Object Oriented Concepts Class & Objects in C++ Constructor & Destructors in C++ Operator Overloading in C++ Friend function in C++ Data Conversion in C++ This pointer in C++ Friend class in C++ Nested Class in C++

1. OOP/AKN/Part_II/1
Object Oriented Programming
Concepts
Part II
Ajit K Nayak, Ph.D.
SOA University

2. OOP/AKN/Part_II/2
Contents
 Object Oriented Concepts
 Class & Objects
 Constructor & Destrctors
 Operator Overloading
 Friend function
 Data Conversion
 This pointer
 Friend class
 Nested Class

3. OOP/AKN/Part_II/3
How to Solve a Complex System?
 The Technique of mastering complexity has
been known since ancient times “Divide and
Rule” …Dijkstra
i.e Decomposition of the Problem
 Intelligent decomposition directly addresses
the inherent complexity of software by forcing
a division of systems state space
…Parnas

4. OOP/AKN/Part_II/4
Decomposition
 Algorithmic/Functional Decomposition
1. Divide the system to some modules
2. Each module should denote a major step
in overall process.
 Object Oriented Decomposition
1. View the world as a set of autonomous
agents that collaborate to perform some
higher level behaviour.

5. OOP/AKN/Part_II/5
Functional Decomposition
The System
Function1 Function2 Function3
Function11 Function12
. . . . . .
. . . . . .
. . . . . .

6. OOP/AKN/Part_II/6
OO Decomposition
Autonomous Agents(Objects)
Agent3
Agent1
Agent4
Agent2
msg1
msg2
msg4
msg3

7. OOP/AKN/Part_II/7
Functional decomposition
Main
Problem: No. of words in a file
getWordFromFile addToWordList
getWordList sortword checkWord
Sorted Words
Word List Flag
Words Words(prev,curr)
WordWord Words
getSortedWordList countDiffWords printResult
Sorted Words
Sorted Words
Count
Count

8. OOP/AKN/Part_II/8
OO Decomposition
Problem: No. of words in a file
File
WordList
getWord
Autonomous Agents(Objects)

9. OOP/AKN/Part_II/9
Which is the Right way?
 Algorithmic view highlights the ordering of
events
 Object Oriented view emphasizes the agents
(objects) that either cause action or to be
acted upon
 Both The Philosophy are important
 If the system is Very large, Complex, to be
Extended, Maintained then choose OO
approach.

10. OOP/AKN/Part_II/10
Procedural Programming
 With procedural programming,
you are able to combine
sequences of calling statements
into one single place.
 A procedure call is used to invoke
the procedure. After the
sequence is processed, flow of
control proceeds right after the
position where the call was made
.
Main
Program
Procedure

11. OOP/AKN/Part_II/11
 Now a program can be viewed as a
sequence of procedure calls.
 The main program is responsible to pass
data to the individual calls, the data is
processed by the procedures and the
resulting data is presented.
 Thus, the flow of data can be illustrated as a
hierarchical graph, a tree.
Procedural Programming

12. OOP/AKN/Part_II/12
Procedure Program view
Main Program
Data
Procedure1
Procedure2 Procedure3
Procedural Programming uses Algorithms as the
Basic building block.

13. OOP/AKN/Part_II/13
Features of
Object Oriented Programming
 Abstraction
Encapsulation
 Composition
 Aggregation
 Association
 Inheritance
 Polymorphism
 Dynamic Binding

14. OOP/AKN/Part_II/14
Abstraction
 An Abstraction denotes the Essential
characteristics of an object that
distinguishes it from all other kinds of
objects and thus defines sharply defined
conceptual boundaries, relative to the
perspective of the viewer.
…Grady Booch

15. OOP/AKN/Part_II/15
Abstraction

16. OOP/AKN/Part_II/16
Abstraction(contd.)
 It focuses on the outside view(interface) of an
object. Therefore, it serves to separate an
objects essential behaviour from its
implementation.
 It is used to reduce complexity by ignoring some
aspect of a subject that are not relevant to the
current purpose.
Example : A MAP (is not an exact picture)
 Only the essential features of an area are
shown
 Unimportant features are ignored.

17. OOP/AKN/Part_II/17
Abstraction(contd.)
 All Abstractions have static as well as dynamic
properties.
Example: A FILE
Static : Name, Size, Content
Dynamic: the value contained in static properties.
 It is dynamic because a file may grow or shrink
in size
 Its name and content may change

18. OOP/AKN/Part_II/18
Encapsulation

19. OOP/AKN/Part_II/19
Encapsulation(contd.)
 It is the process of compartmentalising
the elements of an abstraction that
constitute its structure and behaviour.
…Grady Booch
• In this process we keep the properties (or
structure or states) and behaviour of an
object in one place bundeled together.
• It supports information hiding
i.e. hiding all the information that is
unnecessary to the outside world.

20. OOP/AKN/Part_II/20
Encapsulation
 Encapsulation helps to achieve abstraction by
hiding the implementation of behaviours
 It provides explicit barriers among different
abstractions
Example: Riding a Bike
• Most of the riders are ignorant about the detail
structure of an IC Engine.
• Changing gears on your bike need not require to
know “how the gear mechanism works” just need
to know which lever to move.

