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MC0066 – OOPS using C++ Roll No. XXXXXXXXX

Winter 2011

Master of Computer Application (MCA) – Semester 2MC0066 – OOPS using C++ – 4 Credits

(Book ID: B0681 & B0715)Assignment Set – 1 (40 Marks)

Answer all Questions Each Question carries TEN Marks

Book ID: B 0681

1. With the help of suitable programming examples, explain Selection control

statements and Iteration statements in C++.

Ans:

Selection control statements in C++

There are basically two types of control statements in C++ which allows the programmer tomodify the regular sequential execution of statements. They are selection and iteration

statements. The selection statements allow to choose a set of statements for execution depending

on a condition. If statement and switch statement are two statements which allow selection inC++. There is also an operator known as conditional operator which enables selection.

If statement

Syntax : if (expression or condition)

{ statement 1;

statement 2;

}

else

{ statement 3;

statement 4;

}

The expression or condition is any expression built using relational operators which either yields

true or false condition. If no relational operators are used for comparison, then the expression

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will be evaluated and zero is taken as false and non-zero value is taken as true. If the condition is

true, statement1 and statement2 is executed otherwise statement 3 and statement 4 is executed.

Else part in the if statement is optional. If there is no else part, then the next statement after the if

statement is executed, if the condition is false. If there is only one statement to be executed in the

if part or in the else part, braces can be omitted.

Following example program implements the if statement.

// evenodd.cpp

# include <iostream.h>

# include <conio.h>

void main()

{

int num;

cout<<”Please enter a number”<<endl;

cin>>num;

if ((num%2) == 0)

cout<<num <<” is a even number”;

else

cout<<num <<” is a odd number”;

getch();

}

The above program accepts a number from the user and divides it by 2 and if the remainder

(remainder is obtained by modulus operator) is zero, it displays the number is even, otherwise as

odd. We make use of the relational operator == to compare whether remainder is equal to zero ornot.

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Switch statement

Nested ifs can be confusing if the if statement is deeply nested. One alternative to nested if is the

switch statement which can be used to increase clarity in case of checking the different values of the same variable and execute statements accordingly.

Syntax :

Switch (variablename)

{

case value1: statement1;

break;


break;


break;

default: statement4;

}

If the variable in the switch statement is equal to value1 then statement1 is executed, if it is equalto value2 then statement2 is executed, if it is value3 then statement3 is executed. If the variable

value is not in any of the cases listed then the default case statement or statement4 is executed.The default case specification is optional, however keeping it is a good practice. It can also be

used for displaying any error message. Each case can have any number of statements. Howeverevery case should have a break statement as the last statement. Break statement takes the control

out of the switch statement. The absence of the break statement can cause execution of

statements in the next case. No break is necessary for the last case. In the above example, defaultcase does not contain a break statement.

The following program implements the switch statement

position.cpp

# include<iostream.h>

void main()

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{ char pos;

int x=15, y=15;

cout << “ you are currently located at” <<x<<” “<<y<<endl;

cout>>”please choose the letter to move l for left, r for right, u for up and d for down” <<endl;

cin>>pos;

switch (pos)

{ case ‘l’: x–;

break;

case ‘r’: x++;

break;

case ‘u’: y++;

break;

case ‘d’: y–;

break;

default: cout<<”You selected a wrong option”;

}

cout<<“ you are now located at” <<x<<” “<<y;

}

Conditional Operator

Conditional operator (?:) is a handy operator which acts like a shortcut for if else statement. If you had to compare two variables a and b and then depending on which is larger, you wanted to

store that variable in another variable called large. You would do this using if else statement in

the following way:

if (a>b)

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large=a;

else

large=b;

The above can be done using conditional operator in the following way:

large= (a>b) ? a : b ;

Iteration statements in C++

Iteration or loops are important statements in C++ which helps to accomplish repeatitiveexecution of programming statements. There are three loop statements in C++ : while loop, do

while loop and for loop

While loop

Syntax: while (condition expression)

{

Statement1;

Statement 2;

}

In the above example, condition expression is evaluated and if the condition is true, then the

statement1 and statement2 are executed. After execution, the condition is checked again. If true,

the statements inside the while loop are executed again. This continues until the loop condition

becomes false. Hence the variable used in the loop condition should be modified inside the loopso that the loop termination condition is reached. Otherwise the loop will be executed infinitely

and the program will hang when executed. Also the loop variable should be iniatialised to avoid

the variable taking junk value and create bugs in the program.

The following program implements the while loop

// average1.cpp


void main()

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{

int n=0,a;

int sum=0;

cout<< “enter five numbers”;

while (n<5)

{

cin>>a;

sum=sum+a;

n++;

}

cout<<”Average of the numbers is”<<(sum/n);

}

The above program accepts five numbers from the user and finds the average of the five

numbers. In the above while loop, the variable n is initialized to zero and this variable keeps

track of the count of numbers input from the user. It is incremented every time a number is input

from the user. The number accepted from the user is added to the value stored in the sumvariable. When n becomes 5 the while loop condition becomes false and the average of the

numbers is printed. Please note that there is no semicolon after while and condition expression.

