private void btn_Modify_Click(object sender, EventArgs e)
        {
            Global.umode = "MODIFY";
            studentdetails stud_det = new studentdetails();

            stud_det.Show();
        }
        private void btn_Add_Click(object sender, EventArgs e)
        {
            Global.umode = "ADD";
            studentdetails stud_det = new studentdetails();

            stud_det.Show();
        }