private void btn_login_Click(object sender, EventArgs e)
        {
            string s = @"Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=Base_Note;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False";

            SqlConnection con = new SqlConnection(s);

            if (con.State == ConnectionState.Closed)
            {
                con.Open();
            }
            string qry1 = "select count(*) from Enseignants where num_Ens = '" + txt_login.Text + "'and nom ='" + txt_pass.Text + "' ";
            string qry2 = "select count(*) from Etudients where num_Etud = '" + txt_login.Text + "'and nom ='" + txt_pass.Text + "' ";

            SqlCommand command1 = new SqlCommand(qry1, con);
            int        result1  = Convert.ToInt32(command1.ExecuteScalar());
            SqlCommand command2 = new SqlCommand(qry2, con);
            int        result2  = Convert.ToInt32(command2.ExecuteScalar());

            if (result1 > 0)
            {
                form_Main_Prof frm = new form_Main_Prof();
                frm.ShowDialog();
                frm.Close();
                txt_login.Text = "";
                txt_pass.Text  = "";
                txt_login.Focus();
            }
            if (result2 > 0)
            {
                form_etud frm = new form_etud();
                frm.ShowDialog();
                frm.Close();
                txt_login.Text = "";
                txt_pass.Text  = "";
                txt_login.Focus();
            }
            else
            {
                labelerror.Visible = true;
            }
            if (con.State == ConnectionState.Open)
            {
                con.Close();
            }
        }
        private void btn_manage_student_Click(object sender, EventArgs e)
        {
            form_etud frm = new form_etud();

            frm.ShowDialog();
        }