Thursday, July 16, 2015

Technical Operating Systems


Technical Operating Systems


1.Explain the concept of Reentrancy.
It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.
Note: A reentrant procedure can be interrupted and called by an interrupting program, and still execute correctly on returning to the procedure.

2.Explain Belady's Anomaly.
Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process' virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.

3.What is a binary semaphore? What is its use?
A binary semaphore is one, which takes only 0 and 1 as values. They are used to implement mutual exclusion and synchronize concurrent processes.

4.What is thrashing?
It is a phenomenon in virtual memory schemes when the processor spends most of its time swapping pages, rather than executing instructions. This is due to an inordinate number of page faults.

5.List the Coffman's conditions that lead to a deadlock.
Mutual Exclusion: Only one process may use a critical resource at a time.
Hold & Wait: A process may be allocated some resources while waiting for others.
No Pre-emption: No resource can be forcible removed from a process holding it.
Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain.


6.What are short-, long- and medium-term scheduling?
Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.
Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.
Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.

7.What are turnaround time and response time?
Turnaround time is the interval between the submission of a job and its completion. Response time is the interval between submission of a request, and the first response to that request.

8.What are the typical elements of a process image?
User data: Modifiable part of user space. May include program data, user stack area, and programs that may be modified.
User program: The instructions to be executed.
System Stack: Each process has one or more LIFO stacks associated with it. Used to store parameters and calling addresses for procedure and system calls.
Process control Block (PCB): Info needed by the OS to control processes.

9.What is the Translation Lookaside Buffer (TLB)?
In a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup. TLB contains those page-table entries that have been most recently used. Normally, each virtual memory reference causes 2 physical memory accesses-- one to fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit.

10.What is the resident set and working set of a process?
Resident set is that portion of the process image that is actually in real-memory at a particular instant. Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques.)
Technical Operating Systems

11.When is a system in safe state?

The set of dispatchable processes is in a safe state if there exists at least one temporal order in which all processes can be run to completion without resulting in a deadlock.

12.What is cycle stealing?
We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at specific break points in an instruction cycle.

13.What is meant by arm-stickiness?
If one or a few processes have a high access rate to data on one track of a storage disk, then they may monopolize the device by repeated requests to that track. This generally happens with most common device scheduling algorithms (LIFO, SSTF, C-SCAN, etc). High-density multisurface disks are more likely to be affected by this than low density ones.

14.What are the stipulations of C2 level security?
C2 level security provides for:
Discretionary Access Control
Identification and Authentication
Auditing
Resource reuse

15.What is busy waiting?
The repeated execution of a loop of code while waiting for an event to occur is called busy-waiting. The CPU is not engaged in any real productive activity during this period, and the process does not progress toward completion.

16.Explain the popular multiprocessor thread-scheduling strategies.
Load Sharing: Processes are not assigned to a particular processor. A global queue of threads is maintained. Each processor, when idle, selects a thread from this queue. Note that load balancing refers to a scheme where work is allocated to processors on a more permanent basis.
Gang Scheduling: A set of related threads is scheduled to run on a set of processors at the same time, on a 1-to-1 basis. Closely related threads / processes may be scheduled this way to reduce synchronization blocking, and minimize process switching. Group scheduling predated this strategy.
Dedicated processor assignment: Provides implicit scheduling defined by assignment of threads to processors. For the duration of program execution, each program is allocated a set of processors equal in number to the number of threads in the program. Processors are chosen from the available pool.
Dynamic scheduling: The number of thread in a program can be altered during the course of execution.

17.When does the condition 'rendezvous' arise?
In message passing, it is the condition in which, both, the sender and receiver are blocked until the message is delivered.

18.What is a trap and trapdoor?
Trapdoor is a secret undocumented entry point into a program used to grant access without normal methods of access authentication. A trap is a software interrupt, usually the result of an error condition.

19.What are local and global page replacements?
Local replacement means that an incoming page is brought in only to the relevant process' address space. Global replacement policy allows any page frame from any process to be replaced. The latter is applicable to variable partitions model only.

20.Define latency, transfer and seek time with respect to disk I/O.
Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time.
Technical Operating Systems

21.Describe the Buddy system of memory allocation.
Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.

22.What is time-stamping?
It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti
23.How are the wait/signal operations for monitor different from those for semaphores?
If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So this allows easier program design. Whereas in semaphores, every operation affects the value of the semaphore, so the wait and signal operations should be perfectly balanced in the program.


24.In the context of memory management, what are placement and replacement algorithms?
Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.

25.In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?
For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.
With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.

26.What are demand- and pre-paging?
With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.

27.Paging a memory management function, while multiprogramming a processor management function, are the two interdependent?
Yes.

28.What is page cannibalizing?
Page swapping or page replacements are called page cannibalizing.

29.What has triggered the need for multitasking in PCs?
Increased speed and memory capacity of microprocessors together with the support fir virtual memory and
Growth of client server computing

30.What are the four layers that Windows NT have in order to achieve independence?
Hardware abstraction layer
Kernel
Subsystems
System Services. 

Technical Operating Systems

31.What is SMP?
To achieve maximum efficiency and reliability a mode of operation known as symmetric multiprocessing is used. In essence, with SMP any process or threads can be assigned to any processor.

32.What are the key object oriented concepts used by Windows NT?
Encapsulation
Object class and instance

33.Is Windows NT a full blown object oriented operating system? Give reasons.
No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within one executive component and are not represented as objects and it does not support object oriented capabilities .

34.What is a drawback of MVT?
It does not have the features like
ability to support multiple processors
virtual storage
source level debugging

35.What is process spawning?
When the OS at the explicit request of another process creates a process, this action is called process spawning.

How many jobs can be run concurrently on MVT?
15 jobs

List out some reasons for process termination.
Normal completion
Time limit exceeded
Memory unavailable
Bounds violation
Protection error
Arithmetic error
Time overrun
I/O failure
Invalid instruction
Privileged instruction
Data misuse
Operator or OS intervention
Parent termination.

What are the reasons for process suspension?
swapping
interactive user request
timing
parent process request

What is process migration?

It is the transfer of sufficient amount of the state of process from one machine to the target machine

What is mutant?
In Windows NT a mutant provides kernel mode or user mode mutual exclusion with the notion of ownership.

What is an idle thread?
The special thread a dispatcher will execute when no ready thread is found.

What is FtDisk?
It is a fault tolerance disk driver for Windows NT.

What are the possible threads a thread can have?
Ready
Standby
Running
Waiting
Transition
Terminated.

What are rings in Windows NT?
Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode.

What is Executive in Windows NT?
In Windows NT, executive refers to the operating system code that runs in kernel mode.

What are the sub-components of I/O manager in Windows NT?
Network redirector/ Server
Cache manager.
File systems
Network driver
Device driver

What are DDks? Name an operating system that includes this feature.
DDks are device driver kits, which are equivalent to SDKs for writing device drivers. Windows NT includes DDks.

What level of security does Windows NT meets?
C2 level security.
Technical Operating Systems

Physics questions and answers

Physics questions and answers
Q1. Two bodies changed from p1v1 to p2v2 state in two ways. The heat supplied is delta Q and work done is delta W
Then what is constant in these two processes

(a) delta q
(b) delta w
(c) delta q + delta w
(d) delta q - delta w

Ans. (d)


Q2. _______ have same atomic number and same mass number are

(a) Isotopes
(b) Isotones
(c) Isomers
(d) Isobars

Ans. (c)


Q3. When a free electron is placed in a plane of electro magnetic then it moves in

(a) in the direction of the electric field
(b) in the direction of magnetic field
(c) of propagation of wave
(d) of the plane containing magnetic field and propagation direction.


Q4. Name the phenomena in which one proton is jumped from one isomer to another isomer to create two different elements

(a) functional isomerisim
(b) sterio merisim
(c) tauto merisim
(d) penta merisim

Ans. (c)


Q5. In the below compounds which one has 40% C ,6.7% H and 53.3 % O what is its empherical formula

(a) CHO
(b) CH2
(c) C2H2O2
(d) C2H3O2

Ans: (b)


Q6. X rays are coming from X ray tube, the wavelength is _______ a certain wavelength/s

(a) below
(b) above
(c) inbetween
(d) out of

Ans. (c)


Q7. In a triode valve in order to increase the saturation current what has to be done

(a) increase plate voltage
(b) reduce distance between grid and plate
(c) increase cathode potential
(d) reduce grid potential

Ans. (d )


Q8. Seven different toys are distributed among 3 children how many different ways are possible?

