CBSE Guess > Papers > Important Questions > Class XII > 2008 > Computer Science > Computer Science By Mr. Shemeer. K. A.

CBSE CLASS XII

Q. 1. Distinguish between an object and a class.

Ans: An object is an identifiable entity with some characteristics and behaviour. A class is a group of objects that share common properties and relationships.

Q. 2. What is polymorphism? Give an example in C++ to show its implementation in C++.

Ans: Polymorphism is the property by which the same message can be processed in more than one form. This is of 2 types:

1. Function Overloading: Same function name can be used for more than one purpose.
2. Operator Overloading: Same operator can be used for more than one purpose.

Q. 3. How does a pointer variable differ from a simple variable?

Ans: A simple variable stores a data value whereas a pointer variable stores a memory address of another variable.

Q. 4. Name the header file to be included for the use of following built-in functions:

1. frexp( )
2. tooupper( )
3. getc( )
4. strcat( )
5. setw( )
   

Ans:

1. math.h
2. ctype.h
3. stdio.h
4. string.h
5. iomanip.h

Q. 5. Find the syntax errors:

# include(iostream.h)
void main( )
{
      int X, Y;
      cin>>X;
      for(Y=0;Y<10,Y++)
                  if X = = Y
                              cout<<Y+X;
                  else
                              cout<<Y:
}

Errors:

File iostream.h should be in angled brackets < > i.e. #include<iostream.h>

The condition and updation segments should be separated by a semicolon(;) i.e. For(Y=0;Y<10;Y++)

The condition should be enclosed in braces as shown below: i.e. if(X= = Y)

Statement should be terminated by ; i.e. cout<<Y;

Q. 6. Will the following program execute successfully? If not, state the reason(s):

# include<isotream.h>
void main( )
{
            int x, sum = 0;
            cin<<n;
            for(x=1,x<100,x+=2)
                        if x%2 = = 0
                                    sum += x;
                        cout>>”SUM=”>>SUM;
}

 

            Ans: #include<iostream.h>       
                    Wrong operator with cin. It should be cin>>n;
                    In place of if x%2 = = 0, it should be if(x%2 = = 0)
                    Wrong operator with cout. It should be cout<<”SUM=”<<SUM;

Q. 7. What will be the output:

int fun(int &x, int y=10)
{
            if(x%y = = 0) return ++x; else return y--;
}
void main( )
{
            int p=20, q=23;
            q = fun(p,q);
            cout<<p<<” “<<q<<endl;
            p = fun(q);
            cout<<p<<” “<<q<<endl;
            q = fun(p);
            cout<<p<<” “<<q<<endl;
}

Ans: Output is:
            20 23
            10 23
            11 11

Q. 8. Write a function in C++ to find the sum of the following series:

1+2+3+4+5+6+7+………. upto n terms.

Ans:

#include<iostream.h>
#include<conio.h>
int sum_series(int n);
void main( )
{
            clrscr( );
            int t = 0, sum = 0;
            cout<<”How many terms?”;
            cin>>t;
            sum = sum_series(t);
            cout<<”\n The sum of the series 1+2+3+4+....upto”<<t<<”is”<<sum;
}
int sum_series(int n)
{
            int s = 0;
            for(int i =1;i<=n;i++)
                        s+=i;
            return s;
}

Q. 9. Write a C++ function SUMFUN( ) having two parameters X of type double and n of type integer with a result type as double to find the sum of the series given below:

X + X2/3!+ X3/5!+…….+ Xn/(2n-1)!
            Ans:
                        double SUMFUN(double X, int N)
                        {
                                    int i,j;
                                    double sum = 0; fact;
                                    for(i=1;i<=n;++i)
                                    {
                                                fact = 1;
                                                for(j=1;j<=2*i-1;++j)
                                                            fact = fact * j;
                                                sum = sum + pow(x,i)/fact;
                                    }
                                    return sum;
                        }

Chapter 2 – Structures

Q. 10. Find the output of the following programs:

# include<iostream.h>

struct point
{
      int X,Y;
};
void show(point p)
{
      cout<<p.x<<’:’<<p.y<<endl;
}
void main( )
{
      point u = {20, 10}, v, w;
      v = u;
      v.x += 20;
      w = y;
      u.y += 10;
      u.x += 5;
      w.x -= 5;
      show(u);
                        show(v);
                        show(w);
                   }
Ans: Output is:
            25:20
            40:10
            35:10

Q .11. Rewrite the corrected code for the following program. Underline each correction.

