What is class and object in C++?

In this chapter of C++ interview questions, we will learn about:

• what is class in c++?
• what is object in c++?
• syntax and example of class and object in c++

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What is Class in C++?

Classes are expanding concepts of structure in C, they can contain data members also contain functions as members.

 

It is a new way of creating and implementing a user-defined data type.

 

Syntax for class:  

Class class-name {

  access_specifier1 member1;
  access_specifier2 member2;

};

access_specifier modify the acess rights for members.

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What is object in c++?

A class provides the blueprints for objects, so basically an object is created from a class.

 

When a program is executed the objects interact by sending messages to one another.

 

Syntax for object: 

If a class name is Rectangle, then two objects of class Rectangle are:

1. Rectangle R1;
2. Rectangle R2;

Similarly we can create any number of objects as per our requirement.

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Example of class and object in c++

In the below example of class and object in c++:

• We have a class named 'Rectangle'
• There are two objects created - R1 and R2
• These objects will use the attributes defined in class like width and length according to their own requirements.

#include<iostream>
using namespace std;

class Rectangle //Class Declaration
{
public:
double width;
double length;
};

int main()
{
Rectangle R1;  //Object1
Rectangle R2;   //Object2
double area;

R1.width=5.0;
R1.length=7.0;
R2.width=10.0;
R2.length=12.0;

area=R1.width*R1.length;
cout<<"Area of Rectangle 1"<<" "<<area<<endl;

area=R2.width*R2.length;
cout<<"Area of Rectangle 2"<<" "<<area<<endl;

Output:

Area of Rectangle 1 35.0

Area of Rectangle 2 120.0

 

As shown above, we can create multiple other objects like R1 and R2 and define their own property i.e. width and length to use for specific purpose.