(a) 7C3
(b) 7P3
(c) 3 7
(d) 7 3

Ans. (c)


Q9. A, B ans C are three speakers. They have to speak randomly along with another 5 speakers in a function.
A has to speak before B and B has to speak before C. What is the probability.

Ans. 1/6


Q10. If dy = (secx + ytanx)dx, Then the curve is

(a) x = ycosx
(b) x = ysinx
(c) x = ytanx
(d) x = ysecx

Ans. (a)


Q11. Two series are 16,21,26.... and 17,21,25.....
What is the sum of first hundred common numbers

(a) 101100
(b) 110100
(c) 101110
(d) 110101

Ans. (a)


Q12. There are two sections in a question paper each contain five questions. A students has to answer 6 questions.
Maximum no. of questions that can be answered from any section is 4. How many ways he can attempt the paper?

(a) 50
(b) 100
(c) 120
(d) 200

Ans. (d)


Q13. a and b are two numbers selected randomly from 1,2,3.... 25 what is the probability of a and b are not equal.

(a) 1/25
(b) 24/25
(c) 13/25
(d) 2/25

Ans. (b)


Q14. The sum of the series 1 + 1(1+1/n) + 3(1+1/n)2 + ..... is equal to?

Ans. n2


Q15. Two circles of different radii intersects each other what is the maximum no of intersections

(a) 0
(b) 1
(c) 2
(d) 3

Ans. (c)


Q16. If x= sin-1(t), y = log(1-t2), find d2y/dx2 when t=1/2

(a) 1
(b) 0
(c) -8/3
(d) -2/3

Ans. (c)


Q17. If x approaches infinity , then (òex dx )/( òe2xdx) is ?

(a) 1
(b) 0
(c) -1
(d) 2

Ans. (a)


Q18. If f(x)=1-cos(1-cosx)/x4 is continuos at f(0) then what is x

(a) 1
(b) 0
(c) 1/4
(d) -1/4

Ans. (c)


Q19. For the word SURITI, if you arrange the letters in dictionary order then what is its rank?

(a) 234
(b) 235
(c) 236
(d) 237

Ans. (c)


Q20. Period of sin ((2t + 3) / 6 pi)

(a) 6pi
(b) 6pi2
(c) 3pi

Ans. (b)


Q21 - Q23. Four questions given on the below data


X,Yand Z are senior engineers. A,B,C,D are junior engineers. Company wants to select 4 enginers. Two will be senior and two will be juniors. The company wants these engineers to work in the most productive way so they respect each person's likes/dislikes.

Y is not friends with A

Z is not friends with C

B is not friends with A

If B is selected then who will be the remaining 4 members ?

If C is selected, Z and ___ cannot be selected?

D is always selected if ___ is selected?


Q24. A speaks truth 70% of the times, B speaks truth 80% of the times.
What is the probability that both are contradicting each other is ?


Q25. ò((2x-3)/((x2 +x+1)2 )dx is ?


Q26. Ram starts from A walking 2 km North and turns right and walks 4 km and turns right again and walks 4 km and turns right again and walks 4 km and meets Radha at Bwalking in the opposite direction to Ram .
a) Which direction does Ram walk after the first turn?
b) Distance between A and B


Q27. If the equation x2 - 3x + a = 0 has the roots (0,1) then value of a is ?


Q28. A and B's temperature are 10°c and 20°c having same surface , then their ratio of rate of emmisions is ?


Q29. An atomic particle exists and has a particlular decay rate . It is in a train . When the train moves, a person observes for whether the decay rate

(a) increases
(b) decreases
(c) depend on the directions of movement of train


Q30. Which of the following exchanges positive ions

(a).cl-
(b) nh2-
(c) ch2

Ans. (b)


Q31. After execution of CMP, a instruction in Intel 8085 microprocessor

(a) ZF is set and CY is reset.
(b) ZF is set CY is unchanged
(c) ZF is reset, CY is set
(d) ZF is reset , CY is unchanged .

Ans. ZF is set and CY is reset


Q32. The best tool for editing a graphic image is ?


Q33. Network scheme defines
a.)one to one
b.) many to many
c.) one to ,many ?


Q34. A person wants to measures the length of a rod.First he measures with standing ideally then he maeasures by
moving parrel to the rod

(a)the length will decrease in second case
(b)length will be same
(c) length will increse in the second case.


Q35. One U-230 nucleus is placed in a train moving by velocity emiting alpha rays .When the train is at rest the
distance between nucleus and alpha particle is x . One passenger is observing the particle . When the train is moving
what is the distance between particle and nucleus ?

(a) x
(b) x + vt
(c) x - vt

Q36. What is the resulting solution when benzene and toluene are mixed ?


Q37. If the word FADENCOMT equals 345687921 then

What is FEAT

Find representation of 2998


Q38. Given 10 alphabets out of which 5 are to be chosen. How many words can be made with atleast one repetition.


Q39. Arrange by acidic values : phenol, nitrotolouene and o-cresol?


Q40. Find sum of 3 + 5/(1+22) + 7/(1 + 22 + 32) + ......

Ans. 3n/(1 + n)


The following are few sample questions that maybe asked in the software paper.We haven't been able to give the values in certain problems ; only the type of questions have been mentioned.

Q What sorting algos have their best and worst case times equal ?
Ans. O(nlogn) for mergesort and heap sort

Q. What page replacement algo . has minimumn number of page faults ?
Ans. Optimality algorithm

Q. What is the use of virtual base class in c++
Ans. Multiple lines between derived classes.

Q. Find the eccentricity of a given node in a directed graph

Q. Convert the infix to postfix for A-(B+C)*(D/E)
Ans. ABC+DE/*-

Q. What is swapping

Q. Assignment operator targets to
Ans. l-value

Q. A byte addressable computer has memory capacity of 2 power m Kbytes and can perform 2 power n operations
an instruction involving three operands and one operator needs maximum of ---bits
Ans. 3m + n

Q. In round robin scheduling, if time quatum is too large then it degenerates to
Ans. FCFS

Q. What is network schema?

Q. Packet Burst is ______

Q. Picard's method uses _______?
Ans. Successive Differentiation.



The following are few sample questions that maybe asked in the hardware paper. We haven't been able to give the values in certain problems ; only the type of questions have been mentioned.

Q. Concentration and restivity is given and conductivity is asked for ?

Q. R , resistance and C, capacitance is given ,find the frequency and Q factor of the crystal ?

Q. Critical frequency and angle theta is given ;.the max useable frequency is to be calculated

Q. Questions on parabolic reflector antenna's and half wave dipole antenna's design

Q. Ramp signal is generated from integrator .Whether it is a low or high pass filter .?

Q. Calculate FM bandwidth given max modulation frequency FM , max freq deviation , df and 8 pairs allowable side band component ?

COBOL

COBOL QUESTION AND ANSWERS

1.The C language terminator is
a.semicolon
b.colon
c.period
d.exclamation mark
2.What is false about the following
A compound statement is
a.A set of simple statments
b.Demarcated on either side by curly brackets
c.Can be used in place of simple statement
d.A C function is not a compound statement.
3.What is true about the following
C Functions
a.Need not return any value
b.Should always return an integer
c.Should always return a float
d.Should always return more than one value.
4.Main must be written as
a.the first function in the program
b.Second function in the program
c.Last function in the program
d.any where in the program
5.Which of the following about automatic variables within a function
is correct ?
a.its type must be declared before using the variable
b.they are local
c.they are not initialised to zero
d.they are global.
6.Write one statement equalent to the following two statements
x=sqr(a);
return(x);
Choose from one of the alternatives
a.return(sqr(a));
b.printf("sqr(a)");
c.return(a*a*a);
d.printf("%d",sqr(a));
7.Which of the following about the C comments is incorrect ?
a.commentscan go over multiple lines
b.comments can start any where in the line
c.a line can contain comments with out any language statements
d.comments can occur within comments
8.What is the value of y in the following code?
x=7;y=0;
if(x=6)
y=7;
else
y=1;
a.7
b.0
c.1
d.6
9.Read the function conv() given below
conv(int t)
{
int u;
u=5/9 * (t-32);
return(u0;
}
What
a.15
b.0
c.16.1
d.29
10.which of the following represents true statement
either x is inthe range of 10 and 50 or y is zero
a.x>=10 && x<=50 || y==0;
b.
c.
d.
11.Which of the following is not an infinite loop ?
a.while(1){
....
}
b.for(;;){
...
}
c.x=0;
do{
/*x unaltered within theloop*/
...
}while(x==0);
d.# define TRUE 0
...
while(TRUE){
....
}
12.what does the following function print?
func(int i)
{
if(i%2)return 0;
eale return 1;
}
main()
{
int =3;
i=func(i);
i=func(i);
printf("%d",i);}
a.3
b.1
c.0
d.2
13.how does the C compiler interpret the following two statements
p=p+x;
q=q+y;
a.p=p+x;
q=q+y
b.p=p+xq=q+y
c.p=p+xq;
q=q+y
d.p=p+x/q=q+y