#include<iostream.h>
structure club
{         
            int mem number;
            char memname[20];
            char memtype[] = “HELLO”;
};
void main( )
{
            club p1, p2;
            cin<<”Member Number:”;
            cin>>memnumber.p1;
            cout<<”Member Name:”;
            cin>>p1.membername;
            p1.memtype = “WORLD”;
            p2 = p1;
            cin<<”Member Number:”<<p2.memnumber;
            cin<<”Member Name:”<<p2.memname;
cin<<”Member Number;”<<p2.memtype;
}

Ans:

#include<iostream.h>
#include<string.h>
struct club
{         
            int memnumber;
            char memname[20];
            char memtype[6];
};
void main( )
{
            club p1, p2;
            cout<<”Member Number:”;
            cin>>p1.memnumber;
            cout<<”Member Name:”;
            cin>>p1.memname;
            strcpy(p1.memtype ,“WORLD”);
            p2 = p1;
            cout<<”Member Number:”<<p2.memnumber;
            cout<<”Member Name:”<<p2.memname;
cout<<”Member Type:”<<p2.memtype;
}

Chapter 3 – Object Oriented Programming

Q. 12. What do you understand by function overloading? Give an example illustrating its use in a C++ program.

Ans: A function name having several definitions that are differentiable by the number or types of their arguments is known as function overloading. For example;
            float area(float a)
            {
                        return a * a;
            }
            float area(float a, float b)
            {
                        return a * b;
            }

Q. 13. Enlist some advantages of OOP.

1. Reusability of code
2. Ease of comprehension
3. Ease of fabrication and maintenance
4. Easy redesign and extension.

Chapter 4 – Classes and Objects

Q. 14. Describe the methods of accessing data members and member functions of a class in the following cases:

1. Inside the main program
2. Inside a member function of the same class
3. Inside a member function of another class.           

Ans:

1. The public members can be accessed using the syntax
   Objectname.public membername;
2. All the members of the class are accessed as ordinary members. No class name or object name is required here.
3. Here only the public members are accessed using the objects of the same type i.e. Objectname.membername.

Q. 15. Define a class student with the following specifications:

Private members:
            rollno                integer
            name                character array of size 20
            class_st            character array of size 8
            marks               integer array of size 5
            percentage        float
            calculate           that calculates overall percentage marks and returns the percentage.

Public Members:
            readmarks reads marks and invokes the calculate function
            displaymarks prints the data.

Ans:

class student
{
            int roll_no;
            char name[20];
            char class_st[8];
            int marks[5];
            float percentage;
            float calculate;
public:
            void readmarks( );
            void displaydata( );
};
float student::calculate( )
{
            float p = 0;
            int tot = 0;
            for(int i =0; i<5; i++)
                        tot += marks[i];
            p = tot/5.0;
            return p;
}
void student::readmarks( )
{
            cout<<”Enter roll number”;
            cin>>roll_no;
            cout<<”Enter name:”;
            gets(name);
            cout<<”Enter class:”;
            gets(class_st);
            cout<<”Enter marks in 5 subjects:”;
            for(int i =0;i<5;i++)
                        cin>>marks[i];
}
void student::displaydata( )
{
            cout<<”Roll number:”<<roll_no<<endl;
            cout<<”Name:”<<name<<endl;
            cout<<”Class:”<<class_st<<endl;
            cout<<”Marks in 5 subjects:”;
            for(int i=0;i<5;i++)
                        cout<<marks[i]<<” “;
            cout<<endl;
            percentage = calculate( );
            cout<<”Percentage=”<<percentage<<”%”;
}

Q. 16. What are the advantages and disadvantages of inline functions?

Ans: The main advantage of inline functions is that they save on the overheads of a function call as the function is not invoked, rather its code is replaced in the program.

The major disadvantage of inline functions is that with more function calls, more memory is wasted as for every function call, the same function code is inserted in the program. Repeated occurrences of same function code waste memory space.

