OBJECT ORIENTED PROGRAMMING

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OBJECT ORIENTED PROGRAMMING IN C
July 19, 2004 Elizabeth Sherly
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Objective

• A crash programme on C and thorough
  understanding of object-oriented concepts
• Write C programs using C concepts
• Get a better understanding of solving problems
  using C

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Goal

• Upon the completion of the session, you should be
  able to know
• Structured Programming Object Oriented
  Programming
• Software Retrospection and Need of OOPs
• OOPs- Characteristics
• Classes and Objects

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References

• Programming in C Third edition Bjarne
  Stroustrup
• Microsoft C/Turbo C - Lafore
• C How to program Deitel, Third edition
• Object Oreinted Programming with C, Balagurusamy

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C

• C is a generic programming language, developed
  by Bjarne Stroustrup in early 80s at AT T Lab.
• It is better than C
• Object Oriented Programming
• More appropriate for commercial application and
  system programming

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Software Crisis
Retrospection Software Crisis of 1970s,
characterized by

• poor quality and reliability
• time and cost overruns
• user dissatisfaction

Cause identified as

• inherent complexity of software and
• CABTAB (Code A Bit, Test A Bit) approach towards
• development

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Retrospection (Contd..)

• Real world entities
• Open Interface
• Reusability and extensibility
• Tolerant to any changes in future
• Productivity and decrease software cost
• Quality of software
• Time Schedules
• Software Development process

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Retrospection (Contd.)

• Software Engineering advocated closer attention
  to
• various stages of development such as
  Requirements
• Analysis, Design,Coding and Testing and many
  models
• of sequencing these activities were suggested

• Application of Software Engineering principles
• progressively improved chances of

• Delivery as per schedule
• Customer satisfaction
• Change management
• Re-use

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Object Oriented Programming
Need for a paradigm shift

• Complexity of applications and environments is
• rapidly increasing
• Eg. Programs need to work on many platforms, and
• hence require abstraction for networking and also
  for
• inter-operating dynamically with other software
  on
• these computers)

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Procedural verses Object Oriented

• Emphasis on Functions
• Programs are divided into functions
• Share Global data
• Functions transform data
• Top down Approach

• Emphasis on Data
• Programs are divided into Objects
• Data is hidden and highly protected
• Objects communicate each other using functions
• Bottom-up Approach

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Object Oriented Programming
Object Oriented Approach

• Object oriented approach is fundamentally
  different from traditional process oriented
  approaches
• It has intuitive, yet powerful constructs to
  represent
• real-life entities and their inter-relationships
• It is primarily based on entity abstraction in
  the
• form of objects
• C /JAVA is an Object Oriented language and One
  must understand the underlying concepts of this
  approach to fully utilise the Power of these
  languages
• Object abstracts both its State and behavior,
• rather than separate data and procedural
• abstractions

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OOPs Definition

• Object Oriented Programming is a method of
  implementation in which programs are organized as
  collection of objects, each of which represent an
  instance of classes.
• Object Oriented Programming , Grady Booch
• Object Oriented Programming is an approach that
  provides a way of modularizing programs by
  creating partitioned memory for both data and
  functions that can be used as a template for
  creating copies on demand.
• Object Oriented programming with C,
  Balaguruswamy

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Object Oriented Programming
Object Oriented Modeling

• Unified Modeling Language (UML), used for object
• oriented modeling, provides powerful constructs
  for
• diagrammatic representation of real-life entities
  and
• their inter-relationships, shifting focus even
  into
• analysis phase
• Essentially, analysis models are only extended in
  
• terms of issues like ease of implementation and
• optimization, dynamic interactions, re-use and
• inter-operability etc.

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• 1. Comments
• 2. Load
• 3. main
• 3.1 Print "Welcome to C\n"
• 3.2 exit (return 0)
• Program Output

Welcome to C!
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• Load
• 2. main
• 2.1 Initialize variables integer1, integer2, and
  sum
• 2.2 Print "Enter first integer"
• 2.2.1 Get input2.3 Print "Enter second integer"
  2.3.1 Get input2.4 Add variables and put result
  into sum2.5 Print "Sum is" 2.5.1 Output sum
• 2.6 exit (return 0)
• Program Output

Enter first integer 45 Enter second
integer 72 Sum is 117
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Object Oriented Programming
Abstraction