For questions 14,15,16,17 use the following alternatives

a.int
b.char
c.string
d.float
14.'9'
15."1 e 02"
16.10e05
17. 15

18.read the folllowing code
# define MAX 100
# define MIN 100
....
....
if(x>MAX)
x=1;
else if(x x=-1;
x=50;
if the initial value of x=200,what is the vlaue after executing this code?
a.200
b.1
c.-1
d.50
19.a memory of 20 bytes is allocated to a string declared as char *s
then the following two statements are executed:
s="Etrance"
l=strlen(s);
what is the value of l ?
a.20
b.8
c.9
d.21
20.given the piece of code
int a[50];
int *pa;
pa=a;
to access the 6th element of the array which of the following is incorrect?
a.*(a+5)
b.a[5]
c.pa[5]
d.*(*pa + 5)
21.consider the following structure:
struct num nam{
int no;
char name[25];
};
struct num nam n1[]={{12,"Fred"},{15,"Martin"},{8,"Peter"},{11,Nicholas"}};
.....
.....
printf("%d%d",n1[2],no,(*(n1 + 2),no) + 1);
What does the above statement print?
a.8,9
b.9,9
c.8,8
d.8,unpredictable value
22.identify the in correct expression
a.a=b=3=4;
b.a=b=c=d=0;
float a=int b=3.5;
d.int a;
float b;
a=b=3.5;
23.regarding the scope of the varibles;identify the incorrect statement:
a.automatic variables are automatically initialised to 0
b.static variables are are automatically initialised to 0
c.the address of a register variable is not accessiable
d.static variables cannot be initialised with any expression
24.cond 1?cond 2?cond 3?:exp 1:exp 2:exp 3:exp 4;
is equivalent to which of the following?
a.if cond 1
exp 1;
else if cond 2
exp 2;
else if cond 3
exp 3;
else
exp 4;
b.if cond 1
if cond 2
if cond 3
exp 1;
else
exp 2;
else
exp 3;
else
exp 4;
c.if cond 1 && cond 2 && cond 3
exp 1 |exp 2|exp 3|exp 4;
d.if cond 3
exp 1;
else if cond 2
exp 2;
else if cond 3
exp 3;
else
exp 4;
25.the operator for exponencation is
a.**
b.^
c.%
d.not available
26.which of the following is invalid
a.a+=b
b.a*=b
c.a>>=b
d.a**=b
27.what is y value of the code if input x=10
y=5;
if (x==10)
else if(x==9)
elae y=8;
a.9
b.8
c.6
d.7
28.what does the following code do?
fn(int n,int p,int r)
{
static int a=p;
switch(n){
case 4:a+=a*r;
case 3:a+=a*r;
case 2:a+=a*r;
case 1:a+=a*r;
}
}
a.computes simple interest for one year
b.computes amount on compound interest for 1 to 4 years
c.computes simple interest for four year
d.computes compound interst for 1 year
29.a=0;
while(a<5 br=""> printf("%d\n",a++);
how many times does the loop occurs?
a.infinite
b.5
c.4
d.6
30.how many times does the loop iterated ?
for (i=0;i=10;i+=2)
printf("Hi\n");
a.10
b.2
c.5
d.....
31.what is incorrect among teh following
A recursive functiion
a.calls itself
b.is equivalent to a loop
c.has a termination cond
d.does not have a return value at all
32.which of the following go out of the loopo if expn 2 becoming false
a.while(expn 1){...if(expn 2)continue;}
b.while(!expn 1){if(expn 2)continue;...}
c.do{..if(expn 1)continue;..}while(expn 2);
d.while(!expn 2){if(expn 1)continue;..}
33.consider the following program
B
main()
OB {unsigned int i=10;
while(i>=0){
printf("%u",i)
i--;
}
}
how many times the loop wxecuted
a.10
b.9
c.11
d.infinite
34.pick out the add one out
a.malloc()
b.calloc()
c.free()
d.realloc()
35.consider the following program
main()
{
int a[5]={1,3,6,7,0};
int *b;
b=&a[2];
}
the value of b[-1] is
a.1
b.3
c.-6
d.none
36.# define prod(a,b)=a*b
main()
{
int x=2;
int y=3;
printf("%d",prod(x+2,y-10)); }

the output of the program is
a.8
b.6
c.7
d.none
37.consider the following program sigment
int n,sum=1;
switch(n) {
case 2:sum=sum+2;
case 3:sum*=2;
break;
default:sum=0;}
if n=2, what is the value of sum
a.0
b.6
c.3
d.none
38.identify the incorrect one
1.if(c=1)
2.if(c!=3)
3.if(a
4.if(c==1)
a.1 only
b.1&3
c.3 only
d.all
39.teh format specified for hexa decimal is
a.%d
b.%o
c.%x
d.%u
40.find the output of the following program
main()
{
int x=5, *p;
p=&x;
printf("%d",++*p);
}
a.5
b.6
c.0
d.none
41.consider the following C code
main()
{
int i=3,x;
while(i>0)
{
x=func(i);
i--;
}
int func(int n)
{
static sum=0;
sum=sum+n;
return(sum);
}
the final value of x is
a.6
b.8
c.1
d.3
43.int *a[5] refers to
a.array of pointers
b.pointer to an array
c.pointerto a pointer
d......
46.which of the following statements is incorrect
a.typedef struct new{
int n1;
char n2;
} DATA;
b.typedef struct {
int n3;
char *n4;
}ICE;
c.typedef union {
int n5;
float n6;
} UDT;
d.#typedef union {
int n7;
float n8;
} TUDAT;

********************************************************************************
Only These Are The Questions Avilable For C Paper.

********************************************************************************
ANSWERS:
-----------

1-5 D,C,D,C,C

6-10 D,C,C,A,D

11-15 D,C,A,A,A

16-20 B,C,D,C,A

21-25 C,D,B,D,A

26-30 C,B,B,A,D

31-35 B,C,C,C,B

36-40 A,B,A,B,B

41-45 A,D,D,D,A

46-50 B,C,C,A,A


This the COBOL paper.

01.consider the following piece of code

01 GROSS-PAY
05 BASIC-PAY PIC 9(5)
05 ALLOWENCES PIC 9(3)
if BASIC-PAY has a value 1000 and ALLOWENCES has a value of 250,what will be
displayed by the statement
DISPLAY GROSS-PAY
a.1250
b.01000250
c.01250
d.1.250
02.consider two data items

77 W-A PIC 9(3)V99 VALUE 23.75
77 W-B PIC ZZ9V99 VLAUE 123.45
after the statement
MOVE W-A TO W-B
what will be W-B's value?
a.123.75
b.b23.75 (where b indicates space)
c.023.75
d.invalid move
03.what is the result of the following?