Chapter 5 – Constructors and Destructors

Q .17. Given the following C++ code, answer the questions i and ii:

class readbook
{
                                    public:
                                    readbook( )                  //Function1
                                    {
                                                cout<<”Open the Book”<<endl;
                                    }
                                    void readchapter( )       //Function 2
                                    {
                                                cout<<”Reading chapter one”<<endl;
                                    }
                                    ~readbook( )                //Function 3
                                    {
                                                cout<<”Close the book”<<endl;
                                    }
                        };

1. In OOP, what is Function 1 referred as and when does it get invoked/called?
2. In OOP, what is Function 3 referred as and when does it get invoked/called?

Ans:

1. Function 1 is referred to as constructor and it gets invoked when an object gets created.
   
2. Function 3 is referred to as Destructor and it gets invoked when an object goes out of scope.i.e. when its scope is over.

Q. 18. Define the following:

1. Default Constructor
2. Copy Constructor

Ans:

1. Default Constructor: A constructor that accepts no parameter is called default constructor.
2. Copy Constructor: A constructor that is invoked when an object is defined and initialized with another object. It takes the following form:

classname(classname &);

Q. 19. Distinguish between the following two statements:

time T1(13, 10, 25);                             //statement 1
time T1 = time(13,10,25);                     //statement 2

Ans: The first statement creates the object T1 by calling the time constructor implicitly. On the other hand, the second statement creates the object T1 by calling the time constructor explicitly.

Q. 20. Predict the output for the following code:

#include<iostream.h>
class student_rec
{
            int m1,m2,m3;
            float percentage;
public:
            student_rec( )
            {
                        m1 = m2 = m3 = 0;
                        percentage = 0.0;
            }
            void calc_perc(int x, int y, int z)
            {
                        m1 = x; m2 = y; m3 = z;
                        percentage = (m1+ m2 + m3)/3.0;
                        display_rec( );
            }
            void display_rec( )
            {
                        cout<<endl<<”Percentage=”<<percentage<<”%”;
            }
};
void main( )
{
            student_rec s1;
            s1.display_perc( );
            s1.calc_perc( );
            s1.display_perc( );
}

Ans: Percentage = 0%, Percentage = 35%

Chapter 6 – Inheritance

Q. 21. What is Containership? How does it differ from Inheritance?

Ans: When a class contains objects of another class as its members, this kind of relationship is called containership or nesting. Inheritance lets you create or define a specialized object of a class that shares the properties of the class and at the same time adds new features to it. But containership is just a way to define an object which itself is collection of objects of other classes.

Q .22. Given the following class definitions answer the questions that follow:

class book
{
            char title[20];
            char author[20];
            int no_of_pages;
public:
            void read( );
            void show( );
};
class textbook:private book
{
            int no_of_chapters, no_of_assignments;
protected:
            int standard;
public:
            void readtextbook( );
            void showtextbook( );
};
class physicsbook:public textbook
{
            char topic[20];
public:
            void readphysicsbook( );
            void showphysicsbook( );
};

1. Name the members, which can be accessed from the member functions of class physicsbook.
2. Name the members, which can be accessed by an object of class textbook.
3. Name the members, which can be accessed by an object of class physicsbook.
4. What will be the size of an object (in bytes) of class physicsbook.

Ans:

1. Data Members: standard, topic
   Member Functions: readtextbook( ), showtextbook( ), readphysicsbook( ); showphysicsbook( ).
2. Member Functions: readtextbook( ), showtextbook( ).
3. Member Functions: readtextbook( ), showtextbook( ), readphysicsbook( ), showphysicsbook( ).
4. 68 bytes.

Chapter 7 – Data File Handling

Q. 23. Write a user defined function in C++ to read the content from a text file STORY.TXT, count and display the number of alphabets present in it.

Ans:
            #include<fstream.h>
            void main( )
            {
                        ifstream fin(“STORY.TXT”);
                        char ch;
                        int count = 0;
                        if(!fin)
                        {
                                    cout<<”\n File does not exist”;
                                    return;
                        }
                        while(1)
                        {
                                    fin.get(ch);
                                    if(ch = = EOF)
                                                break;
                                    if((ch>=’A’ && ch<=’Z’)||(ch>=’a’&& ch<=’z’))
                                                count++;
                        }
                        cout<<”\nNumber of alphabets are:”<<count;
                        fin.close( );
            }

Q. 24. Name two member functions common to the classes ifstream and ofstream.

Ans: open ( ), close ( ).