• A mental process
• Helps to focus attention on exclusively only
  those
• aspects of the concerned real world phenomenon
• relevant to the purpose
• Differ from person-to-person and
  context-to-context
• Eg. Library is a facility for a student
• employer for its staff
• investment for management

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Object Oriented Programming
Abstraction (More Examples)

• In real world
• We abstract crows, sparrows, parrots etc. as
  birds
• buses, boats, aircraft as vehicles
• Children abstract birds and aircraft as Flying
  Things

Abstraction enable us to put "barrier" so that
"complex" details, not relevant to the purpose,
do not confuse us.
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Object Oriented Programming
Abstraction (More Examples)

• In programming (traditional)
• Data abstraction (giving all essential data about
  a
• particular entity)
• Eg. Payslip
• Procedural abstraction (giving various steps
  involved
• in a procedure)
• Eg. Print Payslip

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Object Oriented Programming
Abstraction (More Examples)

• In programming (object oriented)
• We abstract objects both in terms of its behavior
  
• as well as its structure
• Eg. object "pay-slip" represents the abstraction
  of
• details of pay, and
• also functionalities like "compute-net-pay",
• "compute-tax",
• "print-pay-slip"
• ..

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Object Oriented Programming
Abstraction (Contd.)

• Used to separate relevant aspects of behavior
  and
• characteristics of a real-world entity, from the
  actual
• implementation that enables such a behavior.
• That is, it limits the scope of our interest to
  the behavior
• and characteristics of the the real-world entity
  and, thus helps
• in building up a contract or an agreement between
  the object
• and its potential clients (who use these objects)
• This agreement , in turn, defines the
  responsibilities of the real-
• world entity in terms of its behavior and
  characteristics.

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Object Oriented Programming
Encapsulation

• Complimentary aspects of the same mental process
• While abstraction builds up a contract that
  defines
• the behavior, encapsulation ensures the execution
  of
• the contract consistently
• Eg. In the abstraction of the class of Flying
  Things,
• encapsulation hides the fact that an aircraft is
  engine-
• powered while the bird flies by flapping its
  wings
• Encapsulation is achieved by hiding information
  that are not
• required for other objects to interact with it.

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Object Oriented Programming
Encapsulation

• Encapsulations wrap data and its function into a
  single unit.
• Interface defines the behavior common to all
  objects
• of that class while implementation is the inside
  view
• (comprising of the representation and the
  mechanism
• that achieve the behavior) of these objects.
• Keywords like public and private are used, as
  access
• control constructs, to prevent a client from
  accessing
• the implementational secrets of an object.

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Object Oriented Programming
Objects and Classes

• They are the basic building blocks of object
  oriented
• technology
• When entities are abstracted, and the abstraction
  
• defines the class and specific instances
  (examples)
• form the objects
• Class provides the description of an abstraction
• applying to a set of objects sharing a common
• structure and behavior
• Everything about an object is defined in the class

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Object Oriented Programming
Objects

• Objects consist of
• visible behavior and structure as abstracted and
• implementation details encapsulated and hidden

• An object has
• An identity of its own
• State
• Interface by which the clients are serviced
• Implementation of its behavior

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Object Oriented Programming
Object Identity

• Objects thus have a unique existence
• (in memory, from programming point of view)
• Each object is distinguished by its name or
• a reference (to the space in memory it occupies)
• Objects are created at the beginning of their
  life
• span and are destroyed at the end of it
• Identity of an object is the means by which
  clients
• can refer to that object.

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Object Oriented Programming
Object State

• represented by attributes defined as part of its
• structure and its current values
• When an object interacts with other objects,
• and clients perform operations on the object,

• Behavior of the object depends on its state
• and
• Also, methods invoked often alter the state

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Object Oriented Programming
Object Behavior

• Activity, exhibited by the object in response to
  
• operations on it, that is visible outside
• When an object interacts with other objects,
• and clients perform operations on the object,
• behavior of the object depends on its state

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Object Oriented Programming
Methods

• Operations are performed by the client by passing
  
• a message to the object. The operations that can
  be
• performed, and the format of the message (or the
• "signature" that has to be passed), are defined
  in
• the class as "methods
• All the methods of a class together constitute
  the
• interface used by the client
• Methods are implemented as functions in the class
• Terms operations, messages, methods, and member-
• functions are all used interchangeably

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Object Oriented Programming
Methods (Contd)
Two other essential operations are