21. OOP/AKN/Part_II/21
 Composition defines a has-a relationship
 An organized collection of components
interacting to achieve a coherent, common
behavior
 The automobile has a windshield.
 It deals with a single, complex system as an
organization of more numerous but simpler
systems
Composition

22. OOP/AKN/Part_II/22
Composition (examples)
A human being consists of a respiratory
system, a circulatory system, an immune
system, a nervous systems, a skeletal
system, etc
An aircraft consists of a propulsion system, a
control system, a navigation system, etc
An operating system consists of a user
interface, a file system, a network system, a
memory management system, etc

23. OOP/AKN/Part_II/23
Example: Composition
CPU
Memory
Disk
processorKey Board
Monitor
Mouse
Modem
Aggregation
Association

24. OOP/AKN/Part_II/24
Plant is a part of Garden(whole) (Association)
Flower is a part of Plant(whole) (Aggregation)
• Garden permits different plants to be raised over
time.
• Replacing a plant does not change the identity of a
garden.
• Removing a Garden does not necessarily destroy all
of its plants
i.e. the life time of Plant(part) and Garden (whole) are
independent.
Example

25. OOP/AKN/Part_II/25
 Inheritance is the most important is-a kind
of hierarchy
Inheritance helps to share the structure and
behaviour defined in one or more classes
…Grady Booch
i.e a sub-class inherits from one or more
super-classes and subclass is dependent
upon superclass
Inheritance

26. OOP/AKN/Part_II/26
Inheritance(is a kind of)

27. OOP/AKN/Part_II/27
Examples (Inheritance)
 Mammal is a kind of Animal
 Tiger is a kind of Mammal
 Cheetah is a kind of Tiger
 House is a kind of Tangible Asset
 Quick sort is a kind of Sorting algo
Sub class?
Super Class?

28. OOP/AKN/Part_II/28
Examples (contd.)
Vehicle
Land Vehicle Water Vehicle
BoatCar Amphibious Vehicle

29. OOP/AKN/Part_II/29
Inheritance(contd.)
 It implies a Generalization/Specialization
hierarchy
i.e subclass specializes its superclass and
superclass generalizes its subclass
 Its benefits are
Extensibility,Maintainability,Reusability,
Understandability,Abstraction, and
Substitutability

30. OOP/AKN/Part_II/30
Polymorphism
 It is the property that allows to exhibit
different behaviours at different situations
 Different objects respond differently to a
same message
Example: message draw
Circle responds with drawing a circle
Polygon responds with drawing a polygon
…

31. OOP/AKN/Part_II/31
Dynamic Binding
 (Also called as Late binding) Code
associated with a given message will be
decided at run time
 Helps achieving dynamic polymorphism

32. OOP/AKN/Part_II/32
Object1
Data1+Procedures1
Data Data1 Object3
Data3 + Procedures3
Object2
Data2 + Procedures2
Object4
Data4 + Procedures4

33. OOP/AKN/Part_II/33
Object-Oriented Programming
 Is a pool of objects. They interact with
each other by passing messages.
 Each object implements its own module.

34. OOP/AKN/Part_II/34
Object
What we mean?
• Humans understand the world by
viewing it as composed of
autonomous, interacting objects.
• Examples: people, animals, phone,
desks, buildings, stairs, ...

35. OOP/AKN/Part_II/35
Which is an Object?
An object may be of any of the following
 A Tangible and/or Visible thing
A Table, A Tiger, A Car
 Something that may be apprehended
intellectually
A Bank Account, A Complex Number
 Something towards which thought or action
is directed
A Date, Time

36. OOP/AKN/Part_II/36
Virtual Objects
Objects that live in programs only, you can
not see by eyes, feel by hand, smell by
nose, and taste by tongue.
Virtual objects are the basic components for
your object-oriented programs.

37. OOP/AKN/Part_II/37
Examples of Virtual Objects
Bank Account
 Keeps balance; responds to messages to deposit,
withdraw, and get balance
Set
 Elements can be added, deleted, queried for
presence.
GUI Window
 Ultimately responsible for keeping contents of
window. Many operations possible including open,
close, maximize, minimize, move, etc.

