C++ Classes and Objects

Classes: 

Below are some of the features of the classes

• Class is a user-defined data type, it holds its data members as well as member functions that could be accessed and used by creating an instance of that class. 
• The classes are an intrinsic feature of C++ that constitutes Object-Oriented programming. 
• The variables inside a defined class are called data members while the functions are called member functions. 
• Any Class name must begin with an uppercase letter. If a class name is made of more than one word, then the first letter of each word must be in uppercase. 
  Example

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

• Classes contain data members and member functions, however the access of these data members and variable depends on the access specifiers used. 
• Member functions of a class can be defined inside the class definition or outside the class definition. 
• The classes in C++ are similar to structures in C but differ only by; the class defaults to private access control, and the structure defaults to public. 
• All features of Object-Oriented Programming revolve around classes in C++ including Abstraction, Inheritance, Encapsulation, and so on. However, the Objects of the class hold separate copies of data members. During programming, one can create as many objects of a class as needed.

Objects: 

• Every object has its unique data variables. 
• Objects are instances of a class, that holds the data variables declared within a class, and the member functions work on these class objects. 
• Objects are initialized using special class functions known as Constructors. This will be discussed in detail in subsequent tutorials. 
• Additionally, if an object is out of its scope, a special class member function called Destructor is called to release the memory reserved by the object. The C++ language does not have an Automatic Garbage Collector just like JAVA, however, the Destructor in C++ performs this task. 

Box Box1; // Declare Box1 the first object of class Box;
Box Box2; // Declare Box2 the second object of class Box;

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();
}