• Constructor initializing the state of an object
• (when it is created)
• Destructor freeing the state and destroys the
  object itself

Constructors make sure that the object is well
created, and hence can receive messages. Eg.
Say, Account object has methods such as
withdraw() and deposit(), and the current
balance as its state. Minimum deposit should be
made before opening an account, and before one
can do any transactions on that account.
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Object Oriented Programming
Classes

• Describes the interface and the implementation of
  
• the set of objects
• Interface of a class provides outside view (like
  a
• contractual agreement) and declares the expected
  
• behavior of objects of this class in the context
  of
• interaction with other objects.
• Implementation of a class is the inside view or
  the
• Implementor's View of how the the behavior as
• defined in the interface is accomplished.

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• friend function and friend classes
• Can access private and protected members of
  another class
• friend functions are not member functions of
  class
• Defined outside of class scope
• Properties of friendship
• Friendship is granted, not taken
• Not symmetric (if B a friend of A, A not
  necessarily a friend of B)
• Not transitive (if A a friend of B, B a friend of
  C, A not necessarily a friend of C)

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Friend Functions and Friend Classes

• friend declarations
• To declare a friend function
• Type friend before the function prototype in the
  class that is giving friendship
• friend int myFunction( int x )
• should appear in the class giving friendship
• To declare a friend class
• Type friend class Classname in the class that is
  giving friendship
• if ClassOne is granting friendship to ClassTwo,
  friend class ClassTwo
• should appear in ClassOne's definition

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• 1. Class definition
• 1.1 Declare function a friend
• 1.2 Function definition
• 1.3 Initialize Count object

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• 2. Modify object
• 3. Print results
• Program Output

counter.x after instantiation 0 counter.x after
call to setX friend function 8
Write a program to find the average of two values
using friend function
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Operator Overloading

• Enabling Cs operators to work with class
  objects
• Ability to provide operators with special meaning
• Requires great care when overloading is misused,
  program difficult to understand
• Examples of already overloaded operators
• Operator and the bitwise left-shift operator
• and -, perform arithmetic on multiple types
• Compiler generates the appropriate code based on
  the manner in which the operator is used

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Restrictions on Operator Overloading

• C operators that can be overloaded
• C Operators that cannot be overloaded

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• Overloading an operator
• Write function definition as normal
• Function name is keyword operator followed by the
  symbol for the operator being overloaded
• operator used to overload the addition operator
  ()
• It may be either a member function or friend
  function
• Using operators
• To use an operator on a class object it must be
  overloaded unless the assignment operator()or
  the address operator()
• Returntype classnameoperator op()
• Vector operator (vector)
• Cmplx operator(double r)

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Restrictions on Operator Overloading

• Overloading restrictions
• Precedence of an operator cannot be changed
• Associativity of an operator cannot be changed
• Unary operators remain unary, and binary
  operators remain binary
• Operators , , and - each have unary and
  binary versions
• Unary and binary versions can be overloaded
  separately
• No new operators can be created
• Use only existing operators
• No overloading operators for built-in types
• Cannot change how two integers are added

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Operator Functions as Class Members vs. as friend
Functions

• Member vs non-member
• Operator functions can be member or non-member
  functions
• When overloading ( ), , - or any of the
  assignment operators, must use a member function
  
• Operator functions as member functions
• Leftmost operand must be an object (or reference
  to an object) of the class
• If left operand of a different type, operator
  function must be a non-member function
• Operator functions as non-member functions
• Must be friends if needs to access private or
  protected members
• Enable the operator to be commutative

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include include class
complex float rp float im public complex()
complex(float r, float i) rpr imi
complex operator(complex) void
display() complex complexoperator(complex
c) complex temp temp.rp rp c.rp temp.im
im c.im return(temp)
void complexdisplay() cout rp
void main() complex c1,c2,c3 c1complex(2.
5,3.5) c2complex(1.6,2.7) c3 c1 c2
//c3 c1.operator(c2) cout
cout
ay()
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• It receives only one complex type argument
  explicitly
• It returns a complex value
• Member function can be invoked only by an object
• Here c1 takes the responsibility of invoking the
  function and c2 plays the role of argument that
  is passed to the function.