38. OOP/AKN/Part_II/38
Every thing are Objects?
 Some objects may be tangible but have fuzzy
physical boundaries(fog, river) may not
be(sometimes) considered as objects
 Difficult to distinguish my fog from your fog
 But in a weather map; a fog bank over odisha is a distinctly
different object than a fog bank over Maharastra
 Beauty, color, emotions(love, anger) may be
considered as properties of objects rather than
objects.
 A Man(an object) loves his wife(another object)
 The Cat(an object) is gray

39. OOP/AKN/Part_II/39
Defining an Object
An object has state, behavior, and identity;
the structure and behavior of similar objects
are defined in their common class; the
terms instance and object are
interchangeable
… Grady Booch

40. OOP/AKN/Part_II/40
State
The State of an object encompasses all of the
properties(static property) of the object plus
the current value (dynamic properties) of
these properties.
… Grady Booch
Example: Object :A-320:IC878 (An Air Craft)
States: Fuel = 1000 lts
Temp = 75 oC
Pressure = 200 lbs
isStart = false
…
Dynamic
PropertiesStatic
Properties

41. OOP/AKN/Part_II/41
The state
The state shows the existence of an object
When a person is dead, he has no
functions, but their DS is still there if he is
not burnt.
Also called attributes, private space,
member variables, instance variables, data
members, structure of objects etc…

42. OOP/AKN/Part_II/42
Behavior
Example: Object :A-320:IC878
start(…) : if isstart is false, fuel  x lts, …
run(…) : if isStart is true, …
fly(…) : …
stop(…) : if isStart is true, …
Similarly:
fly causes decreasing in fuel and increasing
in temperature i.e change of states

43. OOP/AKN/Part_II/43
Behavior
Behavior is how an object acts and reacts,
in terms of its state changes and message
passing.
… Grady Booch
Example: Object :A-320:IC878
start, run, fly, break, stop, turn …
Behavior of an object is influenced by its
state and vice versa

44. OOP/AKN/Part_II/44
Behavior / Method
A method is an operation an object can make
to respond relevant message.
A method is associated with a class. An
object invokes a method as a reaction to
receipt of a message.
When an object has no method, it is dead!
Also called member functions, operations,
behaviors or services.

45. OOP/AKN/Part_II/45
Message
A message is a request to an object to
invoke one of its methods. A message
therefore contains
the name of the method and
the arguments of the method.
Consequently, invocation of a method is just
a reaction caused by receipt of a message.
This is only possible, if the method is actually
known to the object.

46. OOP/AKN/Part_II/46
Message
integer i; /* Define a new object */
i.setValue(1); /* Set its value to 1 */
To express the fact, that the integer object i
should set its value to 1.
The message is “Apply method setValue with
argument 1” (sent to object i). We notate the
sending of a message with the help of .(dot)

47. OOP/AKN/Part_II/47
Identity
It is that property of an object which
distinguishes it from all other objects
… Grady Booch
Two objects may have same static and
dynamic properties. But the identity
differentiates them
Example:
SSN, EmpID, Slno, …

48. OOP/AKN/Part_II/48
Object has State Behavior and identity

49. OOP/AKN/Part_II/49
Class(contd.)
It defines a set of objects that share a
common structure and behaviors
… Grady Booch
A class represents only an abstraction, the
essence of an object. It doesn't exist in time
and space
Example: Class Mammal represents the
characteristics common to all mammals
 To identify a particular Mammal, we say
This Mammal or that Mammal

50. OOP/AKN/Part_II/50
Examples of class
 Class horse
Structure:
Age
Weight
Color
Behaviour:
Drag
Run
ride

51. OOP/AKN/Part_II/51
Class

52. OOP/AKN/Part_II/52
Interface of a Class
 The interface of a class provides its outside view
and therefore, emphasizes the abstraction while
hiding its structure and the secrets of its behavior
 The interface primarily consists of the declarations
of all operations applicable to its instances
 But it may also include the declaration of other
classes, constants, variables and exceptions as
needed to complete the abstraction

53. OOP/AKN/Part_II/53
Interface(contd.)
 The Interface of a class may be divided
into three parts
1. Public: declaration that is visible to all the
world
2. Protected: declaration that is visible to the
class itself, its subclasses, and its friends
3. Private: declaration that is visible only to
the class itself and its friends.
Also called access specifiers

54. OOP/AKN/Part_II/54
An Example
class Time{
public:
Time();
void setTime(int,int,int);
void printTime(void);
private:
int hour;
int min;
int sec;
};
Class Name
Attributes / Data
members
Interface
messages /member
functions
Member Access Specifier

55. OOP/AKN/Part_II/55
Example (contd)
Time::Time(){hour=min=sec=0;}
void Time::setTime(int h, int
m, int s){
hour = h; min=m; sec=s;
}
void Time::printTime(void){
cout<<hour“:”<<min<<“:”<<sec;
cout<<endl;
}
Implementation
Constructor
Operations / Methods /
Member functions

56. OOP/AKN/Part_II/56
Example (contd)
main(){
Time t;
cout<<“intial time:”;
t.printTime();
t.setTime(13,27,6);
cout<<“after setting time:”;
t.printTime();
}
An Object / Instance
of Time type
Member access
operator

57. OOP/AKN/Part_II/57
Instantiation
 The mechanism of creating new objects from a
class definition is called instantiation mechanism.
 Every class has such a mechanism.
Static instantiation and Dynamic instantiation.
instantiation at compile time;
instantiation at run time.
 Dynamic instantiation requires a run time support for
allocation and de-allocation of memory.

