private void instantiateAsSeniorCitizen_Click(object sender, EventArgs e)
        {
            PurchaseForm purchaseForm = new PurchaseForm();

            purchaseForm.Customer = new SeniorCitizen();
            purchaseForm.Activate();
            purchaseForm.Show();
        }
        private void instantiateAsCustomer_Click(object sender, EventArgs e)
        {
            PurchaseForm purchaseForm = new PurchaseForm();

            purchaseForm.Customer = new Customer();
            purchaseForm.Activate();
            purchaseForm.Show();
        }