C# Programming Tutorial: From Fundamentals to Advanced Application Development

📘 Chapter 4: Object-Oriented Programming in C#

🧠 Introduction

C# is fundamentally an object-oriented programming (OOP) language. OOP is a paradigm that organizes software design around objects, rather than functions and logic. These objects represent real-world entities with attributes (properties) and behaviors (methods).

OOP helps in code reuse, abstraction, modularity, scalability, and maintainability. This chapter explores all the major principles of OOP in C# and how to implement them.

🎯 Four Pillars of OOP in C#

🔧 1. Classes and Objects

🔹 What is a Class?

A class is a blueprint for creating objects. It defines fields, properties, methods, and constructors.

class Car

{

    public string Brand;

    public void Honk()

    {

        Console.WriteLine("Beep!");

    }

}

🔹 What is an Object?

An object is an instance of a class.

Car myCar = new Car();

myCar.Brand = "Toyota";

myCar.Honk();  // Output: Beep!

📋 Class vs Object

📦 2. Encapsulation

Encapsulation refers to wrapping data (fields) and code (methods) into a single unit (class) and restricting access using access modifiers.

🔹 Access Modifiers

✅ Example:

class Person

{

    private int age;

    public void SetAge(int value)

    {

        if (value > 0) age = value;

    }

    public int GetAge()

    {

        return age;

    }

}

🧱 3. Constructors and Destructors

🔹 Constructor

A constructor is a special method that runs automatically when an object is created.

class Student

{

    public string Name;

    public Student(string name)

    {

        Name = name;

    }

}

🔹 Default Constructor

public Student()

{

    Name = "Unknown";

}

🔹 Destructor

~Student()

{

    // Cleanup code

}

Destructors are rarely used directly and are called by the garbage collector.

🧱 4. Inheritance

Inheritance allows one class (child/derived) to inherit fields and methods from another (parent/base).

class Animal

{

    public void Eat() { Console.WriteLine("Eating..."); }

}

class Dog : Animal

{

    public void Bark() { Console.WriteLine("Barking..."); }

}

✅ Usage

Dog d = new Dog();

d.Eat();   // inherited

d.Bark();  // own method

📋 Inheritance Types in C#

🧠 5. Polymorphism

Polymorphism means many forms—the same method behaves differently depending on the object.

🔹 Compile-Time (Method Overloading)

class Calculator

{

    public int Add(int a, int b) => a + b;

    public float Add(float a, float b) => a + b;

}

🔹 Run-Time (Method Overriding)

class Animal

{

    public virtual void Speak() => Console.WriteLine("Animal Sound");

}

class Dog : Animal

{

    public override void Speak() => Console.WriteLine("Bark");

}

Animal a = new Dog();

a.Speak();  // Output: Bark

📋 Table: Overloading vs Overriding

🔗 6. Abstraction

Abstraction is hiding complex implementation and showing only relevant information.

Implemented via:

• Abstract classes
• Interfaces

🔹 Abstract Class

abstract class Shape

{

    public abstract void Draw();

}

class Circle : Shape

{

    public override void Draw()

    {

        Console.WriteLine("Drawing Circle");

    }

}

🔹 Interface

An interface is a pure abstraction—no implementation.

interface IDriveable

{

    void Drive();

}

class Car : IDriveable

{

    public void Drive()

    {

        Console.WriteLine("Driving...");

    }

}

📋 Abstract Class vs Interface

🔄 7. Properties in C#

Properties wrap fields with get and set accessors.

class Product

{

    private int price;

    public int Price

    {

        get { return price; }

        set { if (value > 0) price = value; }

    }

}

Or, use auto-implemented properties:

public string Name { get; set; }

🧪 Sample Program: OOP Principles in Action

using System;

abstract class Animal

{

    public abstract void MakeSound();

}

class Dog : Animal

{

    public override void MakeSound() => Console.WriteLine("Bark");

}

class Program

{

    static void Main()

    {

        Animal myDog = new Dog();

        myDog.MakeSound();  // Output: Bark

    }

}

✅ Summary Table