58. OOP/AKN/Part_II/58
Structure vs Class in C++
A structure is simply a class whose
members are public by default.
class Time{
int hour;
int min;
int sec;
public:
Time();
void setTime(int,int,int);
void printTime(void);
};
struct Time{
int hour;
int min;
int sec;
public:
Time();
void
setTime(int,int,int);
void printTime(void)};
Public by
default
Private by
default

59. OOP/AKN/Part_II/59
Other Definitions for Objects
Anything, real, or abstract, about which
we store data and those methods
(operations) that manipulate the data.”
…Martin/Odell
 An object is an instance of a class. It can be
uniquely identified by its name and it defines a
state which is represented by the values of its
attributes at a particular time.
…Peter Müller

60. OOP/AKN/Part_II/60
Constructors
Constructor is used to initialize(reserves
memory as well as set values to the data
members) an object and it is recognized by
having the same name as the class.
Constructors can be overloaded i.e. there
may be more than one constructors for the
same class with several ways of initialization
Example: Time(), Time(int),
Time(int,int,int), …

61. OOP/AKN/Part_II/61
Constructors
 Every time an object is created, one constructor
is invoked
 Constructors with no arguments is known as the
default constructor
 Constructor can‟t have a return type
 It should always be declared in public part of the
class structure. (?)
 If no constructor is provided by the programmer
then compiler provides one default constructor.
ClassName(){}

62. OOP/AKN/Part_II/62
Destructors
 It is a special member function named same as the
class and preceded by a ~
Example:
class Time{
… public:
~Time();
}
 It is used to free the state of an object
 These are called implicitly when an automatic
object goes out of scope. But if an object is
initialized using new than it has to be deleted
 In very unusual situations does the user need to
call a destructor explicitly!

63. OOP/AKN/Part_II/63
Design a class ComplexNum with Attributes
real (double), img (double) and
Member Functions
Default constructor, parameterized constructor
printComplex, addComplex
Write a main function in which three objects
are created.
Two of them using parameterized constructor, one
using default constructor.
Now add first two objects using addComplex
member function and store the result in third
complex number.
Finally print all the complex numbers.

64. OOP/AKN/Part_II/64
Complex number Program
class ComplexNum{
private:
double real; double img;
public:
ComplexNum(){real=img=0.0;}
ComplexNum(double r, double i){
real = r; img = i;
}
void printComplex();
ComplexNum addComplex(ComplexNum);
}; // end of class definition

65. OOP/AKN/Part_II/65
Main Function
main(){
ComplexNum c1(4,5);
ComplexNum c2(3,4);
ComplexNum c3;
c3 = c1.addComplex (c2);
c1.printComplex();
c2.printComplex();
c3.printComplex();
}

66. OOP/AKN/Part_II/66
Method implementation
void ComplexNum::printComplex() {
cout<<real<<“+ i ”<< img <<endl;
}
ComplexNum ComplexNum:: addComplex(
ComplexNum x) {
ComplexNum z;
z.real = x.real + real;
z.img = x.img + img;
return z;
}

67. OOP/AKN/Part_II/67
Constant Member Functions
int func(…) const;
 const is a specifier, which specifies that, this
function will not modify the states of an object.
 The value of the object can‟t be changed
 The keyword is written after the parentheses
Example:
class Date{
private:
int d,m,y;
public:
int day()const{return d;}
int month()const{return m;}

68. OOP/AKN/Part_II/68
Constant Member Functions(contd.)
int year()const;
int addYear(int);
};// end of class definition
int Date::year() const{return y++;}
// Error: Attempt to change value of y
int Date::year() const{return y;}
// Ok
int Date::year() {return y;}
// Error: const keyword missing
int Date::addYear(int a){return y+a;}
// Ok

69. OOP/AKN/Part_II/69
Constant Member Functions(contd.)
• A constant member function can be invoked for
both constant and non-constant objects.
• A non constant member function can be invoked
only for non-constant objects.
Example:
void f(Date &d, const Date& cd){
int i=d.year(); // Ok (one)
int k=d.addYear(1); // Ok (two)
int l=cd.addYear(1); //Error (two)
int m=cd.year(); //Ok(two)
}

70. OOP/AKN/Part_II/70
Static Class Members
Static data member is an attribute that is a
part of class, yet is not a part of an object
In other words there is exactly one copy of a
static member instead of one copy per
object
A Function that needs access to members
of a class, yet does not need to be invoked
for a particular object is called static
member function

71. OOP/AKN/Part_II/71
Example Static data member
class Sclass{
int x, y;
static int z;
. . .
};
int Sclass::z;
main() {
Sclass o, p, q;
}
o
x y
p
x y
q
x y
z

72. OOP/AKN/Part_II/72
Example: Number of objects that are live in
any point of the program
class Employee{
char* name;
static int count; // static data memb.
public:
Employee(char*);
char* getName();
static int getCount(); // static memb. func
~Employee();
};

73. OOP/AKN/Part_II/73
Example (contd)
int Employee::count=0;
int Employee::getCount()
{return count;}
Employee::Employee(char* N){
name=new char[strlen(N)+1];
strcpy(name,N);
++count;
}

