A Fundamental Shift in Thinking

Object-Oriented Programming (OOP) is a style of programming where you group related data and functions into a single unit called an Object.

1. The Class (The Blueprint)

A class is like a blueprint for a house. It isn't a house itself; it just describes what a house should have (walls, roof, windows).

class Rectangle {
  public: // Everyone can see this
    int length;
    int width;

    int getArea() {
        return length * width;
    }
};

2. The Object (The Instance)

An object is a specific house built from that blueprint.

Rectangle r1; // Created an object
r1.length = 10;
r1.width = 5;
cout << r1.getArea(); // Result: 50

The Four Pillars of OOP

1. Encapsulation: Hiding the internal data and only showing simple "buttons" to the outside world.
2. Abstraction: Hiding complex details and showing only the essentials.
3. Inheritance: Creating a new class based on an existing one.
4. Polymorphism: Allowing one interface to be used for different types of objects.

Access Modifiers: The Security Guards

• public: Anyone can access these members.
• private: Only the class itself can see these. (This is the default!).
• protected: Only the class and its "children" can see these.

In C++, the only difference between a struct and a class is that a struct's members are public by default, while a class's members are private by default.