Understanding Classes and Objects in Object-Oriented System Design Using C++(lecture-3)

Introduction

Object-Oriented Programming (OOP) is a paradigm that has revolutionized software development by organizing code around real-world entities. At the core of this paradigm lie two fundamental concepts: classes and objects. These concepts form the building blocks of Object-Oriented System Design (OOSD) and are crucial for writing efficient, reusable, and modular code in C++.

In this blog, we’ll explore what classes and objects are, how they relate to each other, and how to implement them in C++.

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What is a Class?

A class in C++ is a user-defined data type that serves as a blueprint for creating objects. It encapsulates data (attributes) and functions (methods) that operate on the data, allowing for data abstraction, encapsulation, and modularity.

In simpler terms, a class defines a type, much like int or float, but the difference is that it can hold both data and operations that manipulate that data.

Syntax of a Class in C++

cppCopy codeclass ClassName {
  // Access Specifiers: public, private, protected
  public: 
    // Attributes (Data members)
    int attribute1;
    double attribute2;

    // Methods (Member functions)
    void method1() {
      // Method definition
    }
};

Here, ClassName is the name of the class, attribute1 and attribute2 are data members, and method1() is a member function. The class itself doesn’t allocate memory for its data members; this happens when an object is created.

Access Specifiers

• Public: Members declared under public can be accessed from anywhere outside the class.
• Private: Members declared under private can only be accessed within the class itself.
• Protected: Similar to private, but also accessible in derived classes.

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What is an Object?

An object is an instance of a class. When a class is defined, no memory is allocated until an object of that class is created. The object is a real-world entity that occupies memory and contains data as defined by the class.

In other words, if a class is a blueprint, then an object is the actual building constructed using that blueprint.

Creating an Object in C++

cppCopy codeClassName objectName;

Here, objectName is an instance of ClassName, and now memory is allocated for the data members of this object.

Example: Class and Object in C++

Let’s illustrate this with a simple example where we define a class Car and create objects of this class.

cppCopy code#include <iostream>
using namespace std;

class Car {
  public:
    // Attributes
    string brand;
    string model;
    int year;

    // Method to display car details
    void displayDetails() {
      cout << "Brand: " << brand << endl;
      cout << "Model: " << model << endl;
      cout << "Year: " << year << endl;
    }
};

int main() {
  // Creating an object of the class Car
  Car car1;

  // Assigning values to the object's attributes
  car1.brand = "Toyota";
  car1.model = "Camry";
  car1.year = 2020;

  // Displaying object details
  car1.displayDetails();

  return 0;
}

Explanation:

• We define a class Car with three attributes: brand, model, and year.
• The class has a method displayDetails() to display the car’s details.
• In the main() function, we create an object car1 of the Car class and assign values to its attributes.
• Finally, we call the displayDetails() method to display the car’s information.

Key Concepts in Classes and Objects

1. Encapsulation: Classes bundle data (attributes) and methods (functions) together, hiding the internal state from the outside world.
2. Abstraction: By using classes, we abstract complex reality by modeling relevant attributes and interactions.
3. Reusability: Once a class is defined, we can create multiple objects (instances) from it, promoting code reuse.
4. Modularity: Classes help organize code into manageable sections that can be developed, tested, and debugged independently.

Conclusion

Classes and objects form the foundation of object-oriented system design, allowing developers to model real-world entities in a structured and intuitive way. By encapsulating data and functionality within classes and creating objects as instances of these classes, C++ developers can build robust and maintainable software systems