Classes and Objects in C++

In C++, classes and objects are the very basic elements that lead to Object-Oriented programming. A class defines the structure and behaviors, while an object is an instance that holds real data in memory. Multiple objects can be created from a single class, each with its own data but sharing the same behaviors.

In real life, you can think of a Student class as a template for students in a school. Each individual student (object) can have their own name, age, and grade.

  • Student class: Defines what properties (name, age, grade etc) each student will have.
  • student1, student2, …. student N are objects of the Student class, representing different students with their own data.

Class in C++

  • A class is like a blueprint or template that defines the properties (data members) and behaviors (member functions) of objects.
  • It is a user-defined data type that outlines what attributes an object of that class will have and what actions it can perform.
  • For example, in a Student class, the class defines properties like name, age, and grade, and actions like study() or takeExam().

Object in C++

  • An object is an instance of a class. When you create an object, it takes on the attributes and behaviors defined by the class.
  • You can think of an object as an actual thing that is created based on the class. It has real values for the properties and can perform the actions specified by the class.
  • For example, a specific student (let’s call it “John”) is an object of the Student class. John’s properties would be his actual name, age, and grade, and his behaviors would include actions like studying or taking an exam.
Important: when an object is created, a constructor is invoked automatically.

Relationship between Class and Object

  • The class defines the structure and behavior, while the object is the actual instance that exists in memory.
  • Objects are created based on the class, and they hold actual data for the properties defined in the class.
  • You can create many objects from a single class, and each object will have its own values for the properties but can share the same behaviors.
Important: What Happens If No Object Is Created?

  • Without creating an object, you can’t interact with the class at all
  • A class does not use any memory on its own until an object is created. The class only exists as a template in the program.

Components of Class

The building block of C++ that leads to Object-Oriented programming is a Class. It contains the following major components

1. Access Specifiers: There are three types of access specifiers that can be used in class which are

  • Public
  • Private
  • Protected

Data variables and functions are defined under any of the access specifiers. If there is no access specifier used in class, then by default it is private.

2. Data variables and functions: Class is a user-defined data type, which holds its own data variables and functions (methods). Functions and variables of a class can be accessed and used by creating an instance of that class (called object).

Simple C++ Program for Class and Objects in OOP

#include <iostream>
#include <string>
using namespace std;class Student {
public:
// Data members
string name;
int age;
char grade;

// Function to display student information
void displayStudentInfo() {
cout << “Name: ” << name << endl;
cout << “Age: ” << age << endl;
cout << “Grade: ” << grade << endl;
}
};

int main() {
// Creating two objects of the Student class
Student student1;
Student student2;

// Assigning values to the first student
student1.name = “John”;
student1.age = 20;
student1.grade = ‘A’;

// Assigning values to the second student
student2.name = “Alice”;
student2.age = 22;
student2.grade = ‘B’;

// Displaying student information for both students
cout << “Student 1 Information: ” << endl;
student1.displayStudentInfo();

cout << “\nStudent 2 Information: ” << endl;
student2.displayStudentInfo();

return 0;
}

 Output:

Student 1 Information:
Name: John
Age: 20
Grade: A

Student 2 Information:
Name: Alice
Age: 22
Grade: B

Advantages of Using Classes In OOP

In C++, using classes and objects provides several benefits, primarily related to object-oriented programming (OOP) principles. Here are the key advantages:

1. Encapsulation

  • Definition: Encapsulation is the concept of bundling the data (variables) and methods (functions) that operate on the data into a single unit, or class.
  • Benefit: This allows you to hide the internal details of the class (data members), exposing only necessary functionality through public methods. This improves security and prevents unintended interference with an object’s internal state.

2. Code Reusability

  • Definition: Once a class is created, it can be reused to create multiple objects of that class.
  • Benefit: This reduces code duplication, saves time, and ensures consistency, as you can reuse the same class to create many instances with similar behavior but different data.

3. Abstraction

  • Definition: Abstraction allows you to hide the complexity of the implementation and expose only the necessary functionality.
  • Benefit: It simplifies interaction with objects, as users only need to know how to use an object, not how it works internally. For example, an object of a class may have a complex internal structure, but users only interact with its public interface (methods).

4. Inheritance

  • Definition: Inheritance allows a class to inherit properties and methods from another class.
  • Benefit: It facilitates the creation of a new class based on an existing class, which promotes code reuse and extension of functionality without modifying existing code. This helps in building a hierarchy of classes, like a parent-child relationship.

5. Polymorphism

  • Definition: Polymorphism allows objects of different classes to be treated as objects of a common base class, typically using function overriding or function overloading.
  • Benefit: This allows you to design flexible and scalable systems where a single function can operate on different types of objects, making the code more maintainable and easier to extend.

6. Modularity

  • Definition: Classes help in organizing code into smaller, self-contained modules, where each class can focus on a specific functionality or concept.
  • Benefit: It makes the codebase easier to maintain, debug, and scale. Modularity promotes a clearer separation of concerns, improving readability and ease of collaboration.

7. Improved Maintainability

  • Definition: By organizing code into classes and objects, maintenance tasks become more manageable.
  • Benefit: When changes are required, they can often be made within a class without affecting other parts of the program, reducing the chances of introducing bugs elsewhere. It also makes it easier to fix bugs or update functionality in isolated components.

8. Data Protection

  • Definition: Classes in C++ allow you to define the access level of each data member (using public, private, and protected).
  • Benefit: This allows you to control how data is accessed and modified. By making data members private and exposing only necessary methods to interact with the data, you can protect the integrity of the object’s state.

9. Better Design and Structuring

  • Definition: OOP principles, especially classes and objects, help in designing systems that mirror real-world concepts, making it easier to structure complex applications.
  • Benefit: A well-designed class structure results in a program that is easier to understand and align with real-world problems, improving both developer productivity and application performance.

10. Dynamic Memory Management (With Constructors and Destructors)

  • Definition: C++ classes can manage dynamic memory allocation and deallocation using constructors and destructors.
  • Benefit: This allows for efficient resource management, such as allocating memory when an object is created and freeing up resources when the object goes out of scope. Proper memory management ensures efficient use of system resources.