## Year 2011

0

**ISC 2011**

**COMPUTER SCIENCE PAPER 1**

**THEORY**

**Question 1.**

a) State the two absorption laws. Verify any one of them using truth table.

b) Reduce the following expression :

F(A,B,C)= Σ(0,1,2,3,4,5,6,7)

Also find the complement of the reduced expression.

c) Name the logic gate for the following circuit diagram and write its truth table.

d) Using truth table, verify whether the following is true or false:

(p →q) = (q’→p’)

e) If A=1, B=0, C=1 and D=1 find its

i) maxterm

ii) minterm

[2 x 5 =10]

**Question 2.**

a) How can we override a method in inheritance?

b) A square matrix A[m x m] is stored in the memory with each element requiring 2 bytes of

storage. If the base address A[1][1] is 1098 and the address at A[4][5] is 1144, determine the

order of the matrix A[mxm] when the matrix is stored column majorwise.

c) What is Big O Notation?

d) What is an exception?

e) Convert the infix expression to its postfix form:

A+B*C-D/E

[ 2 x 5 =10]

**Question 3.**

a) The following is a part of some class. What will be the output of the function mymethod( )

when the value of counter is equal to 3? Show the dry run/ working.

void mymethod(int counter)

{

if(counter= =0)

System.out.println(“ “);

else

{

System.out.println(“Hello “+ counter);

mymethod(- -counter);

System.out.println(“ “+ counter);

}

} [ 5]

b) The following function is a part of some class which computes and returns the greatest

common divisor of any two numbers. There are some places in the code marked by ?1?, ?2?,

?3?, ?4?, and ?5? which must be replaced by statement/expression so that the function works

correctly.

int gcd(int a, int b)

{

int r;

while(?1?)

{

r=?2?;

b=?3?;

a=?4?;

}

if(a==0)

return ?5?;

else

return -1;

}

i) What is the expression or statement at ?1?

ii) What is the expression or statement at ?2?

iii) What is the expression or statement at ?3?

iv) What is the expression or statement at ?4?

v) What is the expression or statement at ?5?

[ 1 x 5 = 5]

**Part II**

**Answer seven questions in this Part, choosing three questions from Section A and two questions from**

**Section B and two questions from Section C.**

**Section A**

**Answer any three questions from this Section**

**Question 4.**

a) State the principle of duality. Give the dual of the following:

(A’B)+(C.1)=(A’+C)(B+C) [ 3 ]

b) Reduce the following Boolean expressions to their simplest forms:-

i) {(CD)’+A} + A+ C.D + A.B

ii) A.{B+C(A.B + A.C)’} [ 4]

c) Verify using a truth table if:

(A B C)’ = A B C [ 3 ]

**Question 5.**

a) Given F(P,Q,R,S)= π(2,3,6,7,9,11,12,13,14,15)

Reduce the above expression using four variable K-map. Draw the logic gate diagram of the

reduced expression using NOR gates only. [ 5]

b) Given F(A,B,C,D)= A’B’C’D’ + A’B’C’D + AB’C’D’+ AB’C’D + A’BC’D’ +A’BCD’.

Reduce the above expression by using four variable K-map. Draw the logic gate diagram of the

reduced expression using NAND gates only. [ 5]

**Question 6.**

a) Show with the help of a logic diagram how a NAND gate is equivalent to an OR gate. [ 3 ]

b) Verify if the following is valid:

(A→B) ^ (A→C)= A→(B^C) [ 3 ]

c) What is a decoder? Draw the truth table and logic circuit diagram for a 2 to 4 decoder. [ 4 ]

**Question 7.**

a) What is a Full Adder? Draw the truth table for a Full Adder. Also derive SOP expression for the

Full Adder and draw its logic circuit. [ 4 ]

b) State how a decoder is different from a multiplexer. Also state one use of each. [ 3 ]

c) Convert the following cardinal expression into its canonical form and reduce it using Boolean

laws: F(L,M,O,P) = π(0,2,8,10) [ 3 ]

**Section B**

**Answer any 2 questions.**

**Each program should be written in such a way that it clearly depicts the logic of the problem. This can be**

**achieved by using mnemonic names and comments in the program.**

**Question 8.**

Input a sentence from the user and count the number of times, the words “an” and “and” are present in

the sentence. Design a class Frequency using the description given below:

Class name : Frequency

Data Members

text : stores the sentence

countand : to store the frequency of the word and.

countan : to store the frequency of the word an.

len : stores the length of the string.

Member functions

Frequency() : constructor to initialize the data variables.

void accept(String n) : to assign n to text where the value of the parameter should be

in lowercase.

void checkandfreq() : to count the frequency of and.

void checkanfreq() : to count the frequency of an.

void display() : to display the frequency of “an” and “and” with suitable

messages.

