private void btnProfessor_Click(object sender, EventArgs e)
        {
            this.Hide();
            ProfessorForm professor = new ProfessorForm();

            professor.Show();
        }
        private void btnBack_Click(object sender, EventArgs e)
        {
            this.Hide();
            ProfessorForm nP = new ProfessorForm();

            nP.Show();
        }