# HOMEWORK No.3

Course : Object Oriented Programming Code : CSE202

Date of Assignment : Date of Submission :

PART A

Q1. In what order are the class constructors called when a derived class object is created?

If the base class has constructors that are to be called then according to the Syntax shown below:

Derived_class _name():Base_class_name()

We can call the base class constructors as well.Therefore first the base class con-structor is executed and then the derived class constructor is called.

#include<iostream.h>

#include<conio.h>

class A

{

int x;

public:

A(int i)

{

x=i;

cout<<"\nA is initialized";

}

void show_x()

{

cout<<"\nx="<<x;

}

};

class B

{

float y;

public:

B( float j)

{

y=j;

cout<<"\nB is initialized";

}

void show_y()

{

cout<<"\ny="<<y;

}

};

class C:public A,public B

{

int m,n;

public:

C( int a, float b, int c, int d):A(a),B(b)

{

m=c;

n=d;

cout<<" \nC is initialized";

}

void show_z()

{

cout<<"\nm="<<m;

cout<<"\nn="<<n;

}

};

void main()

{

clrscr();

C c(4,5,6,7);

c.show_x();

c.show_y();

c.show_z();

getch();

}

b) Class D is derived from class B. The class D does not contain any data members

of its own. Does the class D require constructors? If yes, why?

If a base class does not have any constructor then derived class need not have a con-structor function. If a base class contains any constructor function with any argu-ment then it is mandatory for the derived class to have a constructor and pass the arguments to the base class constructor when both classes have constructor then base class will execute firstly and then derived class will be executed. 

Q2. We know that a private member of a base class is not inheritable. Is it anyway possible for the objects of a derived class to access the private members of the base class? If yes,how? Remember the base class cannot be modified.ANSWER:

We know that the private members of a class can only be achieved through the member functions of that class.

But this can be accomplish by modifying the visibility mode of the private member by making it public but there will be the disadvantage of this, which is that this would we accessible to all other function of the program, thus taking away the ad-vantage of data hiding.

We know C++ provide a third mode protected. Protected part of class is accessible by member function within its class and any class immediately derived from it.

Thus ,if we want to access the private members of the base class which cannot be in-herited ,we need to call the member function of the base call through the member function the derived class as shown in the example below:

Example: 1

#include<iostream.h>

#include<conio.h>

Class A

{

int a;

public:

void show()

{

a=10;

cout<<”The value of a is”<<a;

}

};

Class B:public A

{

public:

void aces( )

{

A::showdata( );

}

};

void main()

{

clrscr( );

B obj;

obj.aces( );

getch( );

}

Q3. Assume that a publishing company prints books and digital books(electronic form- CD). Create a class named publication with data members title, price, and au-thor’s name. From publication class, derive two classes named book and ebook. Te book class adds a page count data member named pcount while ebook adds data member playing time name ptime.Each of these classes must have member function getdata( ) to read class specific data from keyboard and displaydata( ) to output the class specific data to the computer screen.

#include<iostream.h>

#include<conio.h>

class publication

{

int price;

char n[10];

char t[20];

public:

void getdata()

{

cout<<”enter the name, title and price”;

cin>>n>>t>>p;

}

Void display()

{

cout<<”the name, title and price are”<<n<<t<<p;

}

};

class book:public publication

{

private:

Int  pcount;

public:

void getdata()

{

cout<<”enter the pcount”;

cin>>pcount;

}

void displaydata()

{

display();

cout<<”the pcount is”<<pcount;

}

};

class ebook : public publication

{

private:

int ptime;

public:

void getdata();

{

cout<<”enter the ptime”;

cin>>ptime;

}

void displaydata()

{

cout<<”the ptime is”<<ptime;

}

};

void main()

{

book b;

ebook e;

b.getdata();

e.getdata();

b.displaydata();

e.displaydata();

getch();

} 

PART B

Q4. How is polymorphism achieved at (a) compile time (b) run time?

(b) How does the concept of virtual function help in achieving polymorphism?Illustrate your answer by giving a suitable example.

(a) Function Overloading and Operator Overloading

The overloaded functions are selected for invoking by matching arguments. This is known to compiler at the compile time and therefore compiler is able to select the appropriate function for a particular call at the compile time itself which is called early binding or static binding. 

(a) Consider the following example

Ex.          

class A

{

int x;

public:

void show()

};

class B:public A

{

int y;

public:

void show();

};

since the function show() is same in both the classes therefore static binding does not apply. Therefore member function could be selected while the program is run-ning.

(b)

When we use the same function name in both the base class and derived class, the function in base class is declared as virtual using the keyword virtual. When the function is made virtual then C++ determines which function is to use at runtime, based on the type of object pointed to by the base pointer. Thus by making the base pointer to point different objects we use different versions of virtual functions. 

#include<iostream.h>

#include<conio.h>

class Base

{

public:

virtual void getdata()=0;

};

class Drive:public Base

{

public:

void getdata()

{

cout<<"\nDrive class";

}

void showdata()

{

cout<<"\nDisplay derive";

}

};

void main()

{

clrscr();

Drive d;

Drive *p;

p=&d;

p->getdata();

p->showdata();

getch();

Q5. When do we make a virtual function “pure”? What are the implications of making a

function a pure virtual function?

ANS 5

We make the virtual function pure because compiler requires the each derived class to either define the function or redeclare it as a pure virtual function. A class con-taining the pure virtual function cannot use to declare the object of its own. 

Example :

#include<iostream.h>

#include<conio.h>

class Base

{

public:

virtual void getdata()=0;

};

class Drive:public Base

{

public:

void getdata()

{

cout<<"\nDrive class";

}

void showdata()

{

cout<<"\nDisplay derive";

}

};

void main()

{

clrscr();

Drive d;

Drive *p;

p=&d;

p->getdata();

p->showdata();

getch();

}

Q6. Develop an object oriented program in C++ to read the following information from the keyword in which the base class consists of employee name, code and designation, and the derived class containing the data members, viz. years of experience and age.

a) Employee nameb) Employee codec) Designationd) Years of experiencee) Age

ual base class for the item employee name and code.

Design a virt Design a virtual base class for the item employee name and code.

ANS 6

#include<iostream.h>

#include<conio.h>

Class A

{

int emp_code;

char emp_name[10];

char desig;

public:

void getdata()

{

cout<<”enter the name , code and designation”;

cin>>n

cin>>c

cin>>d;

}

void display()

{

cout<<”the name ,code and designation is”<<n<<c<<d;

}

};

Class B: virtual public A

{

int a;

int y;

public:

void getdata()

{

A::getdata();

cout<<”enter the age and years of experience”;

cin>>a

cin>>y;

}

void display1()

{

A::display();

cout<<”the age and years of experience are”<<a<<y;

}

};

void main()

{

B obj;

Obj.getdata1();

Obj.display1();

getch();

}