        private void button1_Click(object sender, EventArgs e)
        {
            DerivedClass d = new DerivedClass();
            BaseClass c = new BaseClass();
            label1.Text = d.display();
            label1.Text += "\n" + c.display();
            label1.Text += "\n" + d.show();
            label1.Text += "\n" + c.show();
            //polymorphism
            c = d;
            label1.Text += "\nPolymorphism :" + c.show();
            //nonpolymorphism
            label1.Text += "\nNon polymorphism :" + c.display();
        }