Do..while loop

The do while loop is same as while loop except that the condition is checked after the execution

of statements in the do..while loop. Hence in do..while loop, statements inside the loop are

executed at least once. However, in while loop, since the condition is checked before, thestatements inside the loop will not be executed if the loop condition is false.

Syntax:

do

{

Statement1;

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Statement2

} while (condition expression);

In the above example the statement1 and statement2 are executed and the condition is checked. If

the condition is true then the statements are executed again and if the condition is false then thecontrol is transferred to the next statement after the do..while statement.

Please note that there is no semicolon after do, but there is a semicolon after the conditionexpression in while part. The average1.cpp program is rewritten using do..while loop as follows

// average2.cpp


void main()

{

int n=0,a;

int sum=0;

cout<< “enter five numbers”;

do

{

cin>>a;

sum=sum+a;

n++;

}while (n<5);

cout<<”Average of the numbers is”<<(sum/n);

}

The decision on whether to use while or do..while statement depends on whether the statementsinside the loop have to be executed atleast once or not. If it has to be executed atleast once, then

the do..while statement should be used.

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For loop

The for loop is one of the popular control statement as it is compact and clear in specification.

The loop initialization, loop termination condition statement and statement for the next iterationare all included in one statement.

Syntax:

for(initialization statement; loop termination condition; statement to increment/decrement theloop variable)

{

Statement1;

Statement2;

}

In the above example, initiation statement is executed first and then the termination is checked. If the condition is true, statement1 and statement2 will be executed. Then the third statement in the

for loop is executed which modifies the loop control variable.

Please note that there is no semicolon after the for statement.

The following program demonstrates the use of for loop to find the factorial of a number.

// factorial.cpp


void main()

{

int number,fact=1;

cout<< “enter a number”;

cin>>number;

for(int i=number;i>1;i–)

fact=fact*i;

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cout<<”Factorial of <<number<<“is”<<fact;

}

2. Write your own C++ functions for the following problems:

Sort a book list in a library based on the discipline

Print the sorted output on the console

Ans:

#include <iostream>

#include <string>

#include <vector>

#include <iterator>

#include <algorithm>

using namespace std;

class CBook {

private:

string strTitle;

string strAuthor;

string strDiscipline;

public:CBook(const string& strPTitle, const string& strPAuthor, const string& strPDiscipline) :

strTitle(strPTitle), strAuthor(strPAuthor), strDiscipline(strPDiscipline)

{

}

const string& get_title() const {return strTitle;}

const string& get_author() const {return strAuthor;}

const string& get_discipline() const {return strDiscipline;}

static bool compare_disciplineDSC( const CBook& s1, const CBook& s2 ) {

return s1 . get_discipline() . compare(s2 . get_discipline()) > 0 ? true : false;

}

static bool compare_disciplineASC( const CBook& s1, const CBook& s2) {

return s1 . get_discipline() . compare(s2 . get_discipline() ) < 0 ? true : false;

}

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friend int sort_discipline(const CBook &a, const CBook &b)

{

return a.strDiscipline.compare(b.strDiscipline) < 0 ? 1 : 0;

}

friend ostream& operator<<(ostream& os, const CBook& book)

{

os << "\n Title: " << book.strTitle <<

"\n Author: " << book.strAuthor <<

"\nDiscipline: " << book.strDiscipline;

return os;

}

};

class CBookList : public vector<CBook>

{public:

friend ostream& operator<<(ostream& os, const CBookList& bl)

{

copy(bl.begin(), bl.end(), ostream_iterator<CBook>(os, "\n"));

return os;

}

};

int main()

{CBookList a;

string strA[3];

a.clear();

for (int i = 0; i < 10; i++) {

strA[0] = " Title"; strA[0] += 'A' + i;

strA[1] = " Author"; strA[1] += 'A' + i;

strA[2] = "Discipline"; strA[2] += 'A' + i;

a.push_back(CBook(strA[0], strA[1], strA[2]));

}

cout << "Creation Order\n" << a << endl;

sort(a.begin(), a.end(), CBook::compare_disciplineDSC);

cout << "\nSorted descending\n" << a << endl;

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return 0;

}

OutPut:

Creation Order

Title: TitleA

Author: AuthorA

Discipline: DisciplineA

Title: TitleB

Author: AuthorB

Discipline: DisciplineB

Title: TitleC

Author: AuthorC

Discipline: DisciplineC

Title: TitleD

Author: AuthorD

Discipline: DisciplineD

Title: TitleE

Author: AuthorE

Discipline: DisciplineE

Title: TitleF

Author: AuthorF

Discipline: DisciplineF

Title: TitleG

Author: AuthorG

Discipline: DisciplineG

Title: TitleH

Author: AuthorH

Discipline: DisciplineH

Title: TitleI

Author: AuthorI

Discipline: DisciplineI

Title: TitleJ

Author: AuthorJ

Discipline: DisciplineJ

Sorted descending

Title: TitleJ

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Author: AuthorJ

Discipline: DisciplineJ

Title: TitleI

Author: AuthorI

Discipline: DisciplineI

Title: TitleH

Author: AuthorH

Discipline: DisciplineH

Title: TitleG

Author: AuthorG

Discipline: DisciplineG

Title: TitleF

Author: AuthorF

Discipline: DisciplineF

Title: TitleE

Author: AuthorEDiscipline: DisciplineE

Title: TitleD

Author: AuthorD

Discipline: DisciplineD

Title: TitleC

Author: AuthorC

Discipline: DisciplineC

Title: TitleB

Author: AuthorB

Discipline: DisciplineB

Title: TitleA

Author: AuthorA

Discipline: DisciplineA

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Book ID: B0715

3. Explain the concepts and applications of multiple inheritance and virtual

functions in C++.

