Inheritance in C# – A Practical Guide with Example

What is Inheritance?
In C#, inheritance allows a derived class to access the properties and methods of a base class. It enables code reuse, extension, and customization.

Key Concepts
•Single Inheritance: In C#, Multiple inheritance is not possible, a class can inherit only from one base class.
• Access Levels: Child classes can access public and protected members of the parent class.
• Method Overriding: Derived classes can override base class methods to change the base class method behaviour.
• Syntax: Use the : symbol to inherit from a base class.

Example: Account and SavingsAccount
Base Class

public class Account
{
    public string AccountNumber { get; set; }
    public double Balance { get; set; }
    public void Deposit(double amount)
    {
        Balance += amount;
        Console.WriteLine($"Deposited {amount}. New Balance: {Balance}");
    }
    public void Withdraw(double amount)
    {
        if (Balance >= amount)
        {
            Balance -= amount;
            Console.WriteLine($"Withdrawn {amount}. Remaining Balance: {Balance}");
        }
        else
        {
            Console.WriteLine("Insufficient funds.");
        }
    }
}

Derived Class

public class SavingsAccount : Account
{
    public double InterestRate { get; set; }
    public void ApplyInterest()
    {
        double interest = Balance * InterestRate / 100;
        Balance += interest;
        Console.WriteLine($"Interest applied: {interest}. New Balance: {Balance}");
    }
}

Program Execution

class Program
{
    static void Main(string[] args)
    {
        SavingsAccount savings = new SavingsAccount();
        savings.AccountNumber = "SA12345";
        savings.Balance = 1000;
        savings.InterestRate = 5;

        savings.Deposit(500);
        savings.Withdraw(200);
        savings.ApplyInterest();
    }
}

Output
Deposited 500. New Balance: 1500
Withdrawn 200. Remaining Balance: 1300
Interest applied: 65. New Balance: 1365

Why To Use Inheritance?
• Code Reuse: Common operations like Deposit and Withdraw are defined once in Account.
• Extensibility: SavingsAccount adds new features (like interest calculation) without rewriting everything.
• Cleaner Architecture: Helps organize related classes in a logical structure.

Points to Remember
• Constructors are not inherited but can be called using base().
• Private members of a base class are not accessible in the derived class.
• You can override virtual methods to customize behaviour.
• Sealed classes cannot be inherited.

Advanced Example: Method Overriding
Suppose we want a specialized Withdraw behaviour for SavingsAccount:

public class Account
{
    public virtual void Withdraw(double amount)
    {
        Console.WriteLine($"Withdrawing {amount} from Account.");
    }
}

public class SavingsAccount : Account
{
    public override void Withdraw(double amount)
    {
        Console.WriteLine($"Withdrawing {amount} from SavingsAccount with extra checks.");
    }
}

Now, calling Withdraw() on a SavingsAccount will execute the overridden method.

Conclusion
Inheritance is a fundamental principle of Object-Oriented Programming in C#. By enabling the reuse and extension of base class functionality, it promotes the development of clean, maintainable, and scalable applications. A strong grasp of inheritance concepts significantly enhances your ability to design robust and efficient software within the .NET ecosystem.