
            {

                if (grid[row, col] == num)
                {
                    return true;
                }
            }
            return false;
        }

bool CheckInCol(int col, int num)
        {

            for (int row = 0; row < N; row++)
            {
                if (grid[row, col] == num)
                {
                    return true;
                }
            }
            return false;
        }

bool CheckInBox(int row, int col, int num)
        {
            row = row - (row % 3);
            col = col - (col % 3);

            for (int r = 0; r < 3; r++)
            {
                for (int c = 0; c < 3; c++)
                {
                    if (grid[r + row, c + col] == num)
                    {
                        return true;
                    }
                }
            }

            return false;
        }

 private void button4_Click(object sender, EventArgs e)
        {
            DataDraft();
        }