private void button1_Click(object sender, EventArgs e)
        {
            MD5 md5Hasher = MD5.Create();
            byte[] data = md5Hasher.ComputeHash(Encoding.Default.GetBytes(textBox2.Text));
            StringBuilder sBuilder = new StringBuilder();
            for (int i = 0; i < data.Length; i++)
            {
                sBuilder.Append(data[i].ToString("x2"));
            }
            string cs = "data source=localhost; database=login; user id=root; pwd=''";
            MySqlConnection liga = new MySqlConnection(cs);
            string query = "select * from login where user =?u and pass=?p";
            try
            {
                MySqlCommand cmd = new MySqlCommand(query, liga);
                cmd.Parameters.AddWithValue("?u", textBox1.Text);
                cmd.Parameters.AddWithValue("?p", sBuilder);
                liga.Open();
                MySqlDataReader leitor = cmd.ExecuteReader();
                if (leitor.Read())
                {
                    MainMenu mm = new MainMenu();
                    mm.Show();
                    this.Hide();
                }
                else MessageBox.Show(Convert.ToString(sBuilder));
            }
            catch (MySqlException ex)
            {
                MessageBox.Show(ex.Message);
            }

            finally
            {
                liga.Close();
            }
        }