74. OOP/AKN/Part_II/74
Example (contd)
Employee::~Employee(){
delete [] name;
--count;
}
char* Employee::getName(){
return name;
}
main(){
cout<<“no of Employees: “<<
Employee::getCount()<<endl;
Employee* e1=new Employee (“Bob”);
Employee* e2=new Employee (“John”);

75. OOP/AKN/Part_II/75
Example (contd)
cout<<“no of employees: “
<<e1->getCount();
cout<<“Emp1: “<<e1->getName();
cout<<“Emp2: “<<e2->getName();
delete e1;
cout<<“no of employees: “
<<e2->getCount();
delete e2;
cout<<“no of employees: “
<<Employee::getCount();
}

76. OOP/AKN/Part_II/76
Static Class Members
 Static data members are accessible by both static
and/or non-static member functions
 Static member functions can only access the static
class members
 To access a public static class member, simply
prefix the class name and scope resolution
operator
 To access a private static class member, when no
object exists take help of a static member function
otherwise non-static could be used.

77. OOP/AKN/Part_II/77
Contents
Operator Overloading
Friend Functions
Data Conversion
Copying Objects
this pointer
Friend class
Nested class
A Complete Example

78. OOP/AKN/Part_II/78
Overloading Operators
 Operator Overloading allows us to overload the
existing operators s.t. they can have operands as
objects
Complex C=A+B;//A & B are complex number objs
 It doesn't provide any means to create new
operators
 Some operators Can‟t be overloaded
 Binary operators may be overloaded either by a
non-static member function having one argument
or a non-member function having two arguments

79. OOP/AKN/Part_II/79
Example: Distance class
class Distance{
int feet;
float inches;
public:
Distance():feet(0),inches(0.0){}
Distance(int f, float i):feet(f),
inches(i){}
void showDistance(){
cout<<feet<<„‟‟<<inches<<„”‟<<endl;}
Distance addDistance(Distance);
};

80. OOP/AKN/Part_II/80
Example (contd.)
Distance Distance::addDistance(Distance d){
Distance res;
res.feet=feet+d.feet;
res.inches=inches+d.inches;
if(res.inches>=12.0){
res.inches-=12.0;
res.feet ++;
}
return res;
}

81. OOP/AKN/Part_II/81
Overloading + Operator
class Distance{
int feet;
float inches;
public:
Distance():feet(0),inches(0.0){}
Distance(int f, float i):feet(f),
inches(i){}
void showDistance();
Distance operator+(Distance);
};

82. OOP/AKN/Part_II/82
Example (contd.)
Distance Distance::operator+(Distance d){
int f=feet+d.feet;
float i=inches+d.inches;
if(i>=12.0){
i-=12.0;
f++;
}
return Distance(f,i);
}

83. OOP/AKN/Part_II/83
Example (contd.)
main(){
Distance d1(10,6), d2(11,7);
Distance d3=d1+d2;
d1.showDistance();
d2.showDistance();
d3.showDistance();
Distance d4=d1+d2+d3;
d4.showDistance();
}
10’ 6”
11’ 7”
22’ 1”
43’ 2”

84. OOP/AKN/Part_II/84
Task
Overlaod + and – operators for ComplexNum
class
Design the class
Define functions
Main function

85. OOP/AKN/Part_II/85
Passing two args: a non member function
class Distance{
int feet;
float inches;
public:
Distance();
Distance(int, float);
void showDistance();
};
Distance operator+(Distance, Distance);

86. OOP/AKN/Part_II/86
Example (contd.)
Distance operator+(Distance d1, Distance
d2){
int f = d1.feet+d2.feet;
float i = d1.inches+d2.inches;
if(i>=12.0){
i-=12.0;
f++;
}
return Distance(f,i);
}
Illegal
Accessing private
data members

87. OOP/AKN/Part_II/87
A solution: with a non member function
class Distance{
int feet;
float inches;
public:
Distance();
Distance(int, float);
void showDistance();
int getFeet(){return feet;}
float getInch(){return inch;}
};
Distance operator+(Distance, Distance);

88. OOP/AKN/Part_II/88
Passing Two Args
Distance operator+(Distance d1, Distance d2){
int f=d1.getFeet()+d2.getFeet();
float i=d1.getInch()+d2.getInch();
if(i>=12.0){
i-=12.0;
f++;
}
return Distance(f,i);
}
Note: In one program, there should be only one
operator overloading function for each operator.
Remember that this
function should be a
non-member!