Specify class Frequency giving details of the constructor(), void accept(String), void checkand freq() and

void display(). Also define the main function to create an object and call methods accordingly to enable

the task. [ 10 ]

**Question 9.**

A class DeciOct has been defined to convert a decimal number into its equivalent octal number. Some of

the members of the class are given below:

Class name : DeciOct

Data members

n : stores the decimal number

oct : stores the equivalent octal number

Member functions:

DeciOct() : constructor to initialize the data members to 0

void getnum(int nn) : assigns nn to n

void deci_oct() : calculates the octal equivalent of n and stores it in oct using the

recursive technique

void show() : displays the decimal number n calls the function deci_oct() and

displays its octal equivalent

a) Specify the class DeciOct, giving details of the constructor(), void getnum(int), void deci_oct()

and void show(). Also define a main function to create an object and call the functions

accordingly to enable the task. [ 8 ]

b) State any two disadvantages of using recursion. [ 2 ]

**Question 10.**

You are given a sequence of n integers, which are called pseudo arithmetic sequences ( sequences that

are in arithmetic progression).

Sequence of n integers : 2, 5, 6, 8, 9, 12

We observe that 2 + 12 = 5 + 9 = 6 +8 = 14

The sum of the above sequence can be calculated as 14 x 3 = 42

For sequence containing an odd number of elements the rule is to double the middle element, for

example 2, 5, 7, 9, 12

=2 +12 = 5 +9 = 7 +7 = 14

14 x 3 = 42 [ middle element = 7]

A class pseudoarithmetic determines whether a given sequence is pseudo-arithmetic sequence. The

details of the class are given below:-

Class name : Pseudoarithmetic

Data members

n : to store the size of the sequence

a[ ] : integer array to store the sequence of numbers

ans, flag : to store the status

sum : to store the sum of sequence of numbers

r : to store the sum of 2 numbers

Member functions :

Pseudoarithmetic( ) : default constructor

void accept(int nn ) : to assign nn to n and to create an integer array. Fill in the

elements of the array.

boolean check( ) : return true if the sequence is a pseudo-arithmetic sequence

otherwise return false.

Specify the class Pseudoarithmetic, giving details of the constructor(), void accept(int) and Boolean

check(). Also define the main function to create an object and call methods accordingly to enable the

task. [ 10]

**Section C**

**Answer any 2 questions.**

**Each program/algorithm should be written in such a way that it clearly depicts the logic of the problem**

**step wise. This can also be achieved by using pseudo codes.**

**(Flowcharts are not required)**

**The programs must be written in Java.**

**The algorithm must be written in general standard form wherever required.**

**Question 11.**

A super class Record has been defined to store the names and ranks of 50 students. Define a sub class

Rank to find the highest rank along with the name. The details of both classes are given below:

Class name : Record

Data members

name[] : to store the names of students

rnk[] : to store the ranks of students

Member functions:

Record() : constructor to initialize data members

void readvalues() : to store names and ranks

void display() : displays the names and the corresponding ranks

class name : Rank

Data members

index : integer to store the index of the topmost rank

Member functions

Rank() : constructor to invoke the base class constructor and to

initialize index to 0.

void highest() : finds the index location of the topmost rank and stores

it in index without sorting the array

void display() : displays the name and ranks along with the name

having the topmost rank.

Specify the class Record giving details of the constructor(), void readvalues(), void display(). Using the

concept of inheritance, specify the class Rank giving details of constructor(), void highest() and void

display(). The main function and algorithm need not be written.

**Question 12.**

Stack is a kind of data structure which can store elements with the restriction that an element can be

added or removed from the top only. The details of class Stack are given below:

Class name : Stack

st[] : the array to hold names.

size : the maximum capacity of the string array

top : the index of the topmost element of the stack

ctr : to count the number of elements of the stack

Member functions

Stack() : default constructor

Stack(int cap) : constructor to initialize size=cap and top=-1

void pushname(String n) : to push a name into the stack. If the stack is full, display

the message “overflow”.

String popname() : removes a name from the top of the stack and returns

it. If the stack is empty, display the message

“underflow”.

void display() : Display the elements of the stack.

a) Specify class Stack giving details of the constructors(), void pushname(String n), String

popname() and void display(). The main function and algorithm need not be written.

b) Under what principle does the above entity work?

**Question 13.**

a) A linked list is formed from the objects of the class,

class Node

{

int info;

Node link;

}

Write an algorithm OR a method for deleting a node from a linked list. The method declaration

is given below:

void deletenode(Node start)

b) Distinguish between worst-case and best-case complexity of an algorithm.

c) Answer the following from the diagram of a Binary tree given below:

7

i) Write the postorder tree traversal

ii) Name the leaves of the tree

iii) Height of the tree

iv) Root of the tree

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