Classes and Objects

Ads by YahooAds.in

What is a Class


There are many definitions of class. Some of the best definition that define class are :

• Class is used to create user defined data type.
• Class is a template that defines the form of an object.
• Class is first level of encapsulation.
• A class is a data type whose variables are objects.

General Syntax or General Form of Class :

A class is created by use of the keyword class. The general form of a simple class declaration
is :

class class-name
{
private :

private data and methods

public :

public data and methods

protected :

public data and methods
};
class class name v1,v2,v3....vn;

The private, protected and public are three keywords used to specify the three levels of
access protection.
A class can contain private as well as public members. By default, all items defined in a class
are private.
We will discuss these access specifier in detail later.

v1,v2,v3...vn are the list of variables or objects.

Note :

Do not assign keywords as variable name.

Object :

Object is an instance of class.

In above syntax v1,v2,v3...vn are the objects of class.

Specifically, a class creates a logical framework that defines a relationship between its members. When you declare a variable of a class, you are creating an object. An object has physical existence and is a specific instance of a class. That is, an object occupies memory space, but a type definition does not.


Example :


#include <iostream.h>
#include <conio.h>

class Account
{
public:

int account_no;

void display()
{
cout<<"Account number is : " << account_no;

}

};

void main()
{
clrscr();

Account acc;

acc.account_no=121;

acc.display();

getch();

}
Output :










Description :

-We have created a class named Account.

-Inside class we have declared a public variable of int type named account_no.

-We also created a public method named display in which we display the account_no.

-In main() we have created a object named 'acc' of class Account.

-acc.account_no=121 :

dot (.) operator is used to assign the value 121 to the variable account_no.

-At last we have called the display mathod again with (.) operator.

We will discuus more of this dot operator in next topic.

Note :

We created the object inside the main() method. We can also create the object outside the
main() method just after the class declaration.

The following way is also correct :

class Account
{
public:

int account_no;

void display()
{
cout<<"Account number is : "<Account acc;
}
};

void main()
{
clrscr();

acc.account_no=121;

acc.display();

getch();

}

Output :

     Prev                                                   NEXT

Ads by YahooAds.in