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4.2) Classes and Objects in C++

Classes and Objects are fundamental concepts in object-oriented programming (OOP) that allow you to create structured and modular code by modeling real-world entities as classes and creating instances of those classes as objects. Let’s delve into the details with code examples and explanations:

1. Class Definition


A class is a blueprint that defines the structure and behavior of objects. It contains attributes (data members) and methods (functions) that describe the characteristics and actions of the objects.

#include <iostream>
#include <string>

// Class definition
class Person {
public:
    // Attributes
    std::string name;
    int age;

    // Method to display information
    void displayInfo() {
        std::cout << "Name: " << name << ", Age: " << age << std::endl;
    }
};

2. Creating Objects


An object is an instance of a class. It encapsulates data (attributes) and can perform actions (methods) defined in the class.

int main() {
    // Creating objects of the class
    Person person1;
    Person person2;

    // Assigning values to attributes
    person1.name = "Alice";
    person1.age = 25;

    person2.name = "Bob";
    person2.age = 30;

    // Calling methods on objects
    person1.displayInfo();
    person2.displayInfo();

    return 0;
}

Output:

Name: Alice, Age: 25
Name: Bob, Age: 30

3. Access Control


C++ supports three access control modifiers: public, private, and protected.

By default, members are private.

class Student {
public:
    std::string name;  // Public attribute
    int age;           // Public attribute

private:
    int rollNumber;    // Private attribute

protected:
    double gpa;        // Protected attribute
};

4. Constructors and Destructors


Constructors are special methods that initialize object attributes when an object is created. Destructors are used to clean up resources when an object is destroyed.

class Book {
public:
    std::string title;
    std::string author;

    // Constructor
    Book(std::string t, std::string a) : title(t), author(a) {
        std::cout << "Book created: " << title << " by " << author << std::endl;
    }

    // Destructor
    ~Book() {
        std::cout << "Book destroyed: " << title << std::endl;
    }
};

5. Using Constructors


Constructors can have parameters to initialize attributes during object creation.

int main() {
    Book book1("The Great Gatsby", "F. Scott Fitzgerald");
    Book book2("To Kill a Mockingbird", "Harper Lee");

    return 0;
}

Output:

Book created: The Great Gatsby by F. Scott Fitzgerald
Book created: To Kill a Mockingbird by Harper Lee
Book destroyed: To Kill a Mockingbird
Book destroyed: The Great Gatsby

6. Member Functions


Member functions (methods) are functions defined within a class. They operate on the attributes of the class and can perform various actions.

class Calculator {
public:
    // Member function to add two numbers
    int add(int a, int b) {
        return a + b;
    }
};

Using Member Functions:
You can call member functions on objects to perform actions.

int main() {
    Calculator calculator;

    int result = calculator.add(5, 3);
    std::cout << "Result: " << result << std::endl;

    return 0;
}

Output:

Result: 8

Classes and objects provide a structured way to model and manipulate data in your programs. They promote encapsulation and allow you to design more organized and maintainable code. By defining classes, you create a blueprint for creating objects with well-defined attributes and behaviors.

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