Q. 25. Assuming the class Computer as follows:

class computer
{
            char chiptype[10];
            int speed;
public:
            void getdata( )
            {
                        gets(chiptype);
                        cin>>speed;
            }
            void showdata( )
            {
                        cout<<”Chip”<<chiptype<<”Speed=”<<speed;
            }
};

Write a function readfile( ) to read all the records present in an already existing binary file SHIP.DAT and display them on the screen, also count the number of records present in the file.

Ans:
            void readfile( )
            {
                        ifstream fin;
                        fin.open(“SHIP.DAT”,ios::in|ios::binary);
                        computer c;
                        while(!fin.eof( ))
                        {
                                    fin.read((char*)&c, sizeof(c));
                                    count++;
                                    c.showdata( );
                        }
                        cout<<”Total Number of Records are”<<count;
            }

Q. 26. Differentiate between write and put functions of ostream class.

Ans: The prototypes of put ( ) and write ( ) are:
            ostream & put (char ch);
            ostream & write ((char *) & buf, int sizeof(buf));

The put ( ) writes the value of ch(one character) to the stream and returns a reference to the stream. The write ( ) function writes sizeof (buf) bytes to the associated stream from the buffer pointed to by buf. The data written to a file using write( ) can only be read accurately using read( ).

Q. 27. Write a program that displays the size of a file in bytes:

Ans:
            #include<fstream.h>
            #include<process.h>
            #include<conio.h>
           
          void main( )
            {
                        clrscr( );
                        char filename[13];
                        cout<<”Enter filename:\n”;
                        cin.getline(filename, 13);
                        ifstream infile(filename);
                        if(!infile)
                        {
                                    cout<<”Cannot open “<<filename<<” file”;
                                    exit(-1);
                        }
                        int no_bytes = 0;
                        char ch;
                        while(cin.get(ch))
                                    no_bytes++;
                        cout<<”File size is”< no_bytes<<” bytes”;
                        getch( );
}

Chapter 8 – Pointers

Q. 28. Distinguish between:

int * ptr = new int(5);

int  *ptr = new int[5];

Ans:

The first statement allocates memory of one integer to ptr and initializes it with value 5. The second statement allocates memory of 5 contiguous integers (i.e. an array of 5 integers) and stores beginning address in pointer ptr.

Q. 29. What will be the output of the following code fragment:

#include<iostream.h>
#include<conio.h>
void main( )
{
            clrscr( );
            int a[ ] = {3, 5, 6, 7};
            int *p, **q, ***r, *s, *t, **ss;
            p = a;
            s = p + 1;
            q = &s;
            t = (*q + 1);
            ss = &t;
            r = &ss;
            cout<<*p<<’\t’<<**q<<’\t’<<***r<<endl;
}

Ans: 3, 5, 6.

Q. 30. Identify syntax errors, if any, in the following program. Also give reason for errors.

void main( )
{
            const int i = 20;
            const int * const ptr = &i;
            *ptr ++;
            int j = 15;
            ptr = &j;
}

Ans:

Chapter 9 –Array

Q. 31. How is computer memory allotted for a 2D array?

Ans: For two-dimensional array, the computer memory is allocated either in row-major form or in column-major form.

Row Major form stores the 2-D array row wise i.e., firstly the first row is stored, then the second row, then third row, and so forth.

Column Major form stores the 2-D array column wise i.e. firstly the first column, then the second column, then third and so forth. The default form is Row-Major.

Q. 32. Binary search is to be used on the following sorted array to search for 30 and 60.

Array

Give the index of the element that would be compared with at every step. Repeat the process replacing 30 by 60.

Ans:

For 30
Step                             Index                           Result
1.                                 4                                  Unsuccessful
2.                                 1                                  Unsuccessful
3.                                 2                                  Successful

For 60
Step                             Index                           Result
1.                                 4                                  Unsuccessful
2.                                 7                                  Successful.

Q. 33. Consider the single dimensional array AAA [45] having base address 300 and 4 bytes is the size of each element of the array. Find the address of AAA [10], AAA [25] and AAA [40].

