Inheritance : Extending Classes

Inheritance : Extending classesInheritance : Extending classes
By
Nilesh Dalvi
Lecturer, Patkar-Varde College.Lecturer, Patkar-Varde College.
http://www.slideshare.net/nileshdalvi01
Object oriented ProgrammingObject oriented Programming
with C++with C++

Introduction
• Inheritance is one of the most useful and
essential characteristics of oops.
• Existing classes are main components of
inheritance.
• New classes are created from existing one.
• Properties of existing classes are simply
extended to the new classes.
• New classes are called as derived classes
and existing one are base classes.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

Introduction
Fig. Inheritance

Types of Inheritance
1. Single Inheritance
2. Multiple Inheritance
3. Hierarchical Inheritance
4. Multilevel Inheritance
5. Hybrid Inheritance

Single inheritance:
A derived class with only one base class is
called as single inheritance.

Multiple inheritance:
A derived class with several base classes is
called as Multiple inheritance.

Multilevel inheritance:
The mechanism of deriving a class from
another ‘derived class’ is known as multilevel
inheritance.

Hierarchical inheritance:
One class may be inherited by more than one
class. This process is known as hierarchical
inheritance.

Hybrid inheritance:
It is combination of Hierarchical and Multilevel
inheritance.

Defining derived class
• A derived class can be defined by specifying its
relationship with the base class in addition to its
own details.
class derived-class-name : visibility-mode base-class-name
{
//members of derived class.
};
• The colon (:) indicates that derived-class-name is
derived from the base-class-name.
• The visibility-mode is optional and if present may be
either private or public. The default visibility-mode
is private

• Visibility-mode specifies whether the features of the base
class are privately derived or publicly derived.
• For Example:
Defining derived class
class base
{
private:
public:
//members of base class
}
class derived : private base
{
}
class derived : public base
{
}
class derived : base
{
}

• public members of the base class become
private members of the derived class.
• Therefore, the public members of the base
class can only be accessed by the member
functions of the derived class.
• They are not accessible to the object of the
derived class.
Privately Inherited

Privately Inherited
#include <iostream>
using namespace std;
//Public Derivation
class A //Base class
{
public:
int x;
};
class B : private A // Derived class
{
public:
int y;
B()
{
x = 10;
y = 20;
}
void show ()
{
cout << "X : " << x <<endl;
cout << "Y : " << y <<endl;
}
};
int main()
{
B b;
b.show ();
return 0;
}
The object b of derived class
cannot directly access the
variable x.
b.x = 10; // cannot access
class B is privately inherited.
Hence, its access is
restricted.
The object b of derived class
cannot directly access the
variable x.
b.x = 10; // cannot access
class B is privately inherited.
Hence, its access is
restricted.

• public members of the base class remains
public member in derived class.
• Therefore, they are accessible to the objects
of the derived class.
• In both cases, the private members are not
inherited and therefore, the private
members of base class will never become
the members of its derived class.
Publicly Inherited

Publicly Inherited
#include <iostream>
//Public Derivation
class A //Base class
{
public:
int x;
};
class B : public A // Derived class
{
public:
int y;
};
int main()
{
B b;
b.x = 10;
b.y = 20;
cout << "Member of A :" << b.x <<endl;
cout << "Member of B :" << b.y <<endl;
return 0;
}
In main() function, b is an
object of class B. The object
b can access the members
of class A as well as of B
through the statements:
b.x = 10;
b.y = 20;
In main() function, b is an
object of class B. The object
b can access the members
of class A as well as of B
through the statements:
b.x = 10;
b.y = 20;

Privately Inherited
#include<iostream>
class geometry
{
int length;
int breadth;
public:
void get()
{
cout << "Enter values: "<<endl;
cin >> length >> breadth;
}
int area();
};
int geometry :: area ()
{
return length * breadth;
}

Privately Inherited
class Rect : private geometry
{
int height;
public:
void getHeight (int h)
{
get();
height = h;
}
void volume();
};
void Rect ::volume()
{
cout << "Area is: " << area ()<< endl;
cout <<"Volume is : "<< area() * height;
}

Privately Inherited
int main()
{
Rect r;
r.getHeight (2);
//r.area();
r.volume();
return 0;
}
Output:
Enter values:
2
3
Area is: 6
Volume is: 12

• The member functions of derived class cannot
access the private member variables of base class.
• The private members of base class can be accessed
using public member functions of the same class.
• This approach makes a program lengthy.
• To overcome the problem associated with private
data, the creator of C++ introduced another access
specifier called protected.
• protected is same as private , but it allows the
derived class to access the private members
directly.
Protected data with private inheritance

class ABC
{
private: // optional
.... //visible to member functions within class
protected: //visible to member functions of its own
.... // and of its derived class
public: //visible to all functions in the program
.... //
};