Ans:

Multiple Inheritance

We can derive a class from any number of base classes. Deriving a class from more than one

direct base class is called multiple inheritance.

In the following example, classes A, B, and C are direct base classes for the derived class X:

class A { /* … */ };

class B { /* … */ };

class C { /* … */ };

class X : public A, private B, public C { /* … */ };

The following inheritance graph describes the inheritance relationships of the above example. Anarrow points to the direct base class of the class at the tail of the arrow:

The order of derivation is relevant only to determine the order of default initialization by

constructors and cleanup by destructors.

A direct base class cannot appear in the base list of a derived class more than once:

class B1 { /* … */ }; // direct base class

class D : public B1, private B1 { /* … */ }; // error

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However, a derived class can inherit an indirect base class more than once, as shown in the

following example:

class L { /* … */ }; // indirect base class

class B2 : public L { /* … */ };

class B3 : public L { /* … */ };

class D : public B2, public B3 { /* … */ }; // valid

In the above example, class D inherits the indirect base class L once through class B2 and once

through class B3. However, this may lead to ambiguities because two subobjects of class L exist,

and both are accessible through class D. We can avoid this ambiguity by referring to class L usinga qualified class name. For example:

B2::L

or

B3::L.

We can also avoid this ambiguity by using the base specifier virtual to declare a base class.

Virtual Functions

By default, C++ matches a function call with the correct function definition at compile time. This

is called static binding. We can specify that the compiler match a function call with the correct

function definition at run time; this is called dynamic binding. We declare a function with the

keyword virtual if we want the compiler to use dynamic binding for that specific function.

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A virtual function is a member function we may redefine for other derived classes, and can

ensure that the compiler will call the redefined virtual function for an object of the correspondingderived class, even if we call that function with a pointer or reference to a base class of the

object.

A class that declares or inherits a virtual function is called a polymorphic class.

We redefine a virtual member function, like any member function, in any derived class. Suppose

we declare a virtual function named f in a class A, and we derive directly or indirectly from A a

class named B. If we declare a function named f in class B with the same name and same

parameter list as A::f, then B::f is also virtual (regardless whether or not we declare B::f with

the virtual keyword) and it overrides A::f. However, if the parameter lists of A::f and B::f

are different, A::f and B::f are considered different, B::f does not override A::f, and B::f is

not virtual (unless we have declared it with the virtual keyword). Instead B::f hides A::f. The

following example demonstrates this:

#include <iostream>

using namespace std;

struct A {

virtual void f() { cout << "Class A" << endl; }

};

struct B: A {

void f(int) { cout << "Class B" << endl; }

};

struct C: B {

void f() { cout << "Class C" << endl; }

};

int main() {

B b; C c;

A* pa1 = &b;

A* pa2 = &c;

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// b.f();

pa1->f();

pa2->f();

}

The following is the output of the above example:

Class A

Class C

The function B::f is not virtual. It hides A::f. Thus the compiler will not allow the function call

b.f(). The function C::f is virtual; it overrides A::f even though A::f is not visible in C.

If we declare a base class destructor as virtual, a derived class destructor will override that base

class destructor, even though destructors are not inherited.

The return type of an overriding virtual function may differ from the return type of the

overridden virtual function. This overriding function would then be called a covariant virtual

function. Suppose that B::f overrides the virtual function A::f. The return types of A::f and

B::f may differ if all the following conditions are met:

· The function B::f returns a reference or pointer to a class of type T, and A::f returns a pointer

or a reference to an unambiguous direct or indirect base class of T.

· The const or volatile qualification of the pointer or reference returned by B::f has the same or

less const or volatile qualification of the pointer or reference returned by A::f.

· The return type of B::f must be complete at the point of declaration of B::f, or it can be of

type B.

A virtual function cannot be global or static because, by definition, a virtual function is a

member function of a base class and relies on a specific object to determine which

implementation of the function is called. We can declare a virtual function to be a friend of another class.

If a function is declared virtual in its base class, we can still access it directly using the scope

resolution (::) operator. In this case, the virtual function call mechanism is suppressed and thefunction implementation defined in the base class is used. In addition, if we do not override a

virtual member function in a derived class, a call to that function uses the function

implementation defined in the base class.

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A virtual function must be one of the following:

· Defined

· Declared pure

· Defined and declared pure

A base class containing one or more pure virtual member functions is called an abstract class.

4. Describe the theoretical concepts of Binary files and Manipulators with relevantprogramming examples.

Ans:

Remaining answers are available in the full assignments (in MS-WORD format).

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