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Overloading using Friends

• Friend function require two arguments to be
  explicitly passed.
• In complex example
• Replace member fn declaration as
• Friend complex operator(complex, complex)

• Redefine the operator fn as
• Complex operator (complex a, complex b)
• temp.rp a.rp b.rp
• temp.im a.im b.im)
• return (temp)

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Friend istream operator(istream istr,cmplx
r) Friend ostream operatorcmplx r) Istream operator(istream istr,
cmplx r) istr r.rp istr r.im Return
istr
Ostream operatorr) Ostr
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Useful Links in C

• Classes
• Classes are the standard unit of programming
• A class is like a blueprint reusable
• Objects are instantiated (created) from the class
  
• For example, a house is an instance of a
  blueprint class
• Introduction to Programming in C
• http//www. c Annotations/

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Object Oriented Programming
What is Inheritance ?

• Feature enabling classes to be derived from other
  classes,
• having similar behavior and structure but having
  higher
• levels of abstraction
• Denotes IS-A relationship and implies
  specialization
• Subclasses inherit the interface, the attributes
  and the
• implementation from the super-classes
• Sub-class may need to know about methods and
  attributes
• of super-class. This is facilitated using
  protected keyword
• Such methods and attributes would be accessible
  to sub-
• classes but prevent access to outside objects)

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Object Oriented Programming
Inheritance Hierarchy

• Captures hierarchy that exists among real life
  entities,
• ordering abstraction to different levels
• Hierarchical representation helps in
  comprehension
• of abstraction of entities, making object model
  more
• comprehensive and elegant
• Abstracting crows, parrots, and sparrows into
  birds and
• then describing each in terms of birds is more
  intuitive,
• as against having each of them as separate,
  independent
• classes with methods like fly, sing etc. defined
  for each.

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Object Oriented Programming
Inheritance Hierarchy (Contd)

• Higher levels of this hierarchy easily
  comprehended

• Flying thing is identified even by a child
• Difference between a military and a civil
  aircraft
• understood by the general public
• But, probably, only experts can point out
  difference
• between a Bomber or a Fighter.

• Defining one in terms immediately higher one
  easier

• Explaining Vulture in terms of wildlife birds is
  easy

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Object Oriented Programming
Inheritance Hierarchy (Example)
Flying Thing
Aircraft
Bird
Wild
Civilian
Military
Domestic
Bomber
Crow
Sparrow
Fighter
Hawk
Vulture
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Object Oriented Programming
Inheritance (facilitating reuse in design and
programming)
Bird
eat() fly() land() takeOff()
Crow
Sparrow
caw()
chirp()
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Object Oriented Programming
Inheritance (A finer abstraction)
Bird
eat() fly() land() takeOff() sing()
Crow
Sparrow
sing()
sing()

• Method sing() added to classes Crow and Sparrow
• These methods override sing() method in the
  super-class Bird.

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Multiple Inheritance
Single Inheritance
B
A
A
B
C
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Multilevel Inheritance
Hierarchical Inheritance
A
A
B
B
C
D
C
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Hybrid Inheritance
A
B
C
D
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Defining Derived Classes
Class derived class name visibility mode base
class name -------- ----------
Class ABC private XYZ // private
Derivation Class ABC public XYZ Class ABC
protected XYZ
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Public Private visibility

• Base class Derived Class
• Private
• Public Public Private

Public Private Not inherited Not.
In
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Protected visibility

• A member declared as protected is accessible by
  the member functions within its class and any
  class immediately derived from it.
• When a protected member is inherited in public
  mode, it becomes protected in derived class. It
  is ready for further inheritance
• A Protected member, inherited in private mode, it
  becomes private in the derived class. But not
  further inherited.

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public, private, and protected Inheritance
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include class B int
a public int b void get_ab() int
get_a() void show_a() class D public
B int c public void mul() void display()

void Bget_ab() a5 b10 int
Bget_a() return a void Bshow_a()
cout void D display() cout l cout
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void main() D d d.get_ab() d.
mul() d.show_a() d.display() d.b
20 d.mul() d.display()
Output a5 a5 b10 c50 a5 b20 c100
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Multiple Inheritance

• A class can inherit the attributes of two or more
  classes.
• Multiple Inheritance

A
C
B
Class D public A, public B ------
D
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Hybrid Inheritance

• There could be situations where we need to apply
  two or more types of inheritance to design a
  program. For example

Student
Example
test
Sports
Multilevel Multiple
Result
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VIRTUAL BASE CLASSES
There are situations where we would require the
use of both the multiple and multilevel, and
hierarchical inheritance.
A
B
C
D
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All the public and protected members of A is
inherited to D twice, this cause duplication.
The duplication of inherited members due to
these multiple paths can be avoided by making
the common base class called virtual base class
Class B1 virtual public A Class B2 public
virtual A
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Object Oriented Programming
What is Polymorphism ?

