22 Jan C++ Classes and Objects

In this lesson, we will understand what is a class and object. With that, we will also see some examples to create classes and objects. In C++, a class is a template for an object, whereas an object is an instance of a class.

What is a Class in C++

C++ is an Object-Oriented Programming Language. It is an extension of the C Programming Language i.e., C with Classes. Consider, a class as a blueprint.

Create a Class

To create a class is to declare in C++. At first, to declare a class, use the class keyword in C++. The class is a reserved word in C++.

Let us now see how to define a class in C++. The public is an access specifier in C++. For the public access specifier, the members can be accessed from outside the class easily. In the below example, the class members are length and width:

class Rectangle {
  public:
    double length;
    double width;
}

What is an Object In C++

An object is an instance of a class i.e., an object is created from a class. Object represents real-life entities, for example, a Bike is an object. Object has State, Behavior, and Identity:

• Identity: Name of Bike
• State (Attributes): The data of object Bike i.e., Color, Model, Weight, etc.
• Behavior (Methods): Behavior of object Bike like to Drive, Brake

Let us now see the representation, with Bike as an object:

Create an Object

An object is a runtime entity with state and behavior. To create an object in C++, we use a Class. The syntax is as follows:

ClassName obj;

Above, we have set the class name with ClassName followed by the object obj. This is how an object is created in C++.

Let us see the above example and create three objects in C++:

// Create objects of class Rectangle

// Declaring rect1, rect2, rect3 of type Rectangle
Rectangle rct1;
Rectangle rct2;
Rectangle rct3;

Example: Classes and Objects

Let us see the complete example to create a class and object. In this example, we will also learn how to access the attributes of the class using the dot:

#include <iostream>
using namespace std;

class Rectangle {

  // Access Specifier
  public:  
   double length; // Attribute1
   double width; // Attribute2
};
 
int main() {
     
     // Creating an object rct
     // Declaring rct of type Rectangle
     Rectangle rct;
     
     double area;
     
     // Accessing attributes 
     // Set the values of length and width
     rct.length = 25;
     rct.width = 20;
     
     cout <<"\nLength of Rectangle = "<<rct.length; 
     cout <<"\nWidth of Rectangle = "<<rct.width; 
     
     // Calculating Area of Rectangle     
     area = rct.length * rct.width;
 
     cout<<"\n\nArea of Rectangle = "<<area;
}

Output

Length of Rectangle = 25
Width of Rectangle = 20

Area of Rectangle = 500

If you liked the tutorial, spread the word and share the link and our website Studyopedia with others.

For Videos, Join Our YouTube Channel: Join Now