#include <iostream>
// PROTECTED DATA //
class A // BASE CLASS
{
protected: // protected declaration
int x;
};
class B : private A // DERIVED CLASS
{
int y;
public:
B ()
{
x = 30;
y = 40;
}
void show()
{
cout <<"n x = "<<x;
cout <<"n y = "<<y;
}
};

int main()
{
B b; // DECLARATION OF OBJECT
b.show();
return 0;
}
Output :
x = 30
y = 40

Access specifies with scopes
Sr.
No. Base class
access mode
Derived class access mode
private
derivation
public
derivation
protected
derivation
A public private public protected
B private Not inherited Not inherited Not inherited
C protected private protected protected

Access controls of functions
Sr.
No Types of functions Access mode
private public protected
A. Class member function √ √ √
B. Derived class member x √ √
C. Friend function √ √ √
D. Friend class member √ √ √

Single Inheritance
class ABC
{
protected:
char name [20];
int age;
};
class abc : public ABC // public derivation
{
float height;
float weight;
public:
void getdata()
{
cout << "nEnter name and age: " ;
cin >>name>>age;
cout << "nEnter height and weight: " << endl;
cin >>height>>weight;
}
void show ()
{
cout << "nName :" <<name<< "nAge :" <<age;
cout << "nHeight :" <<height << "nWeight :" <<weight;
}
};

int main()
{
abc x;
x.getdata(); // reads data through keyboard
x.show(); // displays data on the screen
return 0;
}
Single Inheritance
class ABC has two protected
data members name and age.
class abc with two data
members inherit class ABC
publically. In main function, x
is an object of derived class
invokes member function
getdata() and show().
class ABC has two protected
data members name and age.
class abc with two data
members inherit class ABC
publically. In main function, x
is an object of derived class
invokes member function
getdata() and show().

Multilevel Inheritance
#include<iostream>
class top //base class
{
protected:
int a;
public :
void getdata()
{
cout<<"nnEnter first Number ::t";
cin>>a;
putdata();
}
void putdata()
{
cout<<"nFirst Number is ::t"<<a;
}
};

//First level inheritance
class middle :public top // class middle is derived_1
{
protected:
int b;
public:
void square()
{
getdata();
b=a*a;
cout<<"nnSquare is ::t"<<b;
}
};

//Second level inheritance
class bottom :public middle // class bottom is derived_2
{
int c;
public:
void cube()
{
square();
c=b*a;
cout<<"nnCube is ::t"<<c;
}
};
int main()
{
bottom b1;
b1.cube();
return 0;
}
Output :
Enter first Number :: 2
First Number is :: 2
Square is :: 4
Cube is :: 8

• When a class is derived from more than one class
then this type of inheritance is called multiple
inheritance.
• Multiple inheritance allows us to combine the
features of several existing classes as a starting
point for deriving new classes.
• Syntax:
class D : visibility-mode B, visibility-mode A
{
//members of D.
};
Multiple Inheritance

#include<iostream>
class M
{
protected:
int m;
public:
void get_m(int);
};
class N
{
protected:
int n;
public:
void get_n(int);
};
class P: public M, public N
{
public:
void display();
};
void M :: get_m(int x)
{
m = x;
}
void N :: get_n(int y)
{
n = y;
}
void P :: display()
{
cout << "M = "<< m << endl;
cout << "N = "<< n << endl;
cout << "M*N = "<< m*n << endl;
}
int main()
{
P x;
x.get_m(10);
x.get_n(20);
x.display();
return 0;
}

For example: A class Rectangle is derived
from base classes Area and Perimeter.

#include <iostream>
class Area
{
public:
float area_calc(float l,float b)
{
return l*b;
}
};
class Perimeter
{
public:
float peri_calc(float l,float b)
{
return 2*(l+b);
}
};

/* Rectangle class is derived from classes Area and Perimeter. */
class Rectangle : private Area, private Perimeter
{
private:
float length, breadth;
public:
Rectangle() : length(0.0), breadth(0.0) { }
void get_data( )
{
cout<<"Enter length: ";
cin>>length;
cout<<"Enter breadth: ";
cin>>breadth;
}
float area_calc()
{
/* Calls area_calc() of class Area and returns it. */
return Area::area_calc(length,breadth);
}
float peri_calc()
{
/* Calls peri_calc() function of class
Perimeter and returns it. */
return Perimeter::peri_calc(length,breadth);
}
};

int main()
{
Rectangle r;
r.get_data();
cout<<"Area = "<<r.area_calc();
cout<<"nPerimeter = "<<r.peri_calc();
return 0;
}
Output:
Enter length: 5.1
Enter breadth: 2.3
Area = 11.73
Perimeter = 14.8

Ambiguity Resolution in Inheritance
class M
{
public:
void display()
{
cout << "class M" << endl;
}
};
class N
{
public:
void display()
{
cout << "class N" << endl;
}
};
class P: public M, public N
{
public:
void display()
{
M :: display();
N :: display();
}
};
int main()
{
P x;
x.display();
return 0;
}
When a function
name with the same
name appears in
more than one base
class, which function
is used by the derived
class when we inherit
these two classes??
When a function
name with the same
name appears in
more than one base
class, which function
is used by the derived
class when we inherit
these two classes??