89. OOP/AKN/Part_II/89
Friend Function
 A friend of a class is a function that is not a member of
the class but is permitted to use the private and
protected members of the class
 The name of the friend is not in the scope of the class
and the friend is not called with the member access
operator
 It can be declared in either private or public part of a
class
 A friend is explicitly declared inside the class
declaration of which it is a friend
 Key word is friend

90. OOP/AKN/Part_II/90
Friend Function
Example
class Sample{
int a;
int b;
public:
Sample(int x,int y):a(x),b(y){}
friend float mean(Sample s){
return float(s.a+s.b)/2.0;
}
};

91. OOP/AKN/Part_II/91
Example (contd.)
main(){
Sample test(13,10);
cout<<“mean is:”<<mean(test);
}
What is the use?
 If it is required to to operate on private
members of two different and unrelated
classes then friend to both classes will help.
 It can be helpful in operator overloading

92. OOP/AKN/Part_II/92
Overloading using friend function
class Distance{
int feet;
float inches;
public:
Distance();
Distance(int, float);
void showDistance();
friend Distance operator+(Distance,
Distance);
};

93. OOP/AKN/Part_II/93
Example (contd.)
Distance operator+(Distance d1, Distance
d1){
int f = d1.feet+d2.feet;
float i = d1.inches+d2.inches;
if(i>=12.0){
i-=12.0;
f++;
}
return Distance(f,i);
}
Legal
Accessing private data
members as it is a friend
function

94. OOP/AKN/Part_II/94
Example (contd.)
main(){
Distance d1(10,6), d2(11,5);
Distance d3=d1+d2;
d1.showDistance();
d2.showDistance();
d3.showDistance();
Distance d4=d1+d2+d3;
d4.showDistance();
}

95. OOP/AKN/Part_II/95
Example
 Matrix Vector product
class Matrix;
class Vector{
float v[4];
…
friend Vector operator* (Matrix &,Vector &);
};
class Matrix{
Vector m[4];
…
friend Vector operator*(Matrix&, Vector&);
};

96. OOP/AKN/Part_II/96
Example (Contd.)
Vector operator *(Matrix& mat, Vector& vec)
{
Vector res;
for(int i=0;i<4;i++){
res.v[i]=0;
for(int j=0;j<4;j++)
res.v[i]+=mat.m[i].v[j]*vec.v[i]; }
return res;
}
//Complete the program and execute

97. OOP/AKN/Part_II/97
Task
Overlaod + and – operators for ComplexNum
class using non-member(friend) functions.
Design the class
Define functions
Main function

98. OOP/AKN/Part_II/98
A Comparison
Access to
private part
Inside
scope of
the class
Invoked with
reference to
an object
Member
function
Yes Yes Yes
Static -
member
Yes Yes Optional
Friend
function
Yes No No

99. OOP/AKN/Part_II/99
Unary Operators
A Unary operator can be defined by either a
member function taking no arguments or a
non-member function taking one argument
Example
class X{
operator ++(); //prefix
operator ++(int); //postfix
}

100. OOP/AKN/Part_II/100
Example (contd.)
The int argument is simply a dummy
argument. It is used to distinguish between a
prefix and postfix application
Example
void operator ++(int){//postfix
feet++;
}
void operator ++(){//prefix
++feet;
}
d1++; d1.showDistance( );
++d2; d2.showDistance( );

101. OOP/AKN/Part_II/101
Mixed mode overloading
How to execute when two operands are of
different type?
Complex c,c1;
double d;
c+=c1; c+=d; c=d+c1; c=c1+d;
Complex operator +=(Complex a){
re+=a.re;
im+=a.im;
return *this;
}
Member
function

102. OOP/AKN/Part_II/102
Overloading(contd.)
Complex operator +=(double a){
re+=a;
return *this;
}
}; //end of class
Complex operator +(double a, Complex
b){
complex r=b;
return r+=a;
}
Non-Member
function
Member
function

103. OOP/AKN/Part_II/103
Overloading(contd.)
Complex operator +(Complex a,
double b){
complex r=a;
return r+=b;
}
Task
Complete the above program with all possible
types of operator overloading with mixed
mode arithmetic.
Non-Member
function

104. OOP/AKN/Part_II/104
Example
main(){
Complex c1, c2;
cin>>c1; cin >>c2;
Complex c3=c1+c2;
cout<<c1<<endl;
cout<<c2<<endl;
Complex c4=c1+c2+c3;
cout<<c4<<endl;
}
Error

105. OOP/AKN/Part_II/105
Overloading Stream Insertion and extraction
operators
class Complex{
…
friend ostream& operator<<(ostream&,
Complex);
friend istream& operator>>(istream&,
Complex&);
};
ostream& operator<<(ostream& out,
Complex c){
out<<c.re<<“ + i”<<c.img<<endl;
return out;}

106. OOP/AKN/Part_II/106
Operator overloading
istream& operator>>(istream& in,
Complex &c){
in>>c.re>>c.img;
return in;
}
 These functions must be non members as
the objects of class Complex appears in
each case as the right operand and the
function can not be a part of class ostream
and istream

107. OOP/AKN/Part_II/107
Data Conversion
 „=„ is a special operator with complex properties.
 When both sides are of equal type, the compiler
does not need any special instructions to operate.
 If they are different ?
Conversion between Basic Types:
(int)=(float); //allowed
 Each such conversion has its own routine, built
into the compiler. This is called an implicit
conversion(casting).