Ans:

lb=0, b=300, s=4 bytes.
AAA [I] = b + (l – lb)*s
AAA [10] = 300 + (10-0)*4 = 340
AAA [25] = 300 + (25-0)*4 = 400
AAA [40] = 300 + (40-0)*4 = 460.

The addresses of AAA [10], AAA [25], AAA [40] are 340, 400 and 460 respectively.

Q .34. Given two dimensional array A[10][20], base address of A being 100 and width of each element is 4 bytes, find the location of A[8][15] when the array is stored as a) column wise b) Row wise.

Ans:

1. Column wise

            Address[i][j] = B + w[n(J-0)+(I-0)]
            Address A[8][15] = 100 + 4[10(15-0) + (8-0)] = 100 + 4[150 + 8] = 100 + 632 = 732.

2. Row wise

Address[i,j] =   B + w[n(I-0) + (J-0)]
Address A[8][15]=100 + 4[20(8 – 0) + (15 – 0)]= 100 + 4[160 + 15]= 100 + 700 = 800

Q. 35. Write a C++ function to find and display the sum of each row and each column of a 2 dimensional array of type float. Use the array and its size as parameters with float as the return type.

Ans:
            void rowcolsum(float a[10][10], int r, int c)
                        {
                                    int i,j;
                                    float rs[10], cs[10];
                                    for(i=0;i<r;i++)
                                    {
                                                rs[i] = 0;
                                                for(j=0;j<c;j++)
                                                            rs[i] = rs[i] + a[i][j];
                                    }

for(j=0;j<c;j++)
                                    {
                                                cs[j] = 0;
                                                for(i=0;i<r;i++)
                                                            cs[j] = cs[j] + a[i][j];
                                    }
                        //Display 2 D array with row sum and column sum
                                    for(i=0;i<r;i++)
                                    {
                                                for(j=0;j<c;j++)
                                                            cout<<a[i][j]<<” “;
                                                cout<<rs[i]<<endl;
                                    }
                        for(j=0;j<c;j++)
                                    cout<<cs[j]<<” “;
                        cout<<endl;
}

Chapter 10 – Linked Lists, Stacks and Queues

Q. 36. Differentiate between a FIFO list and LIFO list.

Ans: A FIFO (First In First Out) list processes its elements in first come first served basis.
A LIFO (Last In First Out) list is processed in LIFO manner i.e., elements that entered last are removed first of all.

Q. 37. Transform the following expression to prefix and postfix form:

(A + B * C – D)/E * F

Ans:

i) Postfix form  
(A + B * C – D)/E * F = ((A + (B * C)) – D)/ (E * F)
                                    = ((A + (BC*)) – D)/ (EF *)
                                    = ((ABC * +) – D)/ (EF *)
                                    = ((ABC * + D –))/EF*
                                    = ABC * + D – EF */
            ii) Prefix form
                        (A + B * C – D)/E * F = ((A + (B * C)) – D)/ (E * F)
                                                            = ((A + (*BC)) – D)/(*EF)
                                                            = ((+A * BC) – D)/(*EF)
                                                            = (- + A * BCD)/(*EF)
                                                            = / - + A * BCD * EF

Q. 38. Transform the following expressions to infix form:

1. + - ABC
2. + A – BC

Ans:

1. +(A – B)C = (A – B) + C
2. + A(B – C) = A + (B – C)

Q. 39. Evaluate the following postfix expression using a stack and show the contents of the stack after execution of each operation

5, 6, 9, +, 80, 5, *, -, /

Ans: Scan from left to right

The result is: -1/77

Q. 40. Give the necessary declaration of a linked implemented stack containing integer type numbers; also write a user defined function in C++ to pop a number from this stack.

Ans:
            struct stack
            {
                        int info;
                        stack *next;
            }*top, *ptr;
            void pop( )
            {
                        if(!top)
                        {
                                    cout<<”underflow \n”;
                                    exit(1);
                        }
                        else
                        {
                                    cout<<top->info;
                                    ptr = top;
                                    top = top -> next;
                                    ptr -> next = null;
                                    delete ptr;
                        }
            }

Chapter 11 – Database Concepts

Q. 41. What is a relation? What is the difference between a tuple and an attribute?

Ans: A relation is a table having atomic values, unique rows and unordered rows and columns. A row in a relation is known as tuple whereas a column of a table is known as an attribute.