DIVIDE A INTO B GIVING C.

a.C=A/B
b.the reminder of B/A is stored in C
c.C=B/A
d.the reminder of A/B is stored in C
04.consider the statement (incomplete)
IF(A NUMERIC)
DISPLAY A
the variable A can be
a.NUMERIC
b.ALPHABETIC
c.ALPHANUMERIC
d.NUMERIC OR ALPHANUMERIC
05.which of the following can be used as a check protection symbol
a.Z
b.S
c.*
d.+
06.what if any ,is the syntex error in the following piece of code
01 B PIC A(7)
02 C PIC 9(4)
........
IF(B NUMERIC)
ADD 10 TO C
a.the condition in the if statement is wrong
b.noting is wrong
c.because C is initialised.ADD 10 TO C is wrong
d.both B and C shoud have same size.
07.study the following code
01 A1
05 B PIC 99
05 C PIC X(4)
01 A2
05 B PIC 99V99
05 C PIC A(4)
pick out the valid statement from the following
a.A1 and A2 can not have sub-ordinates
b.A1 and A2 can have the same sub-ordinates but must have same PIC clause
c.there is nothing wrong
d.A1 and A2 can have same sub-ordinates provided they are not at 01 level
08.study the following
01 A PIC 99V0 VALUE 5
01 B PIC 9V9 VALUE 6
01 C PIC 99V9 VALUE 2.5
01 D PIC 99 VALUE 3
COMPUTE A ROUNDED B C = A+B*C/D
ON SIZE ERROR PERFORM PRINT-ERROR
the comments of A.B.C after execution of the above statement are
a.A=10 B=0 C=10
b.A=10 B=9.9 C=9.9
c.A=10 B=0 C=9.9
d.A=10 B=6 C=10
09.how many times PARA-A is performed :
PERFORM PARA-A VARYING TIMES-COUNTER FROM 1 BY 1
UNTIL TIMES-COUNTER >0
PARA-A
MOVE P TO Q
MOVE H TO TIMES COUNTER
a.10
b.1
c.11
d.0
10.consider the following piece of code
01 GROUP-ITEM
05 AMOUNT-1 PIC 99V9 USAGE COMP VALUE 50
05 AMOUNT-2 PIC 9(4)V99 USAGE COMP
MOVE ZERO TO GROUP-ITEM
ADD 50 TO AMOUNT-1
what will be the content of AMOUNT-1?
a.50
b.100
c.0
d.unpredictable
11.consider the following progrm statements
MOVE 0 TO SW.NO.OF.REC
PERFORM PRI-OUT UNTIL SW=1
DISPALY NO.OF.REC
STOP RUN
PRE-OUT
READ IN-FILE AT END
MOVE 1 TO SW
WRITE OUO-REC FROM IN-REC
ADD 1 TO NO.OF REC
if the IN-FILE contains 1000 records what value will be displayedafter the
PERFORM is over?assume that N0.OF.REC has PIC 9(4)
a.1000
b.1001
c.1
d.none of the above since there is a syntex error
12.study the data discriptions and answer the questions given below
i)01 ORDER RECORD
05 OUT-HEADER PIC X(50)
05 ITEM-COUNT PIC 99
05 OUT-ITEM PIC X(20) OCCURS 1 TO 20 DEPENDING ON ITEM-COUNT
ii)01 NAME-AND-ADDRESS
05 N-AND-A-LINE OCCURES 5
05 LINE-LENGTH PIC P9
05 N-AND-A-CHAR PIC X OCCURS 1 TO 20 DEPENDING ON LINE-LENGTH
iii)01 SALES-LIST
05 SALESMAN-COUNT PIC 99
05 SALES PIC 9(6) OCCURS 1 TO 100 DEPENDING ON
SALESMAN-COUNT
iv)01 ORDER-RECORD
05 NO-OF-BRANDS PIC 99
05 BRAND-PURCHASED OCCURS 1 TO 15 DEPENDING ON NO-OF-BRANDS
which of the following is true?
a.i) and iii) are valid
b.i) and iv) are valid
c.i) and iii) are not valid
d.all are valid
13.C1 C2 C3 are three conditions whose TRUTH values are as folloes.
C1-TRUE C2-FALSE C3-TRUE
A,B,C are defined as given below
A:C1 AND(NOT C2) OR C3
B.(NOT C1) OR (NOT C2 AND NOT C3)
C.(C1 OR C2)AND C3
D.C1 AND C2 OR C3
given the above information which of the following statements are valid?
a.only A,B and C are TRUE
b.only A,C and D are TRUE
c.A,B,C and D are TRUE
d.only C and D are TRUE
14.consider the following
FD FILE-1
01 REC-1 PIC X(80)
......
WORKING-STORAGE SECTION
01 W-REC PIC X(90)
........
PROCEDURE DIVISION
FIRST-PARA
.......
READ FILE-1 INTO W-REC AT END MOVE 1 TO EOF-FLAG
which of the following is true with respect to the above?
a.REC-1 will contain nothing and W-REC will contain the contains of the
record read
b.REC-1 and W-REC contain the same data
c.syntex is invalid and error will occur
d.REC-1 and W-REC must be of same size
15.PERFORM ACCUMULATE-TOTALS
VARYING A FROM 1 BY 2 UNTIL A >2
AFTER B FROM1 BY 1 UNTIL B>2
AFTER C FROM 2 BY -1 UNTIL C<2 br=""> the paragraph ACCUMULATE-TOTALS would be exicuted
a.18 times
b.4 times
c.8 times
d.24 times
16.there is a file whose ORGANISATION is INDEXED.you want to read the records
from the file in RANDOM fashion as well as sequentially.then which of the
access mode would you specify?
a.SEQUENTIAL
b.RANDOM
c.DYNAMIC
D.ACCESS MODE has nothing to do with it
17.consider the following PROCEDURE DIVISION entry
OPEN EXTEND IN-FILE
identify the correct statement
a.organization of IN-FILE is sequential and records can be added in the
beginning
b.organization of IN-FILE is sequential and records can be added in the
end
c.organization of IN-FILE is indexed and records can be added in the
beginning
d.organization of IN-FILE is indexed and records can be added in the end
18.what is the size of W-REC in the following
01 W-REC
05 A PIC 9(4)V99
05 B READLINES A
10 C PIC XX
10 D PIC S9(4)
05 E OCCURS 7 PIC ZZ.ZZ
05 F OCCURS 5
10 G PIC ZZ.ZZZ99
10 H OCCURS 3
15 J PIC 9(3)
15 K PIC V99
a.177
b.161
c.180
d.none of yhe above
19.consider the following two IF statements:
IF X AND NOT Y MOVE A TO B
IF Z=1 OR 9 MOVE A TO B
select one of the following data divusion entries which gives identical
results for both the above IF statements
a.01 Z PIC 9
88 X VALUE 1.9
88 Y VALUE 0.2 THRU 8
b.01 Z PIC 9
88 X VALUE 0.2 THRU 8
Y VALUE 1.9
c.01 Z PIC 9
88 X VALUE 1.9
88 NOT-Y VALUE 0.2 THRU 1.9
d.none of yhe above
20.consider the following two statements
MOVE 10 TO N
PERFORM PARA-X N TIMES
STOP RUN
PARA-X
MOVE 5 TO N
how many times PARA-X willbe exicuted?
a.10
b.5
c.infinate
d.execution error
21.given the following:
77 A PIC 9V9 VALUE 9.5
77 B PIC 9 VALUE 9.
77 C PIC V9 VALUE 0.8
77 D PIC 9
77 E PIC 9
77 F PIC 9V999
what are the contenta of D E nad F after teh following statements are
executed:
COMPUTE F ROUNDED=A+C/B
MULTIPLY A BY C GIVING E
ADD B C A GIVING D ROUNDED
a.F=9.589 E=8 D=1
b.F=9.589 E=8 D=9
c.F=9.589 E=7 D=9
d.F=9.589 E=7 D=1

22. Consider the follwoing IF condition:

IF A LESS 1200 IF B GREATER 25 MOVE 47 TOC
ELSE MOVE 57 TO C
IF A GREATER 249 MOVE 67 TO C
ELSE NEXT SENTENCE ELSE IF B LESS 67
MOVE 27 TO C

What will be the value of C, when A is 137 and b is 25
(a) 27
(b) 57
(c) 67
(d) none

23. Consider the following:

77 W-NUM PIC 9 VALUE 0
------
MOVE 1 TO W-NUM
PERFORM PARA-X UNTIL W-NUM > 9.
------
PARA-X
ADD 1 TO W-NUM

How many times PARA-X is executed ?
(a) 10
(b) 9
(c) 11
(d) Infinite loop

24. Consider the following code:

77 A PIC 99V99 VALUE 55.35
77 B PIC 99V999 VALUE 32.754

ADD B TO A ON SIZE ERROR DISPLAY "ERROR!!!"

