CSS Computer Science Paper 2018

FEDERAL PUBLIC SERVICE COMMISSION
COMPETITIVE EXAMINATION FOR RECRUITMENT TO POSTS
IN BPS-17 UNDER THE FEDERAL GOVERNMENT, 2018

COMPUTER SCIENCE, PAPER-I

PART-II
SECTION-I

Q. 2. (a) How many layers are in the TCP/IP stack? What are the names?

(b) How digital evidences can be preserved from a crime scene. Write in details by taking
examples of digital devices commonly used these days.
(c) What are the responsibilities of Operating system kernel?
(d) List down any four best practices for coding standards.
(e) Why do modern processors use more power when their clock frequency is increased?
(f) Ali is telling Ahmad that he is representing a -ve number and its most significant bit is 1,
Ahmad immediately shouted you are representing numbers using 2's compliment. True
or False. And why?
(g) If time slice is of 50 milliseconds and context switch requires a microsecond, how many
processes can the machine service in a second?
(4)
(4)
(3)
(3)
(2)
(2)
(2)
Q. 3. (a) Write a program grade average calculator, User will input marks for five subjects and
program will output the average of its marks. Print appropriate message on the base of
its mark's average e.g.; Well done, Keep it up, Better luck next time etc.
(b) Given that i,j,k,n & m are integer variables. Write a condition such that:
i- hello is only printed when, any of the following conditions are met: i is twice
the value of j, j is smaller than k and less than n, or m is negative.
inti,j,k,n,m; cin>>i>>j>>k>>n>>m;
if( )
cout<<”hello”;
ii. hello is only printed when i does not lies in the interval 6-9
inti; cin>>i;
if( )
cout<<“hello”;
(c) Write equivalent instruction to following instruction without the use of += operator:
where w,z are integers.
w+=2*z+4;
(d) Predict the values of variables a & b after every instruction
integer a=5 b=6
a=(b++) + 3;
b=--a;
(e) Complete the code such that it prompts the user for +ve number n. Then displays the
output.(whatever the value of n is)(HINT: instead of triangles of stars its triangles of
increasing numbers)[marks
1 2 3 4 . . . n
1 2 3 4 ..n-1
. . .
. . .
1 2
1

for n=4 it will print
1 2 3 4
1 2 3
1 2
1
void main()
{
int n; cin>>n;
// your loops will go here
}
(f) In following code replace the character at posth location in the string st with the ,character
ch. For example in string helloworld replacing 2nd character with i would result in
hilloworld
void main( )
{char st[15]; int pos; char ch;
int size=0;
cin>>st;
cin>>pos>>ch;
while(st[size]!='\0')
{
size++; // calculating length of current string
}
// write your code here
}
(5)

Q. 4. Consider the inheritance hierarchy shown below. Each part of this question is independent.
(a) In which class(es) would it make most sense to have protected members? Which class(es)
would be able to access those protected members directly?
(b) Which class(es) can access private members of class C directly?
(c) Suppose class C contains a pure virtual function. Suppose we wish to instantiate objects of
this hierarchy. Which class(es) are or could be abstract and which are concrete?
(d) Consider the following list of classes: Car, SteeringWheel, Vehicle, Van, Minivan,
AudioSystem, ParkingLot. Your task is to describe all of the is-a and has-a relationships
between these classes. Include an inheritance hierarchy for all classes that fit. Fill in the
table with is-a or has-a relationship while leaving the cells empty where no relation is
applicable.
Vehicle Car Van Mini
Van
Steering
Wheel
Audio
System
Parking
Lot
Vehicle
Car is-a
Van
Mini Van
Steering Wheel
Audio System
Parking Lot

Q. 5. (a) What is dangling pointer?

(b) What data structure would employ to build a text editor and why?
(c) Random insertion of nodes into a binary search tree would result in what types of tree
shape. Elaborate.
(d) How would you modify a link list based queue so that first and last node can be accessed
in a constant time regardless of data nodes in the queue?
(3)
(5)
(7)
(5)

Q. 6. (a) Define balanced tree both for AVL and Binary search tree.

(b) What is informed or heuristic search what type of algorithm is used to do such a search?
(c) Differentiate between graph and trees. Which is special case of the other?
(d) Explain what type of problems can be solved by genetic algorithm.
(4)
(6)
(5)
(5)

Q. 7. (a) Outline the difference between software verification and software validation.

(b) Give an outline of the unit testing process for verification.
(c) Agile Development is a process that values responding to change over following a plan.
Discuss three issues a Software Engineer should be mindful of when adopting this
approach during software development.
(d) What type of project is not suited to incremental methods?
(e) Outline the difference between Black box and White box testing.
(4)
(4)
(4)
(4)
(4)

Q. 8. (a) What is the difference between lexers and parsers?

(b) Write a grammar (BNF) for the language of palindromes.
(c) Here DFA is given for the language L find the DFA for L2

(d) Convert the following DFA to a RE:

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