C++ OOP

🧠 C++ OOP (Object-Oriented Programming)

Object-Oriented Programming (OOP) in C++ is a programming paradigm based on the concept of objects that contain data (attributes) and functions (methods).
It helps in writing clean, modular, reusable, and maintainable code.

🔹 1. Core Concepts of OOP in C++

There are four main pillars of OOP:

  1. Class

  2. Object

  3. Encapsulation

  4. Inheritance

  5. Polymorphism

  6. Abstraction

(Usually taught as 4 pillars, but abstraction & encapsulation are often separated.)

🔹 2. Class

A class is a blueprint/template for creating objects.

class Student {
public:
int id;
string name;

void display() {
cout << id << " " << name;
}
};

🔹 3. Object

An object is an instance of a class.

int main() {
Student s1;
s1.id = 101;
s1.name = "Sanjit";
s1.display();
}

🔹 4. Encapsulation

Encapsulation means binding data and methods together and restricting direct access.

class Account {
private:
int balance;

public:
void setBalance(int b) {
balance = b;
}

int getBalance() {
return balance;
}
};

✔ Data is protected
✔ Access through public methods

🔹 5. Abstraction

Abstraction means showing only essential details and hiding implementation.

class Car {
public:
void start() {
cout << "Car started";
}
};

User does not know how the engine starts—only that it starts.

🔹 6. Inheritance

Inheritance allows a class to acquire properties of another class.

class Animal {
public:
void eat() {
cout << "Eating";
}
};

class Dog : public Animal {
public:
void bark() {
cout << "Barking";
}
};

Dog d;
d.eat();
d.bark();

✔ Code reusability
✔ Parent → Child relationship

🔹 7. Polymorphism

Polymorphism means many forms.

Example: Function Overriding

class Animal {
public:
virtual void sound() {
cout << "Animal sound";
}
};

class Dog : public Animal {
public:
void sound() {
cout << "Dog barks";
}
};

Animal* a;
Dog d;
a = &d;
a->sound(); // Dog barks

✔ Achieved using virtual functions

🔹 8. Constructors and Destructors

Constructor

Called automatically when object is created.

class Demo {
public:
Demo() {
cout << "Constructor called";
}
};

Destructor

Called automatically when object is destroyed.

~Demo() {
cout << "Destructor called";
}

🔹 9. Access Specifiers

SpecifierAccess
publicAccessible everywhere
privateOnly inside class
protectedClass + derived classes

🔹 10. OOP vs Procedural Programming

OOPProcedural
Object-basedFunction-based
Better securityLess secure
ReusableLess reusable
Complex projectsSmall programs

📌 Real-Life Example (OOP Thinking)

  • Class → Car

  • Object → BMW, Audi

  • Encapsulation → Engine hidden

  • Inheritance → ElectricCar inherits Car

  • Polymorphism → start() behaves differently

📌 Summary

  • OOP is based on classes and objects

  • Improves reusability, security, maintainability

  • Key pillars: Encapsulation, Abstraction, Inheritance, Polymorphism

  • Core foundation of modern C++ programming

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