What will be the result ?
(a) A=88.10, B=32.754
(b) A=87.00 B=32.754
(c) A=87.10 B=32.754
(d) ERROR!!! will be DISPLAYed on the screen.

25. Consider the following:

77 A PIC 9(10)
77 B PIC 9(10)
77 C PIC 9(19)

MULTIPLY AB BY B GIVING C

Which of the following is true ?

(a) The execution of the above may result in size error.
(b) The execution of the above will result in size error.
(c) The definition of C is invalid resulting in compilation error.
(d) No error will be thee and the program would proceed correctly.

26. A paragraph PARA-X is to be executed when none oof the data names
A, B and C have value of 1. Which of the following will achieve this ?

(a) IF A NOT = 1 OR B NOT = 1 OR C NOT = 1 PERFORM PARA-X
(B) IF NOT A= 1 AND B= 1 AND C = 1 PERFORM PARA-X
(C) IF A NOT =1 IF NOT B = 1 OR C= 1 PERFORM PARA-X
(C) IF A NOT = 1 AND B NOT = 1 AND C NOT = 1 PERFORM PARA-X



27. Study the five expressions and the class to which they belong:
S.N. Expression Class
1 "SPACES" Figurative constant
2. "Depreciation Schedule Non-numeric literal
3. "12%" Non-numeric literal
4. INTEREST-DUE Non-numeric literal
5. ZEROES Figurative constant
Which of the following statement is true?
(a) 1 and 3 are incorrect
(b) 1 and 4 are incorrect
(c) 3 and 4 are incorrect
(d) All are correct

28. Identify the invalid dataname from the following:
(a) SAVINGS-ACCOUNT
(b) ANNUAL-ALLOCATION-FOR-OVERHEAD
(c) SAMOUNT250
(d) 12DEMAND

29. Study the DATA DIVISION entries and the three PROCEDURE DIVISION entries
given below:
01 END-OF-FILE-SWITCH PIC XXX.
88 NO-MORE-RECS VALUE "YES".
88 MORE-RECS VALUE "NO".
(i) READ SAMPLE-FILE AT END MOVE "YES" TO NO-MORE-RECS.
(ii) IF NO-MORE-RECS = "YES" GO TO LAST-PARA.
(iii) IF NO-MORE-RECS GO TO LAST-PARA.
Which are wrong?
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) all

30. The following entries appear in the WORKING-STORAGE SECTION:
01 DATE-TODAY.
05 YY PIC XX VALUE "90".
05 MM PIC XX VALUE "12".
05 DD PIC XX VALUE :31".
01 DATE-EDIT PIC XX/XX/XX.
MOVE DATE-TODAY TO DATE-EDIT.
(a) 901231
(b) 90/12/31
(c) 31/12/90
(d) 311290

31. How many bytes will be allocated for the following record description
entries?
01 REC-A.
05 A PIC S9(4).
05 B PIC XXXBXXX.
05 C PIC ____9.99.
05 D PIC S9(5) COMP-3.
05 E PIC 9(3) COMP.
(a) 29
(b) 26
(c) 25
(d) 28

32. What is wrong with the following data declaration?
01 W-DATE PIC X(6).
05 DD PIC 99.
05 MM PIC 99.
05 YY PIC 99.
(a) Nothing is wrong.
(b) Under W-DATE all level 05 items are having a PIC 99 but level
01 has PIC X(6).
(c) PIC can't be specified for a group item.
(d) DD, MM, and YY are invalid datanames.

33. What is the output generated by the following code?
01 GRP-I.
05 SUBFLD1 PIC XX VALUE "AB".
05 FILTER PIC X(6) VALUE SPACES.
01 GRP-2 REDEFINED GRP-1.
05 SUB-FLD2 PIC XX.
05 SUB-FLD3 PIC XX.
05 FILTER PIC X(4).
IF SUB-FLD1 NOT = SPACES
DISPLAY "SUBFLD1"
MOVE "ABBCCD" TO GRP-1
IF SUB-FLD3 = SPACES
DISPLAY "SPACES"
ELSE
DISPLAY "SUBFLD3"
DISPLAY "END"
ELSE
DISPLAY "SPACES"
DISPLAY "END".
(a) SUBFLD1
SUBFLD3
END
(b) SPACES
END
(c) SUBFLD1
END
(d) SUBFLD1
SPACES

34. 88 level entry is used for
(a) data items in WORKING-STORAGE SECTION
(b) items with RENAMES clause
(c) condition-names
(d) None of the above

35. ZEROES and SPACES are _______ constants
(a) Figurative
(b) Numeric
(c) Non-numeric
(d) Alphabete

36. COMPUTE X = A * B - C * D and
COMPUTE X = (A * B) - (C * D)
(a) Are not the same
(b) Are same
(c) Syntactically wrong
(d) Will yield a run time error

37. OCCURS clause is used in the DATA DIVISION on data names at
(a) 01 level
(b) 77 level
(c) 88 level
(d) any level from 02 to 49

38. Consider the following COBOL entries:
05 X PIC 99 VALUE 10.
SUBTRACT 20 FROM X.
The resultant value of X wil be
(a) 10
(b) 00
(c) compile-time error
(d) none of these

39. Consider the following COBOL entries
05 X PIC 99 VALUE 10.
ADD 40 X TO X.
COMPUTE X = 3 * X - 40.
The result in X is
(a) 10
(b) 40
(c) Compile or Run time error
(d) none of these

40. given the following piece of code:
CALL SUB-PGM USING A, B, C.
CALL SUB-PGM USING A, C, C.
(a) Both CALL statements will always produce same result.
(d) Both CALL statements may produce different result.
(c) Compile-time error because SUB-PGM is a dataname.
(d) Compile-time error because A, B, C are used twice.

41. The hierarchy of the execution of logical operators is
(a) NOT AND OR
(b) AND OR NOT
(c) OR AND NOT
(d) OR NOT AND

42. The order of precedence of arithmetic operators in an expression can be
overridden with the use of
(a) []
(b) ()
(c) {}
(d) Any of the above

Consider the following passage for answering questions 43 to 47.

A program is written to accept an answer to the query "enough fo the Day?"
If the respons is "N" then the program accepts quantity purchased and rate
of the item and displays the amount to be collected. Then the above query
is again displayed and the loop continues. At the end of the day, when
the response to the above query is "Y", the day collections are displayed.

The program checks that the quantity purchased is between 25 and 125 and the
rate of the item is between 10.00 and 75.00. If any of these two conditions
are violated, the program displays an appropriate message and asks for next
input. The amounts are displayed with proper editing. The program is written
assuming that there can be a maximum of 1000 transactions a day.

43. How many variables would you declare for the above problem?
(a) 3
(b) 4
(c) 5
(d) 7

44. What should be the PICTURE clause of the variable used to calculate
end of the day collections?
(a) 9(9)v99
(b) 9(8)v99
(c) 995)v99
(d) Information given is insufficient to arrive at the answer

45. What should be the PICTURE clause of the variable used to calculate
to be collected.
(a) 9(9)v99
(b) 9(8)v99
(c) 9(5)v99
(d) Information given is insufficient to arrive at the answer

46. Assuming that the above program is being executed in a Department
Stores in MADRAS which of the following PICTURE clause will be
suitable for DISPLAYing the end of the day collections?
(a) Z(5)V99
(b) Z(5).99
(c) ZZ,ZZ,ZZ,ZZ9.99
(d) Information given is insufficient to arrive at the answer

47. How many _____ statements do you think will be there in the program?
(a) 3
(b) 4
(c) 5
(d) Information given is insufficient to arrive at the answer

48. Which of the following paragraphs is compulsory in every COBOL program?
(a) SPECIAL-NAMES
(b) PROGRAM-ID
(c) FILE-CONTROL
(d) OBJECT-COMPUTER

49. Which of the following files can be OPENed in all the 4 modes? The four
modes are INPUT, I-O, OUTPUT and EXTEND.
(a) INDEXED
(b) RELATIVE
(c) SEQUENTIAL
(d) All of the above

50. Which of the following EDITind and PICTURE symbols is to be used if a
minus(-) is to appear before the value if the value is -ve and a plus(+)
is to appear before the value if the value is +ve?
(a) +
(b) -
(c) + OR
(d) It is not possible

solutions

b,b,c,c,c,a,d,a,b,a,c,c,b,b,b,c,b,d,a,a,c,b,d,a,d,d,b,c,d,b,a,c,a,c,a,b,d,
a,c,b,a,b,b,b,c,c,a,b,c,a

C LANGUAGE INTERVIEW QUESTIONS

C LANGUAGE INTERVIEW QUESTIONS
1.What does static variable means?

