private void BackBTN_Click(object sender, RoutedEventArgs e)
        {
            StudentControls stud = new StudentControls();

            stud.Show();
            this.Close();
        }
        private void loginButton_Click(object sender, RoutedEventArgs e)
        {
            if (string.IsNullOrEmpty(idTextBox.Text) || string.IsNullOrEmpty(Password_txt.Password))
            {
                MessageBox.Show("Please enter a valid username and password.");
            }
            else
            {
                if (WelcomePage.AllStudentsDictionary.ContainsKey(idTextBox.Text))
                {
                    if (WelcomePage.AllStudentsDictionary[idTextBox.Text].Password == Password_txt.Password)
                    {
                        MessageBox.Show("Logging in..");
                        WelcomePage.StudentLogedIn  = true;
                        WelcomePage.StudentId       = idTextBox.Text;
                        WelcomePage.StudentPassword = Password_txt.Password;

                        StudentControls StudControls = new StudentControls();
                        StudControls.Show();
                        this.Close();
                    }
                    else
                    {
                        MessageBox.Show("Wrong password.");
                    }
                }
                else
                {
                    MessageBox.Show("User does not exist.");
                }
            }
        }