private void button1_Click(object sender, EventArgs e)
        {
            TeacherViewStudent std = new TeacherViewStudent();

            this.Hide();
            std.Show();
        }
        private void btnUploadDMC_Click(object sender, EventArgs e)
        {
            TeacherViewStudent t = new TeacherViewStudent();

            this.Hide();
            t.Show();
        }