C++ Classes and Objects

Classes:

• The classes are the most important feature of C++ that leads to Object Oriented programming.
• Class is a user defined data type, which holds its own data members and member functions, which can be accessed and used by creating instance of that class.
• The variables inside class definition are called as data members and the functions are called member functions.
• Class name must start with an uppercase letter. If class name is made of more than one word, then first letter of each word must be in uppercase. Example,

   

• Classes contain, data members and member functions, and the access of these data members and variable depends on the access specifiers.
• Class's member functions can be defined inside the class definition or outside the class definition.
• Class in C++ are similar to structures in C, the only difference being, class defaults to private access control, where as structure defaults to public.
• All the features of OOPS, revolve around classes in C++. Inheritance, Encapsulation, Abstraction etc.
• Objects of class holds separate copies of data members. We can create as many objects of a class as we need.

Objects:

• Objects are instances of class, which holds the data variables declared in class and the member functions work on these class objects.
• Each object has different data variables.
• Objects are initialised using special class functions calledConstructors. We will study about constructors later.
• And whenever the object is out of its scope, another special class member function called Destructor is called, to release the memory reserved by the object. C++ doesn't have Automatic Garbage Collector like in JAVA, in C++ Destructor performs this task.

Example:

#include <iostream>


class Box
{
public:
double length;   // Length of a box
double breadth;  // Breadth of a box
double height;   // Height of a box
};

void main( )
{
Box Box1;        // Declare Box1 object of class Box
Box Box2;        // Declare Box2 object of class Box

double volume = 0.0;     // Store the volume of a box here
 
// box 1 specification
Box1.height = 5.0; 
Box1.length = 5.0; 
Box1.breadth = 3.0;

// box 2 specification
Box2.height = 10.0;
Box2.length = 5.0;
Box2.breadth = 3.0;

// volume of box 1
volume = Box1.height * Box1.length * Box1.breadth;
cout << "Volume of Box1 : " << volume <<endl;

// volume of box 2
volume = Box2.height * Box2.length * Box2.breadth;
cout << "Volume of Box2 : " << volume <<endl;
   
getch();
}

Output:

Volume of Box1 : 75
Volume of Box2 : 150

• It is important to note that private and protected members can not be accessed directly using direct member access operator (.).
• We will learn how private and protected members can be accessed.

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