using System;

namespace SOLID_PRINCIPLES.OCP

{

    public class Invoice

    {

        public virtual double GetInvoiceDiscount(double amount)

        {

            return amount - 10;

        }

    }

    public class FinalInvoice : Invoice

    {

        public override double GetInvoiceDiscount(double amount)

        {

            return base.GetInvoiceDiscount(amount) - 50;

        }

    }

    public class ProposedInvoice : Invoice

    {

        public override double GetInvoiceDiscount(double amount)

        {

            return base.GetInvoiceDiscount(amount) - 40;

        }

    }

    public class RecurringInvoice : Invoice

    {

        public override double GetInvoiceDiscount(double amount)

        {

            return base.GetInvoiceDiscount(amount) - 30;

        }

    }

}

​

namespace SOLID_PRINCIPLES.OCP

{

    class Program

    {

        static void Main(string[] args)

        {

            Invoice FInvoice = new FinalInvoice();

            Invoice PInvoice = new ProposedInvoice();

            Invoice RInvoice = new RecurringInvoice();

​

            double FInvoiceAmount = FInvoice.GetInvoiceDiscount(10000);

            double PInvoiceAmount = PInvoice.GetInvoiceDiscount(10000);

            double RInvoiceAmount = RInvoice.GetInvoiceDiscount(10000);

                Console.WriteLine(FInvoiceAmount);

            Console.WriteLine(PInvoiceAmount);

            Console.WriteLine(RInvoiceAmount);

        }

    }

}