Hierarchical Inheritance
• One class may be inherited by more than
one classes.
• Hierarchical unit shows top down style
through splitting a compound class into
several simple subclasses.

#include<iostream>
class Polygon
{
protected:
int width, height;
public:
void input(int x, int y)
{
width = x;
height = y;
}
};
class Rectangle : public Polygon
{
public:
int areaR()
{
return (width * height);
}
};

class Triangle : public Polygon
{
public:
int areaT()
{
return (width * height)/2;
}
};
int main()
{
Rectangle r;
r.input(6, 8);
cout << "Area of Rectangle ::" <<r.areaR() <<endl;
Triangle t;
t.input(6, 10);
cout << "Area of Triangle ::" <<r.areaT() <<endl;
return 0;
}

Hybrid Inheritance
• Combination of one or more types of inheritance.
• In fig., GAME is derived from two base classes i.e.
LOCATION and PHYSIQUE.
• Class PHYSIQUE is also derived from class
PLAYER.

Hybrid Inheritance
#include<iostream>
class Player
{
protected:
char name [15];
char gender;
int age;
};
class Physique : public Player
{
protected:
float height;
float weight;
};

Hybrid Inheritance
class Location
{
protected:
char city [10];
char pin [10];
};
class Game : public Physique, public Player
{
protected:
char game [15];
public:
void getdata();
void show();
};
int main()
{
Game g;
g.getdata();
g.show();
return 0;
}

• When a class is derived from two or more classes, which
are derived from the same base class such type of
inheritance is known as multipath inheritance.
• Multipath inheritance consists multiple, multilevel and
hierarchical as shown in Figure.
Multipath Inheritance

• There is an ambiguity problem. When you run
program with such type inheritance. It gives a
compile time error [Ambiguity].
Problem in Multipath Inheritance

• To overcome the ambiguity occurred due to
multipath inheritance, C++ provides the keyword
virtual.
• The keyword virtual declares the specified
classes virtual.
• When classes are declared as virtual, the
compiler takes necessary precaution to avoid
duplication of member variables.
• Thus, we make a class virtual if it is a base
class that has been used by more than one derived
class as their base class.
Virtual base classes

#include<iostream>
class student
{
protected:
int rno;
public:
void getnumber()
{
cout<<"Enter Roll No:";
cin>>rno;
}
void putnumber()
{
cout<<"nntRoll No:"<<rno<<"n";
}
};

class test:virtual public student
{
protected:
int part1,part2;
public:
void getmarks()
{
cout<<"Enter Marksn";
cout<<"Part1:";
cin>>part1;
cout<<"Part2:";
cin>>part2;
}
void putmarks()
{
cout<<"tMarks Obtainedn";
cout<<"ntPart1:"<<part1;
cout<<"ntPart2:"<<part2;
}
};

class sports:public virtual student
{
protected:
int score;
public:
void getscore()
{
cout<<"Enter Sports Score:";
cin>>score;
}
void putscore()
{
cout<<"ntSports Score is:"<<score;
}
};

class result:public test,public sports
{
int total;
public:
void display()
{
total=part1+part2+score;
putnumber();
putmarks();
putscore();
cout<<"ntTotal Score:"<<total;
}
};

int main()
{
result r;
r.getnumber();
r.getmarks();
r.getscore();
r.display();
return 0;
}
Output:
Enter Roll No:111
Enter Marks
Part1:11
Part2:22
Enter Sports Score:33
Roll No:111
Marks Obtained
Part1:11
Part2:22
Sports Score is:33
Total Score:66

Problem statement:
 Define a multipath inheritance structure in which
the class master deserves information from both
account and admin classes which in turn derive
information from the class person.
 Define all four classes and write a program to
create, update, and display the information
contained in master objects.

