private void btn_changepassword_Click(object sender, EventArgs e)
 {
     try
     {
         if (pb_oldpassword_correct.Visible == true && pb_newpassword_correct.Visible == true && pb_newpasswordcheck_correct.Visible == true)
         {
             SqlConnection con = new SqlConnection(SqlLink.linkmethod());
             SqlCommand    cmd = new SqlCommand(SqlUpdate.ChangePasswordmethod(), con);
             cmd.Parameters.AddWithValue("@username", Account);
             cmd.Parameters.AddWithValue("@password", tb_newpassword.Text);
             con.Open();
             SqlDataAdapter adapt = new SqlDataAdapter(cmd);
             DataSet        ds    = new DataSet();
             adapt.Fill(ds);
             con.Close();
             MessageBox.Show("修改成功。");
             this.Close();
         }
     }
     catch (Exception ex)
     {
         MessageBox.Show(ex.Message);
     }
 }