108. OOP/AKN/Part_II/108
Data Conversion (contd.)
 Sometimes we need explicit casting like
float ..= float(int ..)
 This conversion also use the built-in routines
available with the compiler.
 User Defined to Basic Types
float ..=float(Distance);
float f = d1;
Operator float(){
float ft=inches/12;
ft+=float(feet);
return ft;}

109. OOP/AKN/Part_II/109
Data Conversion(contd.)
 Basic to User-defined type
Distance d1=2.35;
Distance(float f){
feet=int(f);
inches=12*(f-feet);
}
 User-defined to User-defined type
objA=objB;//both are objects of
different classes

110. OOP/AKN/Part_II/110
Data Conversion(contd.)
class Rect{
double xco;
double yco;
public:
…
}
class Polar{
double radius;
double angle;
public:
…

111. OOP/AKN/Part_II/111
Data Conversion(contd.)
operator Rect(){
double x=radius*cos(angle);
double y=radius*sin(angle);
return Rect(x,y);
} //inside class declaration
}; //class ends here
main(){
Rect rec; Polar pol(10.0,0.785398);
rec=pol;
pol.display(); rec.display();}

112. OOP/AKN/Part_II/112
Pitfalls/Guidelines of Data Conversion
Use Similar meanings
Use overload operators to perform similar
operations as in basic types
Use Similar Syntax
Don‟t try to create new operators also don‟t design
binary operators for unary action and vice versa
Show Restraint
Don‟t overload operators if not required frequently.
Also Limit the overloaded operators for a class to
manage complexity

113. OOP/AKN/Part_II/113
Pitfalls/Guidelines of Data Conversion
Avoid Ambiguity
Don‟t try to overload the same operator in many
different ways in a same program. This may be a
confusion for the compiler.
Not All operators can be overloaded.
*(pointer), .(access op), :: (scope),
?: (ternary), and sizeof()

114. OOP/AKN/Part_II/114
Copying Objects
class Table{
char *name;
float size;
public:
Table(float s=15){
name=new char[size=s];}
};
1.Table t1;
2.Table t2=t1;
3.Table t3;
4.t3=t2;
5.Table t4(t3);
Default Constructor
//constructor is called
//copy initialization
//constructor is called
//copy assignment
//copy constructor

115. OOP/AKN/Part_II/115
Copying Objects (contd.)
 Line 1: default constructor is called and the
address for the memory allocated is stored in
name variable.
 Line 2: It is initialized by copying. i.e memberwise
copying t2.name=t1.name;
 Now both object point to same memory area.
 Line 3: default constructor is called and the
address for the memory allocated is stored in
name variable.(t3.name)
 Line 4: t3.name is overwritten by t2.name which is
nothing but t1.name
 Line 5: . . .

116. OOP/AKN/Part_II/116
Copying Objects (contd.)
Conclusion:
1. Storage for t3 is lost to program for ever
2. All objects point to same memory area
3. Destructor will be called Four times(?)
i.e. the same memory area will be deleted four
times and the result is undefined( may be
disastrous!)
Also called as shallow copy

117. OOP/AKN/Part_II/117
Copy Constructors
Make a duplicate copy of an object of the
same class, the default make a
memberwise copy of the the object
The default Copy constructors is created by
the compiler automatically.
A local copy of the object is constructed
which may create anomalies.
Copy constructors can also be defined by
us, which can be designed meaning fully
according to the requirement.

118. OOP/AKN/Part_II/118
Copy Constructors(Deep Copy)
class Table{
. . .
Table (const Table&);
Table& operator=(const Table&);
};
Table::Table(const Table& t){
name=new char[size=t.size];
strcpy(name,t.name);
}
Copy constructor
Copy assignment

119. OOP/AKN/Part_II/119
Copy Constructors(contd.)
Table& operator=(const Table& t){
if(this!=&t){
delete name;
name=new char[size=t.size];
strcpy(name,t.name);
}
return *this;
}
 Why copy constructor takes the argument as const and
a reference?

120. OOP/AKN/Part_II/120
The “This” Pointer
Every object has access to its own address
through a pointer called „this‟
The this pointer is passed as an implicit first
argument on every non-static member
function call for an object.
The this pointer is implicitly used to refer both
the data and function members of an object
It can also be used explicitly;
Example: (*this).x=5; or this->x=5;

121. OOP/AKN/Part_II/121
Friend Classes
 If a class is declared as friend to another class then
it is allowed to access all the members of that class
 To declare class A as a friend of class B, place the
corresponding declaration in the definition of class
B.
Example:
class ClassOne{
...
friend ClassTwo;
};
 Friendship is neither symmetric nor transitive.
ClassTwo is allowed to
access all the members of
ClassOne

122. OOP/AKN/Part_II/122
Nested Classes
Classes like blocks and namespaces can be
nested.
These are all scopes and nesting allows local
hiding of names and local allocation of
resources.
This is often the case when a class is
needed as part of the implementation of a
larger construct

123. OOP/AKN/Part_II/123
Nested Classes (Contd.)
char c; //::c
class X{
char c; //X::c
public:
class Y{
char c; //X::Y::c
public:
void foo(char e){
X t; ::c=t.X::c=c=e;}
};
};

124. OOP/AKN/Part_II/124
Local / Global classes
 Class declared out of all scopes are called
global class.
These classes may be used to create
objects anywhere in the program.
Class declared inside a scope (function etc)
are called local class.
Objects of this class can be used inside the
specified scope only.