2.What is a Pointer?
3.What is a Structure?
4.What are the differences between Structures and Arrays?
5.In header files whether functions are declared or defined?
6.What are the differences between malloc() and calloc()?
7.What are Macros? What are its advantages and disadvantages?
8.Difference between Pass by Value and Pass by reference?
9.What is static identifier?
10.Where is the auto variables stored?
11.Where does global, static, local, register variables, free memory and C program instructions get stored?
12.Difference between arrays and linked list?
13.What are enumerations?
14.Describe about storage allocation and scope of global, extern, static, local and register variables?
15.What are register variables? What are the advantages of using it?
16.What is the use of typedef?
17.Can we specify variable field width in a scanf()format string? If possible, how?
18.Out of fgets() and gets(), which function is safe to use and Why?
19.Difference between strdup and strcpy?
20.What is recursion?
21.Differentiate between a FOR loop and a WHILE loop? What are its uses?
22.What are the different storage classes in C?
23.Write down the equivalent pointer expression for referring the same element a[i][j][k][l]?
24.What is the difference between Structure and Unions?
25.What are the advantages of using Unions?
26.What are the advantages of using pointers in a program?
27.What is the difference between Strings and Arrays?
28.What is a far pointer? Where we use it?
29.How will you declare an array of three function pointers where each function receives two int and returns a float?
30.What is NULL pointer? Whether it is same as an un-initialized pointer?
31.What is a NULL macro? What is the difference between a NULL pointer and a NULL macro?
32.What does the error ‘Null Pointer Assignment’ means and what causes this error?
33.What is near, far and huge pointers? How many bytes are occupied by them?
34.How would you obtain segment and offset addresses from a far address of a memory location?
35.Are the expressions arr and &arr same for an array of integers?
36.Does mentioning the array name gives the base address in all the contexts?
37.Explain one method to process an entire string as one unit?
38.What is the similarity between a Structure, Union and Enumeration?
39.Can a Structure contain a Pointer to itself?
40.How can we check whether the contents of two structure variables are same or not?
41.How are Structure passing and returning implemented by the compiler?
42.How can we read/write Structures from/to data files?
43.What is the difference between an enumeration and a set of pre-processor # defines?
44.What do the ‘c’ and ‘v’ in argc and argv stand for?
45.What is the maximum combined length of command line arguments including the space between adjacent arguments?
46.If we want that any wildcard characters in the command line arguments should be appropriately expanded, are we required to make any special provision? If yes, which?
47.Does there exist any way to make the command line arguments available to other functions without passing them as arguments to the function?
48.What are bit fields?
49.What is the use of bit fields in a Structure declaration?
50.To which numbering system can the binary number 1101100100111100 be easily converted to?
51.Which bit wise operator is suitable for checking whether a particular bit is on or off?
52.Which bit wise operator is suitable for turning off a particular bit in a number?
53.Which bit wise operator is suitable for putting on a particular bit in a number?
54.Which one is equivalent to multiplying by 2: Left shifting a number by 1 or Left shifting an unsigned int or char by 1?
55.Write a program to compare two strings without using the strcmp() function?
56.Write a program to concatenate two strings?
57.Write a program to interchange 2 variables without using the third one?
58.Write a program for String Reversal?
59.Write a program for Palindrome check?
60.Write a program to find the Factorial of a number?
61.Write a program to generate Fibonacci series?
62.Write a program which employs Recursion?
63.Write a program which uses Command Line Arguments?
64.Write a program which uses functions like strcmp(), strcpy(), etc.?
65.What are the advantages of using typedef in a program?
66.How would you dynamically allocate a one-dimensional and two-dimensional array of integers?
67.When reallocating memory if nay other pointers point the same piece of memory, do you have to readjust these other pointers or do they get readjusted automatically?
68.Which function should be used to free the memory allocated by calloc()?
69.How much maximum can you allocate in a single call to malloc()?
70.Can you dynamically allocate arrays in expanded memory?
71.What is object file? How can you access object file?
72.Which header file should include if you are to develop a function which can accept variable number of arguments?
73.Can you write a function similar to printf()?
74.How can a called function determine the number of arguments that have been passed to it?
75.Can there be at least some solution to determine the number of arguments passed to a variable argument list function?
76.How do you declare, An array of three pointers to chars?
77.How do you declare, An array of three char pointers?
78.How do you declare, A pointer to array of three chars?
79.How do you declare, A pointer to function which receives an int pointer and returns a float pointer?
80.How do you declare, A pointer to a function which receives nothing and returns nothing?
81.What do the functions atoi(), itoa() and gcvt() do?
82.Does there exist any other function which can be used to convert an integer or a float to a string?
83.How would you use qsort() function to sort an array of structures?
84.How would you use qsort() function to sort the name stored in an array of pointers to string?
85.How would you use bsearch() function to search a name stored in array of pointers to string?
86.How would you use the functions sin(), pow(), sqrt()?
87.How would you use the functions memcpy(), memset(), memmove()?
88.How would you use the functions fseek(), fread(),fwrite() and ftell()?
89.How would you use the functions randomize() and random()?
90.How would you obtain current time and difference between two times?
91.How would you implement a substr() function that extracts a sub string from a given string?
92.What is the difference between the functions rand(), random(), srand() and randomize()?
93.What is the difference between the functions memmove() and memcpy()?
94.How do you print a string on the printer?
95.Can you use the function fprintf() to display the output on the screen?

TECHINICAL BIO DATA


Multithreading
The ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other

Hyper-Threading
A technology developed by Intel that enables multithreaded software applications to execute threads in parallel on a single multi-core processor instead of processing threads in a linear fashion. Older systems took advantage of dual-processing threading in software by splitting instructions into multiple streams so that more than one processor could act upon them at once

thread

(1) In online discussions, a series of messages that have been posted as replies to each other. A single forum or conference typically contains many threads covering different subjects. By reading each message in a thread, one after the other, you can see how the discussion has evolved. You can start a new thread by posting a message that is not a reply to an earlier message.
(2) In programming, a part of a program that can execute independently of other parts. Operating systems that support multithreading enable programmers to design programs whose threaded parts can execute concurrently.

operating system

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.
Operating systems can be classified as follows:
multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.
multiprocessing : Supports running a program on more than one CPU.
multitasking : Allows more than one program to run concurrently.
multithreading : Allows different parts of a single program to run concurrently.
real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.
Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.
As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.

multiprocessing

(1) Refers to a computer system's ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently. UNIX is one of the most widely used multiprocessing systems, but there are many others, including OS/2 for high-end PCs. Multiprocessing systems are much more complicated than single-process systems because the operating system must allocate resources to competing processes in a reasonable manner.
(2) Refers to the utilization of multiple CPUs in a single computer system. This is also called parallel processing.
parallel processing

The simultaneous use of more than one CPU to execute a program. Ideally, parallel processing makes a program run faster because there are more engines (CPUs) running it. In practice, it is often difficult to divide a program in such a way that separate CPUs can execute different portions without interfering with each other.
Most computers have just one CPU, but some models have several. There are even computers with thousands of CPUs. With single-CPU computers, it is possible to perform parallel processing by connecting the computers in a network. However, this type of parallel processing requires very sophisticated software called distributed processing software.
Note that parallel processing differs from multitasking, in which a single CPU executes several programs at once.
Parallel processing is also called parallel computing.

