02. classes and objects

7/31/2019 02. Classes and Objects

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Abdul Wahab [email protected]

University of Science and Technology Bannu

C++ObjectOrientedProgrammingUsing


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Object

Any thing which has some properties and some behaviors.

Object is an instance of a class.


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Class

A class is group of objects having identical properties, common behavior

and shared relationship.

Class: Car

Properties: Company, Model, Color and Capacity etc.

Action: Speed() and Break().

Class: Computer

Properties: Brand, Price, Processor Speed and Ram etc.

Action: Processing(), Display() and Printing().

The entire group of data and code of an object can be built as a user-defined data type using class.


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Access Specifiers

Private:

The private members of a class are accessible only by the memberfunctions or friend functions of the class.

Public:The public members are accessible from any where in the program.

Protected:

The protected members of a class are accessible by the memberfunctions of the class and the classes which are derived from this class.


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General Form of a Class

classclass_name

{

private:

//private data and functions

public:

//public data and function

}object_list;


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Declaring Objects

Defining objects of class is known as class instantiation

When objects are created only during that moment, memory is allocatedto them

intx, y;

charch;

itema, b, *c;


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Properties of Objects

It is individual

It holds data as well as operation method that handles data

Its scope is limited to the block in which it is defined


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Accessing Class Members

Object can access public member variables and functions by usingoperators dot( . ) and arrow ( -> )

[object name] [operator] [member name]

e.g. a.show(); Where a is normal object

b->show(); Where b is pointer object


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Example

classitem

{

int codno;

float price;

int qty;

};

void main()

{

classitem a;

clrscr();

a.codeno=123; // Direct

a.price=150.00; // Access

a.qty=15; // Not allowed

}

Optional


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The Public Keyword

The keyword publiccan be used to allow object to access the membervariables of a class directly

Public is written inside the class terminated by colon. e.g.

class Sample

{

public:

// Public Members

};


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Example

classitem

{

public:

int codno;

float price;int qty;

};

void main()

{

classitem a;

clrscr();

a.codeno=123;a.price=150.00;

a.qty=15;

}


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The Private Keyword

It is used to prevent direct access to members of the class

By default private access specifier is used

Private members can be accessed through the public member function


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Example

void item :: set_show()

{codeno=123;

price=150.00;

qty=15;

cout


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Output

123150.00

15


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The Protected Keyword

Access mechanism of protected keyword is same as private keyword

It is used in inheritance


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Access Mechanism

Access Specifier Member Functions Class Objects

Public Allowed Allowed

Private Allowed Not Allowed

Protected Allowed Not Allowed


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Defining Member Functions

The member functions must be declared inside the class. They can bedefined:

In Public or Private section of a class

Inside or Outside the class


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Member Function Inside the Class

A. In Public Section:

class item{int codno;

float price;

int qty;

public:

void show()

{

codeno=125;

price=150.00;

qty=200;

cout


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Member Function Inside the Class

B. In Private Section

class item{int codno;

float price;

int qty;

void values()

{

codeno=125;price=150.00;

qty=200;

}

public:

void show()

{

values();

cout


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Member Function Outside the Class

class item{

int codno;float price;

int qty;

public:

void show();

};

void item :: show()

{

codeno=125;

price=150.00;

qty=200;cout


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Have a Nice Day!

02. classes and objects

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