125. OOP/AKN/Part_II/125
A more complete example
class String{
int length;
char *ptr;
void setString(const char*);
public:
String(const char* = ““);
String(const String&);
~String();
String& operator=(const String&);
String& operator +=(const String &);
bool operator !()const;
bool operator ==(String&)const;

126. OOP/AKN/Part_II/126
Example (contd.)
bool operator <(String)const;
bool operator !=(String&)const;
bool operator >(String&)const;
bool operator <=(String&)const;
bool operator >=(String&)const;
char& operator[](int);
String operator()(int,int);
int getLength()const;
friend ostream& operator<<(ostream&, const
String&);
friend istream& operator>>(istream&,
String&);
}; //end of class def.

127. OOP/AKN/Part_II/127
Example (contd.)
void String::setString(const char *s2){
ptr=new char[length+1];
strcpy(ptr,s2);}
String::String(const char* s){
length=strlen(s);
setString(s);}
String::String(String& copy){
length=copy.length;
setString(copy.ptr);}
String::~String(){delete []ptr;}

128. OOP/AKN/Part_II/128
Example (contd.)
String& String::operator=(String& right){
if(&right!=this){
delete [] ptr; length=right.length;
setString(right.ptr);
}
return *this;
}
String& String::operator+=(String& right){
char *tmp=ptr; length+=right.length;
ptr=new char[length+1]; strcpy(ptr,tmp);
strcat(ptr,right.ptr); delete [] tmp;
return *this;
}

129. OOP/AKN/Part_II/129
Example (contd.)
bool String::operator!()const{
return length==0;}
bool String::operator==(String&
right)const{
return strcmp(ptr,right.ptr)==0;}
bool String::operator<(String
right)const{
return strcmp(ptr,right.ptr)<0;}
bool String::operator!=(String&
right)const{
return !(*this==right);}

130. OOP/AKN/Part_II/130
Example (contd.)
bool String::operator>(const String&
right)const{
return right<*this; }
bool String::operator<=(const String&
right)const{
return !(right<*this); }
bool String::operator>=(const String&
right)const{
return !(*this<right); }

131. OOP/AKN/Part_II/131
Example (contd.)
char& String::operator[](int sbsrpt){
if(sbsrpt>=0 && sbsrpt<length)
return ptr[sbsrpt]; }
String String::operator()(int i,int l){
if(i>=0 && i<length && l>=0 )
int len;
if((l==0)||(i+l>length))
len=length-i;
else
len=l;
char* tmp=new char[len+1];
strncpy(tmp,&ptr[i],len); tmp[len]=„0‟;
String tmpString(tmp); delete[]tmp;
return tmpString;}

132. OOP/AKN/Part_II/132
Example (contd.)
int String::getLength()const{
return length; }
ostream& operator<<(ostream& out,
const String& s){
out<<s.ptr; return out; }
istream& operator>>(istream& in,
String& s){
char tmp[500];
in>>tmp; s=tmp; return in;}

133. OOP/AKN/Part_II/133
Example (contd.)
#include<iostream>
#include<cstring>
main(){
String s1(“Happy”), s2(“birthday”),s;
cout<<(s2==s1?”true”:”false”)<<endl;
cout<<(s2!=s1?”true”:”false”)<<endl;
cout<<(s2>s1?”true”:”false”)<<endl;
cout<<(s2>=s1?”true”:”false”)<<endl;
cout<<(s2<=s1?”true”:”false”)<<endl;
if(!s){cout<<“empty”; s=s1;cout<<s;}

134. OOP/AKN/Part_II/134
Example (contd.)
s1+=s2;
cout<<s1 <<endl;
s1+=“ to you”;
cout<<s1<<endl;
cout<<s1(0,14)<<endl;
String *s4ptr=new String(s1);
cout<<*s4ptr;
S1[0]=„H‟;s1[6]=„B‟;
cout<<s1;
}

135. OOP/AKN/Part_II/135
Task
 Design a class called LargeInt to handle integers
of large size (O(103 ) digits)
 overload all arithmetic operators (+, -, *, /, %)
 overload all unary (++, --, +=, . . .) operators
 overload all relational operators
 design copy constructor and copy assignment
 Member function to test primality
 Write a suitable main function to demonstrate all
above facilities

136. OOP/AKN/Part_II/136
Readings
Programming
 Bjarne Stroustrup, The C++ Programming Language, PE
 Lippman, Lajoie, C++ Primer, Addison-Wesley
 B. Eckel, Thinking in C++, Vol I and Vol II
 Deitel & Deitel, C++ How to program
 Schildt, C++ The complete reference
 S. Sahay, OOP with C++
 E. Balagurusami, Object oriented programming with C++
Concepts
 G.Booch, Object Oriented Analysis & Design
 Bertand Meyer, Object Oriented Software Construction