Q. 42. Define the following terms:

1. Degree
2. Cardinality

Ans:

1. Degree: The number of attributes (columns) in a relation determine the degree of a relation.
2. Cardinality: The number of tuples (rows) in a relation is called the cardinality of the relation.

Chapter 12 – Structured Query Language

Q. 43. What are DDL and DML?

Ans: The DDL provides statements for the creation and deletion of tables and indexes.
The DML provides statements to enter, update, delete data and perform complex queries on these tables.

Q. 44. Given the following tables for a database LIBRARY:

Table: Books

Table: Issued

Write SQL queries for (a) to (f):

1. To show Book name, Author Name, and Price of books of EPB publishers.
2. To list the names of books of fiction type.
3. To display the names and price of the books in descending order of their price.
4. To increase the price of al books of first publ by 50.
5. To display the Book_Id, Book_Name, and Quantity_Issued for all books which have been issued.
6. To insert a new row in the table Issued having the following data: “F002”, 4.
7. Give the output of the following queries based on the above tables:

1. SELECT COUNT (DISTINCT Publishers) FROM Books.
2. SELECT SUM (Price) FROM Books WHERE Quantity>5
3. SELECT Book_Name, Author_Name FROM Books WHERE Price<500
4. SELECT COUNT (*) FROM Books.

Ans:

1. SELECT Book_Name, Author_Name, Price
   FROM Books WHERE Publishers = “EPB”;
2. SELECT Book_Name FROM Books WHERE Type = “Fiction”;
3. SELECT Book_Name, Price FROM Books ORDER BY Price DESC;
4. UPDATE Book SET Price = Price + 50 WHERE Publishers = “First Publ”;
5. SELECT Books.Book_Id, Book_Name, Quantity_Issued FROM Books, Issued WHERE Books.Book_Id = Issued.Book_Id;
6. INSERT INTO issued VALUES(“F002”, 4);
7. i) 3
   ii) 1350
   iii) My First C++                Brian & Brooke
         C++ Brainworks          A.W.Rossaine
         Fast Cook                    Lata Kapoor
   iv) 5

Chapter 13 – Boolean Algebra

Q. 45. State the principle of duality in Boolean Algebra and give the dual of the Boolean expression (X + Y) . (X’ + Z’) . (Y + Z)

Ans: Principle of Duality states that from every Boolean relation, another boolean relation can be derived by

1. Changing each OR sign to AND and vice versa
2. Replacing each 1 by 0 and vice versa.

The new derived relation is known as the dual of the original relation.
Dual of  (X + Y) . (X’ + Z’) . (Y + Z) is X.Y + X’.Z’ + Y.Z

Q. 46. Seven inverters are cascaded one after another. What is the output if the input is 1?

Ans: 0.

Q. 47. Why are NAND and NOR gates called Universal Gates?

Ans: NAND and NOR gates are less expensive and easier to design. Also other functions (NOT, AND, OR) can easily be implemented using NAND/NOR gates.

Q. 48. Obtain a simplified form for the following Boolean Expression using Karnaugh’s Map:

F(a, b, c, d) = ∑(0, 1, 2, 4, 5, 7, 8, 9, 10, 11, 14).

Ans:

            Quad 1 = a’c’  , Quad 2 = ab’ , Pair 1 is a’bd,   Pair 2 is b’cd’ , Pair 3 is acd’

            The simplified form is: a’c’ + ab’ + a’bd + b’cd’ + acd’

Q. 49. State and prove Associative Law with the help of Truth Table.

Chapter 14 – Communication and Network Concepts

Q .50. What is meant by Network Topology?

Ans: The pattern of interconnection of nodes in a network is called the network topology. Major topologies are:

1. Star
2. Bus
3. Ring or Circular
4. Tree
5. Graph

Q. 51. What are Bridges? How do they differ from Repeaters?

Ans: Bridge is a device that links two networks together. Bridges differ from repeaters in their capability of deciding whether a particular message is to be communicated on the other side or not where as a repeater just amplifies the signal and pass it to other side.

Q. 52. Give the full form for the following:

1. MODEM
2. FM
3. AM
4. NFS
5. FTP

Ans:

1.  Modulator Demodulator 
2. Frequency Modulation
3. Amplitude Modulation
4. Network File Server
5. File Transfer Protocol.