Object Oriented Programming Using C++

Using
C++
Object Oriented Programming

Contents
 Features of OOP
 Classes
 Objects & Creating the Objects
 Constructors & Destructors
 Friend Functions & Classes
 Static data members & functions

OOP
 It is programming technique in which programs are written on the
basis of objects
 It is a powerful technique to develop software.
 It is used to analyze and design the application in terms of objects.
 It deals with data and the procedures as a single unit
 Interacting objects handle their own house-keeping.
 Objects in a program interact by sending messages to each other.
 Each object is responsible to initialize and destroy itself.
 There is no need to explicitly call a creation or termination procedure

Features of object-oriented programming
 Data abstraction
the procedure to define a class from objects.
 Encapsulation
A technique for Information Hiding.
 Inheritance
It allows to define a class in terms of another class, which makes it easier
to create and maintain an application.
 Dynamic binding
It determining the method to invoke at runtime instead of at compile time
 Polymorphism
The word polymorphism means having many forms.
Typically, polymorphism occurs when there is a hierarchy of classes and
they are related by inheritance.

Effects of OO methodology on software design
 Maintenance
 Extensibility
 Reusability

Objects
 Object represents an entity in the real world
 Identified by its name
 It consists of two things:
Properties: Characteristics of an object
Functions Actions performed by the object
o Everything is an object
o Systems are composed of objects

 Everything is an object
 A student, a professor
 A desk, a chair, a classroom, a building
 A university, a city, a country
 The world, the universe
 A subject such as CS, IS, Math, History, …
 Systems are composed of objects
 An educational system
 An economic system
 An information system
 A computer system

Design Methodologies
Object-Orientation is a design methodology
 Objects are the building blocks of a program
(interface, editor, menu, file, etc.); data managing
object (db), etc.)
 Objects represent real-world abstractions within an
application.

Properties of Objects
 Characteristics of an object are known as Properties or
attributes of the object
 Each object has its own properties
Example:
 If “Person” is an object, it has following properties
 Name
 Age
 Weight
Object: Car
Properties: Model, Color, Price

Functions of an Object
 Tasks or actions performed by the object are known
as functions or methods.

Classes
 Collection of objects with same
properties and functions
 Use to define characteristics of the
object
 Used as a model for creating different
objects of same type
 Each object of a class is known as an
instance of the class

Declaring a class
 Keyword “class” is used to declare a class
 Declaration specifies:
 Member Variable / Data member
 Function / Member Function
These are common to all objects of that class
Syntax:
class identifier
{
Body of the class
};
Class: is the keyword
Identifier: name of the class to be declared

Access Specifiers
 It specifies the access level of the class members
 Two common access specifiers are:
 Private:
Restrict the use of the class members within the class. It is the default
access specifier. It is used to protect the data members from direct
access from outside the class. Data Member are normally declared with
private access specifier.
 Public
It allows the user to access members within the class as well as outside
the class. It can be accessed from anywhere in the program. Member
functions are normally declared with public access specifier.

Creating objects
 Class is simply a model or prototype for creating objects.
 It is like a new data type that contains both data and
functions.
 Object is created in the same way as other variables are
created.
 Object is also known as instance of a class.
 Process of creating an object is also called instantiation.
Syntax:
class_name object_name;
Class_name: name of the class whose type of object is to be created
Object_name: object to be created.

Executing Member Functions
 Member functions are used to manipulate data
members of a class.
 Member functions can be executed only after
creating objects
Syntax:
Object_name.function();
Object_name: name of object whose member function is to be executed
Function: It is the member function that is need to be executed.

Write a program that
declares a class with a
data member and two
member functions
OUTPUT:
enter number 10
the value of n= 10

Defining member functions outside class
 Function declaration is specified within the class
 Function definition is specified outside the class
 Scope resolution operator :: is used in function declaration if
the function is defined outside the class.
Syntax:
Return_type class_name :: function_name(parameters)
{
function body
}
Return_type type of value to be returned by function
class_name class name to which function belongs
:: scope resoltion operator
function_name name of funtio to be defined

Constructors
 Type of member function that is automatically executed when
an object of that class is created is known as constructor
 It has no return type
 It has same name that of class name
 It work as normal function but cannot return any value
 It is used to initialize data memebrs
Syntax:
name()
{
Constructor body
}
Name: it indicate the name of the constructor

Passing parameters to constructor
 It is same as passing parameters to normal functions
 Only difference is
 Parameters are passed to the constructor when the object is
declared.
Syntax:
type object_name(parameters);
Type: it is the name of the class (type of the object to be declared)
Object_name: name of the object to be declared
Parameter: list of parameters passed to the constructor

Constructor overloading
 Declaring multiple constructors with the same name
but different parameters
 It must differ in one of the following ways
 Number of parameters
 Type of parameter
 Sequence of parameters

Output
the constructor of first=
num = 0
ch = x
the contents of second =
num = 100
ch = p

Default copy constructor
 It is available by default in all classes
 It is used to initialize an object with another object of the
same type.
 User does not need to write this constructor
 It accepts a single object of the same type as parameter.
Syntax:
Class_name object_name(parameter); OR
Class_name object_name = parameter;
Class_name: type of object to be created
Object_name: name of the object
Parameter: name of parameter passed to default constructor

Destructors
 Member function that is automatically executed when an
object of that class is destroyed in known as destructor
 Is has no return type
 Name is same as the class
 It also cannot accept any parameter
 Constructor name proceeded by tilde sign ~
Syntax:
~name()
{
destructor body
}

Objects as function Parameters or Return Type
As parameters:
 Objects can also be passed as parameters to member
functions
 Method is same as passing parameters to other functions
As return type:
 Returning an object from member function is same as
returning a simple variable
 Its return type should be the same as the return type of
the object to be returned.

Static data member
 The type of data member that is shared among all the
objects of the class is known as static data members.
 Defined with static keyword
 If defined static member; only one variable is created in
memory even if there are many objects of that class
 Used to share some data among all objects of a particular
class
 Visible only in the class in which it is defined
 Its lifetime:
 Starts when the program starts its execution
 Ends when the entire program is terminated

Object Oriented Programming Using C++

Difference between normal and static data members
A
B
N
A
B
A
B
A
B
N
1 2
10
100
10
1
200
20
1
1
200n
Object b1 Object b2 Object b2Object b1
Three normal data members
Two normal data members (a,b) and one
static member (n)

Friend Functions
 Function that is allowed to access the private and protected
members of a particular class from outside the class is
called friend functions
 Friend function of a class
 Not a member function
 Has direct access to private members
Just as member functions do
 Use keyword friend in front of
function declaration
 Specified IN class definition
 But they’re NOT member functions!

Friend Classes
 Entire classes can be friends
 Similar to function being friend to class
 Example:
class F is friend of class C
 All class F member functions are friends of C
 NOT reciprocated
 Friendship granted, not taken
Syntax:
friend class F
 Goes inside class definition of "authorizing" class

Static Function
 A function may be declared with the static keyword
 Static functions live at class level, not at object level
 Static functions may access static variables and
methods, but not dynamic ones
Syntax:
public static int getNumSold(){
return numTicketsSold;
}

class test
{
private:
static int n;
public:
static void show()
{
cout<<“n = “<<n;
}
};
int test::n = 10;
void main()
{
test::show();
getch();
}
Output
n = 10

1 . Write a program that creates three objects of a
class student. Each object of the class must be
assigned a unique roll number.
2. Compare OOP & structured programming
Assignment

Object Oriented Programming Using C++

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