distributed processing
Refers to any of a variety of computer systems that use more than one computer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU to execute programs. More often, however, distributed processing refers to local-area networks (LANs) designed so that a single program can run simultaneously at various sites. Most distributed processing systems contain sophisticated software that detects idle CPUs on the network and parcels out programs to utilize them.
Another form of distributed processing involves distributed databases, databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

multitasking

The ability to execute more than one task at the same time, a task being a program. The terms multitasking and multiprocessing are often used interchangeably, although multiprocessing implies that more than one CPU is involved.
In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time.
There are two basic types of multitasking: preemptive and cooperative. In preemptive multitasking, the operating system parcels out CPU time slices to each program. In cooperative multitasking, each program can control the CPU for as long as it needs it. If a program is not using the CPU, however, it can allow another program to use it temporarily. OS/2, Windows 95, Windows NT, the Amiga operating system and UNIX use preemptive multitasking, whereas Microsoft Windows 3.x and the MultiFinder (for Macintosh computers) use cooperative multitasking.

cooperative multitasking

A type of multitasking in which the process currently controlling the CPU must offer control to other processes. It is called cooperative because all programs must cooperate for it to work. If one program does not cooperate, it can hog the CPU. In contrast, preemptive multitasking forces applications to share the CPU whether they want to or not. Versions 8.0-9.2.2 of Macintosh OS and Windows 3.x operating systems are based on cooperative multitasking, whereas UNIX, Windows 95, Windows NT, OS/2, and later versions of Mac OS are based on preemptive multitasking

semaphore
A hardware or software flag. In multitasking systems, a semaphore is a variable with a value that indicates the status of a common resource. It's used to lock the resource that is being used. A process needing the resource checks the semaphore to determine the resource's status and then decides how to proceed.

deadlock
A condition that occurs when two processes are each waiting for the other to complete before proceeding. The result is that both processes hang. Deadlocks occur most commonly in multitasking and client/server environments. Ideally, the programs that are deadlocked, or the operating system, should resolve the deadlock, but this doesn't always happen.
A deadlock is also called a deadly embrace.


The 7 Layers of the OSI Model

The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
Application

(Layer 7) This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.
Presentation
(Layer 6) This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
Session
(Layer 5) This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
Transport
(Layer 4) This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
Network
(Layer 3) This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

Data Link
(Layer 2) At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.


Physical
(Layer 1) This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

applet
A program designed to be executed from within another application. Unlike an application, applets cannot be executed directly from the operating system. With the growing popularity of OLE (object linking and embedding), applets are becoming more prevalent. A well-designed applet can be invoked from many different applications.
Web browsers, which are often equipped with Java virtual machines, can interpret applets from Web servers. Because applets are small in files size, cross-platform compatible, and highly secure (can't be used to access users' hard drives), they are ideal for small Internet applications accessible from a browser.

J2EE

Short for Java 2 Platform Enterprise Edition. J2EE is a platform-independent, Java-centric environment from Sun for developing, building and deploying Web-based enterprise applications online. The J2EE platform consists of a set of services, APIs, and protocols that provide the functionality for developing multitiered, Web-based applications.
Some of the key features and services of J2EE:
At the client tier, J2EE supports pure HTML, as well as Java applets or applications. It relies on Java Server Pages and servlet code to create HTML or other formatted data for the client.
Enterprise JavaBeans (EJBs) provide another layer where the platform's logic is stored. An EJB server provides functions such as threading, concurrency, security and memory management. These services are transparent to the author.
Java Database Connectivity (JDBC), which is the Java equivalent to ODBC, is the standard interface for Java databases.
The Java servlet API enhances consistency for developers without requiring a graphical user interface.

MAC Layer
The Media Access Control Layer is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC) to another across a shared channel.
See a breakdown of the seven OSI layers in the Quick Reference section of Webopedia.
The MAC sublayer uses MAC protocols to ensure that signals sent from different stations across the same channel don't collide.
Different protocols are used for different shared networks, such as Ethernets, Token Rings, Token Buses, and WANs.
flow control
(1) In communications, the process of adjusting the flow of data from one device to another to ensure that the receiving device can handle all of the incoming data. This is particularly important where the sending device is capable of sending data much faster than the receiving device can receive it.
There are many flow control mechanisms. One of the most common flow control protocols for asynchronous communication is called xon-xoff. In this case, the receiving device sends a an xoff message to the sending device when its buffer is full. The sending device then stops sending data. When the receiving device is ready to receive more data, it sends an xon signal.
Flow control can be implemented in hardware or software, or a combination of both.
(2) In programming, the statements and other constructs that control the order in which operations are executed. For example, common looping statements such as for…next and while are known as flow control statements. Branching statements, such as if…then are also part of a programming language's flow control mechanism.

100Base-T
A networking standard that supports data transfer rates up to 100 Mbps (100 megabits per second). 100BASE-T is based on the older Ethernet standard. Because it is 10 times faster than Ethernet, it is often referred to as Fast Ethernet. Officially, the 100BASE-T standard is IEEE 802.3u.
Like Ethernet, 100BASE-T is based on the CSMA/CD LAN access method. There are several different cabling schemes that can be used with 100BASE-T, including:
Telnet
(tel´net) (n.) A terminal emulation program for TCP/IP networks such as the Internet. The Telnet program runs on your computer and connects your PC to a server on the network. You can then enter commands through the Telnet program and they will be executed as if you were entering them directly on the server console. This enables you to control the server and communicate with other servers on the network. To start a Telnet session, you must log in to a server by entering a valid username and password. Telnet is a common way to remotely control Web servers.

CSMA/CD
Short for Carrier Sense Multiple Access / Collision Detection, a set of rules determining how network devices respond when two devices attempt to use a data channel simultaneously (called a collision). Standard Ethernet networks use CSMA/CD. This standard enables devices to detect a collision. After detecting a collision, a device waits a random delay time and then attempts to re-transmit the message. If the device detects a collision again, it waits twice as long to try to re-transmit the message. This is known as exponential back off.
CSMA/CD is a type of contention protocol.

distributed processing
Refers to any of a variety of computer systems that use more than one computer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU to execute programs. More often, however, distributed processing refers to local-area networks (LANs) designed so that a single program can run simultaneously at various sites. Most distributed processing systems contain sophisticated software that detects idle CPUs on the network and parcels out programs to utilize them.
Another form of distributed processing involves distributed databases, databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.

FTP
Short for File Transfer Protocol, the protocol for exchanging files over the Internet. FTP works in the same way as HTTP for transferring Web pages from a server to a user's browser and SMTP for transferring electronic mail across the Internet in that, like these technologies, FTP uses the Internet's TCP/IP protocols to enable data transfer.
FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a Web page file to a server).

TCP/IP

(pronounced as separate letters) Short for Transmission Control Protocol/Internet Protocol, the suite of communications protocols used to connect hosts on the Internet. TCP/IP uses several protocols, the two main ones being TCP and IP. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as Netware, also support TCP/IP.

switch
(1) In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.
(2) A small lever or button. The switches on the back of printers and on expansion boards are called DIP switches. A switch that has just two positions is called a toggle switch.
(3) Another word for option or parameter -- a symbol that you add to a command to modify the command's behavior.

protocol
An agreed-upon format for transmitting data between two devices. The protocol determines the following:
the type of error checking to be used
data compression method, if any
how the sending device will indicate that it has finished sending a message
how the receiving device will indicate that it has received a message
There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others, some are more reliable, and some are faster.
From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. The protocol can be implemented either in hardware or in software.

HTTP
Short for HyperText Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.
The other main standard that controls how the World Wide Web works is HTML, which covers how Web pages are formatted and displayed.
HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it. This is the main reason that it is difficult to implement Web sites that react intelligently to user input. This shortcoming of HTTP is being addressed in a number of new technologies, including ActiveX, Java, JavaScript and cookies.
Also see The Difference Between FTP and HTTP in the Did You Know . . . ? section of Webopedia.

SMTP
(pronounced as separate letters) Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.

routing
(n.) In internetworking, the process of moving a packet of data from source to destination. Routing is usually performed by a dedicated device called a router. Routing is a key feature of the Internet because it enables messages to pass from one computer to another and eventually reach the target machine. Each intermediary computer performs routing by passing along the message to the next computer. Part of this process involves analyzing a routing table to determine the best path.
Routing is often confused with bridging, which performs a similar function. The principal difference between the two is that bridging occurs at a lower level and is therefore more of a hardware function whereas routing occurs at a higher level where the software component is more important. And because routing occurs at a higher level, it can perform more complex analysis to determine the optimal path for the packet.
An application that runs on a personal computer or workstation and enables you to send, receive and organize e-mail. It's called a client because e-mail systems are based on a client-server architecture. Mail is sent from many clients to a central server, which re-routes the mail to its intended destination.

