What is an example where OCP is violated?

Before (OCP Violation):

public class DiscountCalculator

public decimal CalculateDiscount(string customerType)

if (customerType == "Regular") return 10;

if (customerType == "Premium") return 20;

if (customerType == "VIP") return 30;

return 0;

If you need to support a new customer type, you must modify this method — violating OCP.

After (OCP Compliant):

public interface IDiscountStrategy

decimal GetDiscount();

public class RegularCustomerDiscount : IDiscountStrategy

public decimal GetDiscount() => 10;

public class PremiumCustomerDiscount : IDiscountStrategy

public decimal GetDiscount() => 20;

public class VipCustomerDiscount : IDiscountStrategy

public decimal GetDiscount() => 30;

Now you can add new customer types without modifying existing code — just create a new

strategy.