#include<iostream>
class person
{
protected:
char name[20];
int code;
public:
void getcode()
{
cout<<"n Enter the code ";
cin>>code;
}
void getname()
{
cout<<"n Enter the name ";
cin>>name;
}
};

class account:virtual public person
{
protected:
int pay;
public:
void getpay()
{
cout<<"n Enter the payment ";
cin>>pay;
}
};
class admin:virtual public person
{
protected:
int exp;
public:
void getexp()
{
cout<<"n Enter the experiance ";
cin>>exp;
}
};

class master:public account,public admin
{
public:
void getdata()
{
getcode();
getname();
getpay();
getexp();
}
void update()
{
int c;
cout<<"n You want 2 updaten1.coden
2.namen3.paymentn4.experiance";
cout<<"nEnter ur choice ";
cin>>c;
switch(c)
{
case 1: getcode();
break;
case 2: getname();
break;
case 3: getpay();
break;
case 4: getexp();
break;
default:
cout<<"n Invalid choice";
}
}

void putdata()
{
system("cls");
cout<<"nDetails";
cout<<"n Code "<<code<<"n Name "<<name;
cout<<"n Payment "<<pay<<"n Experiance "<<exp;
cout<<"nPress any key 2 continue ";
getchar();
}
};
int main()
{
int ch;
master m;
while(1)
{
cout<<"nMENUn1.Createn2.Updaten3.Displayn4.Exit";
cout<<"nEnter ur choice ";
cin>>ch;
switch(ch)
{
case 1: m.getdata();
break;
case 2: m.update();
break;
case 3: m.putdata();
break;
case 4: exit(0);
default:cout<<"n Invalid choice";
}
}
return 0;
}

Abstract classes
• An abstract class is one that is not used to
create objects.
• An abstract class is designed only to act as
a base class(to be inherited by other
classes).

• Constructors play an important role in initializing
objects.
• As long as no base class constructor takes any
arguments, the derived class need not have a
constructor function.
• However, if any base class contains a constructor
with one or more arguments, then it is mandatory
for the derived class to have a constructor and
pass arguments to the base class constructor.
• In inheritance we make a objects of derived class.
Thus it make sense to pass arguments to the base
class constructor.
Constructors in Derived classes

• When both derived and base classes contain
constructors, the base class constructor is
executed first and then the constructor in the
derived class is executed.
• In multiple inheritance, the base classes are
constructed in the order in which they appear
in the declaration of the derived class.
• Similarly in multilevel inheritance, the
constructors will be executed in the order of
inheritance.
Constructors in derived class

• The general form of defining the Derived
constructor is :
Derived-constructor(arg1, arg2,..,argN) : base-class1(arg1),..,base-
classN(argN)
{
//body of constructor of derived class.
};
Derived-constructor(arg1, arg2,..,argN) : base-class1(arg1),..,base-
classN(argN)
{
//body of constructor of derived class.
};

Constructors and Destructor in inheritance
Base-class
Constructor
Base-class
Constructor
Derived-class
constructor1
Derived-class
constructor1
Derived-class
constructorN
Derived-class
constructorN
Derived-class
DestructorN
Derived-class
DestructorN
Derived-class
Destructor1
Derived-class
Destructor1
Base-class
DestructorN
Base-class
DestructorN

class alpha
{
private:
int x;
public:
alpha(int i)
{
x = i;
cout << "n alpha initialized n";
}
void show_x()
{
cout << "n x = "<<x;
}
};

class beta
{
private:
float y;
public:
beta(float j)
{
y = j;
cout << "n beta initialized n";
}
void show_y()
{
cout << "n y = "<<y;
}
};

class gamma : public beta, public alpha
{
private:
int n,m;
public:
gamma(int a, float b, int c, int d): alpha(a), beta(b)
{
m = c;
n = d;
cout << "n gamma initialized n";
}
void show_mn()
{
cout << "n m = "<<m;
cout << "n n = "<<n;
}
};

int main()
{
gamma g(5, 7.65, 30, 100);
cout << "n";
g.show_x();
g.show_y();
g.show_mn();
return 0;
}
Output:
beta initialized
alpha initialized
gamma initialized
x = 5
y = 7.65
m = 30
n = 100

• The most frequent use of inheritance is for
deriving classes using existing classes, which
provides reusability. The existing classes
remains unchanged. By reusability, the
development time of software is reduced.
• The derived classes extend the properties of
base classes to generate more dominant object.
• The same base class can be used by a number of
derived classes in class hierarchy.
• When a class is derived from more than one
class, all the derived classes have the same
properties as that of base classes.
Advantages of Inheritance

• The increased time/effort it takes the program to
jump through all the levels of overloaded classes.
– If a given class has ten levels of abstraction above it, then
it will essentially take ten jumps to run through a
function defined in each of those classes
• Two classes (base and inherited class) get tightly
coupled.
– This means one cannot be used independent of each
other.
• Also with time, during maintenance adding new
features both base as well as derived classes are
required to be changed.
– If a method signature is changed then we will be affected
in both cases (inheritance & composition)
Disadvantages of Inheritance

• If a method is deleted in the "super class" or
aggregate, then we will have to re-factor in case
of using that method.
• Here things can get a bit complicated in case of
inheritance because our programs will still
compile, but the methods of the subclass will
no longer be overriding superclass methods.
These methods will become independent
methods in their own right.
Disadvantages of Inheritance

To beTo be
continued…..continued…..

Inheritance : Extending Classes

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