public void  CheckLogin(TextBox Username, TextBox Password)
        {
            SqlCeConnection Connection = DataBaseConnection.Instance.Connection;

            if (Username.TextLength > 0 && Password.TextLength > 0)
            {
                try
                {
                    SqlCeCommand logincommand = new SqlCeCommand(@"SELECT * FROM Users WHERE UserName=@uname and Password=@pass", Connection);
                    logincommand.Parameters.AddWithValue("@uname", Username.Text);
                    logincommand.Parameters.AddWithValue("@pass", Encrypt.hashPassword(Password.Text));
                    SqlCeDataReader loginReader = logincommand.ExecuteReader();

                    if (loginReader.Read() &&
                        loginReader["UserName"].ToString() == Username.Text &&
                        loginReader["Password"].ToString() == Encrypt.hashPassword(Password.Text))
                    {
                        SqlCeCommand admincommand = new SqlCeCommand(@"SELECT * FROM Administration WHERE UsersId =@LoggedId", Connection);
                        admincommand.Parameters.AddWithValue("@LoggedId", loginReader["Id"]);
                        SqlCeDataReader adminReader = admincommand.ExecuteReader();     //ADMIN

                        SqlCeCommand teachercommand = new SqlCeCommand(@"SELECT * FROM Teachers WHERE UsersId =@LoggedId", Connection);
                        teachercommand.Parameters.AddWithValue("@LoggedId", loginReader["Id"]);
                        SqlCeDataReader teacherReader = teachercommand.ExecuteReader();     //TEACHER

                        SqlCeCommand directorcommand = new SqlCeCommand(@"SELECT * FROM Directors WHERE UsersId =@LoggedId", Connection);
                        directorcommand.Parameters.AddWithValue("@LoggedId", loginReader["Id"]);
                        SqlCeDataReader directorReader = directorcommand.ExecuteReader();     //DIRECTOR

                        User user = new User((int)loginReader["Id"], (string)loginReader["UserName"], (string)loginReader["Password"]);

                        if (adminReader.Read() && user.Id == (int)adminReader["UsersId"])
                        {
                            flag = true;
                            Admin admin   = new Admin((int)adminReader["Id"], (string)adminReader["Name"], (string)adminReader["Surname"], (int)adminReader["UsersId"]);
                            Form  newform = new AdministrationForm(user, admin);
                            newform.Show();
                        }
                        else if (teacherReader.Read() && user.Id == (int)teacherReader["UsersId"])
                        {
                            flag = true;
                            Teacher teacher = new Teacher((int)teacherReader["Id"], (string)teacherReader["Name"], (string)teacherReader["Surname"], (string)teacherReader["Address"], (string)teacherReader["Phone_number"], (int)teacherReader["UsersId"]);
                            Form    newform = new TeacherForm(user, teacher);
                            newform.Show();
                        }
                        else if (directorReader.Read() && user.Id == (int)directorReader["UsersId"])
                        {
                            flag = true;
                            Director director = new Director((int)directorReader["Id"], (string)directorReader["Name"], (string)directorReader["Surname"], (int)directorReader["UsersId"]);
                            Form     newform  = new DirectorForm(user, director);
                            newform.Show();
                        }
                        else
                        {
                            flag = false;
                            MessageBox.Show("Netacni podaci");
                        }
                    }
                    else
                    {
                        flag = false;
                        MessageBox.Show("Netacni podaci");
                        Username.Text = "";
                        Password.Text = "";
                    }
                }
                catch (Exception ex)
                {
                    flag = false;
                    MessageBox.Show("Neočekivana greška:" + ex.Message);
                }
            }
        }
        public void  CheckLogin(TextBox Username, TextBox Password)
        {
            LoginForm logf             = new LoginForm();
            string    Dir              = logf.GetHomeDirectory();
            string    connectionString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString + "Data Source ='" + @Dir + "\\DataBase.sdf'";

            using (SqlCeConnection Connection = new SqlCeConnection())
            { if (Username.TextLength > 0 && Password.TextLength > 0)
              {
                  try
                  {
                      Connection.ConnectionString = connectionString;
                      Connection.Open();
                      SqlCeCommand logincommand = new SqlCeCommand(@"SELECT Id,UserName,Password FROM Users
                                        WHERE UserName=@uname and  Password=@pass", Connection);
                      logincommand.Parameters.AddWithValue("@uname", Username.Text);
                      logincommand.Parameters.AddWithValue("@pass", Password.Text);
                      SqlCeDataReader loginReader = logincommand.ExecuteReader();

                      if (loginReader.Read() &&
                          loginReader["UserName"].ToString() == Username.Text &&
                          loginReader["Password"].ToString() == Password.Text)
                      {
                          SqlCeCommand admincommand = new SqlCeCommand(@"SELECT Name,Surname,UsersId FROM Administration
                                                             WHERE UsersId =@LoggedId", Connection);
                          admincommand.Parameters.AddWithValue("@LoggedId", loginReader["Id"]);
                          SqlCeDataReader adminReader = admincommand.ExecuteReader();   //ADMIN

                          SqlCeCommand teachercommand = new SqlCeCommand(@"SELECT Name,Surname,UsersId FROM Teachers
                                                             WHERE UsersId =@LoggedId", Connection);
                          teachercommand.Parameters.AddWithValue("@LoggedId", loginReader["Id"]);
                          SqlCeDataReader teacherReader = teachercommand.ExecuteReader();   //TEACHER

                          SqlCeCommand directorcommand = new SqlCeCommand(@"SELECT Name,Surname,UsersId FROM Directors
                                                             WHERE UsersId =@LoggedId", Connection);
                          directorcommand.Parameters.AddWithValue("@LoggedId", loginReader["Id"]);
                          SqlCeDataReader directorReader = directorcommand.ExecuteReader();   //DIRECTOR

                          if (adminReader.Read() && loginReader["Id"].ToString() == adminReader["UsersId"].ToString())
                          {
                              flag = true;
                              Form newform = new AdministrationForm();
                              newform.Show();
                          }
                          else if (teacherReader.Read() && loginReader["Id"].ToString() == teacherReader["UsersId"].ToString())
                          {
                              flag = true;
                              Form newform = new TeacherForm();
                              newform.Show();
                          }
                          else if (directorReader.Read() && loginReader["Id"].ToString() == directorReader["UsersId"].ToString())
                          {
                              flag = true;
                              Form newform = new DirectorForm();
                              newform.Show();
                          }
                          else
                          {
                              flag = false;
                              MessageBox.Show("Netacni podaci");
                          }
                      }
                      else
                      {
                          flag = false;
                          MessageBox.Show("Netacni podaci");
                          Username.Text = "";
                          Password.Text = "";
                      }
                  }
                  catch (Exception ex)
                  {
                      flag = false;
                      MessageBox.Show("Neočekivana greška:" + ex.Message);
                  }
              }
            }
        }