• Feature enabling objects of different classes to
  behave
• differently to the same message
• One name, multiple form
• Also known as Late binding, runtime linking
• Message to an object of an inherited class result
  in
• invoking corresponding method of its super-class
• However, super-class methods may be over-ridden
  in
• its sub-classes
• Design and implement systems that are more easily
  extensible

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Object Oriented Programming
Polymorphism (Implementation)

• Mechanism, dynamically binding the correct
• implementation of the method to the reference, is
  
• used to effect polymorphism
• In interpreted languages like Java, the
  interpreter keeps
• track of the class of an object referred, while
  in case of
• compiled languages like C, the compiler
  typically
• uses 'virtual function tables.

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Object Oriented Programming
Advantages of Inheritance

• Captures similarity and differences in the real
  world
• entities and their inter-relationships
• Facilitates re-use
• New specialised classes can be created from Class
  
• libraries, adding new functionalities as desired

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Object Oriented Programming
Dis-advantages of Inheritance

• Violates the principle of encapsulation
• Inheritance may also lead to unmanageable no. of
  
• class hierarchies.
• Misusing may affect re-use as inheritance
  relations
• between classes are bound during compilation and
• hence the code using inheritance cannot overcome
• dependencies showing up during runtime)

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Object Pointers and this

• C also uses pointers to point to an object
  created by a class.
• ex. Item it_ptr
• This Pointer Points to an object for which this
  function is called.
• ex. A function call A.max() will set the pointer
  this to the address of the object A.

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Pointers to Derived Class

• A single pointer can be used in base as well as
  derived class.
• If B is a base class and D is a derived class,
  then a pointer to B can also be pointer to D.
• B ptr
• B b D d
• ptr b //ptr points to object b
• ptr d //ptr points to object d

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• Ptr can use to access the members of B and the
  members of D that are inherited from B
• But not the members that originally belong to D.
• Example

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virtual Functions

• virtual functions
• Suppose a set of shape classes such as Circle,
  Triangle, etc.
• Every shape has own unique draw function but
  possible to call them by calling the draw
  function of base class Shape
• Compiler determines dynamically (i.e., at run
  time) which to call
• In base-class declare draw to be virtual
• Override draw in each of the derived classes

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Virtual Functions

• In previous example, the compiler ignore the
  contents of the pointer, and chooses the member
  function that matched the type of the pointer.
• When you use same function name in both base and
  derived classes, the function in base is declared
  as virtual.
• When a function is made virtual, C determines
  which function to use at runtime based on the
  type of the object pointed to, rather than the
  type of the pointer.

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• virtual declaration
• Keyword virtual before function prototype in
  base-class
• virtual void show()
• A base-class pointer to a derived class object
  will call the correct show function
• bptr- show()
• If a derived class does not define a virtual
  function, the function is inherited from the base
  class

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Rules for Virtual Functions

• Virtual functions must be members of class
• They cannot be static members
• They are accessed by using object pointers
• It can be a friend function also
• We cannot have virtual constructors, but can have
  virtual destructors

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Pure Virtual Functions

• A do-nothing function that can be defined in
  base class for implementing in derived classes.
• Virtual void show()0
• Such functions are called pure virtual functions.
• Example Find out the volume and area of circle,
  cylinder by using virtual functions.

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Object Oriented Programming
Abstract Methods Classes

• Method specified in a class without
  implementation
• is called abstract method
• (Eg. Method sing can be specified in Bird
  class but
• implemented on a sub-class)
• Class having abstract methods is called an
  abstract
• class
• Instances of an abstract class cannot be created
• (as complete behavior of the class is undefined
  and
• would not be able to fulfil the contract without
  help
• from its sub-classes)

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Object Oriented Programming
Abstract Classes

• One of the important concepts in object-oriented
• programming and design
• Provides a higher form of generalization
• An abstract class can have attributes and other
• non-abstract methods
• Class Bird could have an attribute 'sex and also
  
• behaviors eat(), fly() etc, of which eat may be
  fully
• implemented the class itself.