The Difference Between FTP and HTTP


File Transfer Protocol, or FTP, is a protocol used to upload files from a workstation to a FTP server or download files from a FTP server to a workstation. It is the way that files get transferred from one device to another in order for the files to be available on the Internet. When ftp appears in a URL it means that the user is connecting to a file server and not a Web server and that some form of file transfer is going to take place. Most FTP servers require the user to log on to the server in order to transfer files.
In contrast, Hyper Text Transfer Protocol, or HTTP, is a protocol used to transfer files from a Web server onto a browser in order to view a Web page that is on the Internet. Unlike FTP, where entire files are transferred from one device to another and copied into memory, HTTP only transfers the contents of a web page into a browser for viewing. FTP is a two-way system as files are transferred back and forth between server and workstation. HTTP is a one-way system as files are transported only from the server onto the workstation's browser. When http appears in a URL it means that the user is connecting to a Web server and not a file server. The files are transferred but not downloaded, therefore not copied into the memory of the receiving device.

Web server
A computer that delivers (serves up) Web pages. Every Web server has an IP address and possibly a domain name. For example, if you enter the URL http://www.pcwebopedia.com/index.html in your browser, this sends a request to the server whose domain name is pcwebopedia.com. The server then fetches the page named index.html and sends it to your browser.
Any computer can be turned into a Web server by installing server software and connecting the machine to the Internet. There are many Web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others.

gateway

(n.) (1) A node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet.
In enterprises, the gateway node often acts as a proxy server and a firewall. The gateway is also associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway.
(2) A computer system located on earth that switches data signals and voice signals between satellites and terrestrial networks.
(3) An earlier term for router, though now obsolete in this sense as router is commonly used

ActiveX control
A control using ActiveX technologies. An ActiveX control can be automatically downloaded and executed by a Web browser. ActiveX is not a programming language, but rather a set of rules for how applications should share information. Programmers can develop ActiveX controls in a variety of languages, including C, C++, Visual Basic, and Java.
An ActiveX control is similar to a Java applet. Unlike Java applets, however, ActiveX controls have full access to the Windows operating system. This gives them much more power than Java applets, but with this power comes a certain risk that the applet may damage software or data on your machine. To control this risk, Microsoft developed a registration system so that browsers can identify and authenticate an ActiveX control before downloading it. Another difference between Java applets and ActiveX controls is that Java applets can be written to run on all platforms, whereas ActiveX controls are currently limited to Windows environments.
Related to ActiveX is a scripting language called VBScript that enables Web authors to embed interactive elements in HTML documents.

platform
The underlying hardware or software for a system. For example, the platform might be an Intel 80486 processor running DOS Version 6.0. The platform could also be UNIX machines on an Ethernet network.
The platform defines a standard around which a system can be developed. Once the platform has been defined, software developers can produce appropriate software and managers can purchase appropriate hardware and applications. The term is often used as a synonym of operating system.
The term cross-platform refers to applications, formats, or devices that work on different platforms. For example, a cross-platform programming environment enables a programmer to develop programs for many platforms at once.

script
Another term for macro or batch file, a script is a list of commands that can be executed without user interaction. A script language is a simple programming language with which you can write scripts.
Apple Computer uses the term script to refer to programs written in its HyperCard or AppleScript language.
Application Server -
A software program that handles all application operations between users and an organization's backend business applications or databases. Application servers are typically used for complex transaction-based applications. To support high-end needs, an application server has to have built-in redundancy, monitors for high-availability, high-performance distributed application services and support for complex database access. These are the leading Java App Servers:
Apache/Jakarta Tomcat (the open source, and official reference implementation of the Java Servlet and JSP technologies) BEA WebLogic IBM WebSphere iPlanet Application Server Oracle Application Server
Enterprise JavaBeans (EJB) - A Java API developed by Sun Microsystems that defines a component architecture for multi-tier client/server systems. EJB systems allow developers to focus on the actual business architecture of the model, rather than worry about endless amounts of programming and coding needed to connect all the working parts. This task is left to EJB server vendors. Developers just design (or purchase) the needed EJB components and arrange them on the server. Because EJB systems are written in Java, they are platform independent. Being object oriented, they can be implemented into existing systems with little or no recompiling and configuring. (from Webopedia)
Java - A high-level object-oriented programming language developed by Sun Microsystems. Java is similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT).
Java 2 Platform Enterprise Edition (J2EE) - J2EE is a platform-independent, Java-centric environment from Sun for developing, building and deploying Web-based enterprise applications online. The J2EE platform consists of a set of services, APIs, and protocols that provide the functionality for developing multitiered, Web-based applications.

Java Applet - A program designed to be executed from within another application. Unlike an application, applets cannot be executed directly from the operating system. Applets became more prevalent with the popularity growth of OLE (object linking and embedding). A well-designed applet can be invoked from many different applications. Web browsers, which are often equipped with Java virtual machines, can interpret applets from Web servers. Because applets are small in file size, cross-platform compatible, and highly secure (can't be used to access users' hard drives), they are ideal for small Internet applications accessible from a browser. (from Webopedia)

Java Beans - A specification developed by Sun Microsystems that defines how Java objects interact. An object that conforms to this specification is called a JavaBean, and is similar to an ActiveX control. It can be used by any application that understands the JavaBeans format. The principal difference between ActiveX controls and JavaBeans are that ActiveX controls can be developed in any programming language but executed only on a Windows platform, whereas JavaBeans can be developed only in Java, but can run on any platform. (from Webopedia)




Java Database Connectivity (JDBC) - A Java API that enables Java programs to execute SQL statements. This allows Java programs to interact with any SQL-compliant database. Since nearly all relational database management systems (DBMSs) support SQL, and because Java itself runs on most platforms, JDBC makes it possible to write a single database application that can run on different platforms and interact with different DBMSs. (from Webopedia)

Java Server Pages (JSP) - A server-side technology that serve as an extension to the Java servlet technology that was developed by Sun as an alternative to Microsoft's ASPs (Active Server Pages). JSPs have dynamic scripting capability that works in tandem with HTML code, separating the page logic from the static elements -- the actual design and display of the page. Embedded in the HTML page, the Java source code and its extensions help make the HTML more functional, being used in dynamic database queries, for example. JSPs are not restricted to any specific platform or server. (from Webopedia)

Java Servlet - An applet that runs on a server. The term usually refers to a Java applet that runs within a Web server environment. This is analogous to a Java applet that runs within a Web browser environment. Java servlets are becoming increasingly popular as an alternative to CGI programs. The biggest difference between the two is that a Java applet is persistent. This means that once it is started, it stays in memory and can fulfill multiple requests. In contrast, a CGI program disappears once it has fulfilled a request. The persistence of Java applets makes them faster because there's no wasted time in setting up and tearing down the process. (from Webopedia)

macro
(1) A symbol, name, or key that represents a list of commands, actions, or keystrokes. Many programs allow you to create macros so that you can enter a single character or word to perform a whole series of actions. Suppose, for example, that you are editing a file and want to indent every third line five spaces. If your word processor supports macros, you can create one that consists of the following keystrokes:
Move Cursor to Beginning of Line
Move Cursor Down 1 Line
Move Cursor Down 1 Line
Move Cursor Down 1 Line
Insert 5 Spaces
Now you can enter the name of the macro, and the word processor will perform all these commands at once.
You can also use macros to enter words or phrases that you use frequently. For example, you could define a macro to contain all the keystrokes necessary to begin a letter -- your name, address, and a code that inserts the current date. Then, whenever you write a letter, you just press the macro key to include the letter header.
In a way, macros are like simple programs or batch files. Some applications support sophisticated macros that even allow you to use variables and flow control structures such as loops.
(2) In dBASE programs, a macro is a variable that points to another variable where the data is actually stored. In most other applications, this would be called a link.
batch file Last modified: Monday, September 01, 1997
A file that contains a sequence, or batch, of commands. Batch files are useful for storing sets of commands that are always executed together because you can simply enter the name of the batch file instead of entering each command individually.
In DOS systems, batch files end with a.BAT extension. For example, the following DOS batch file prints the date and time and sets the prompt to GO>:
date
time
prompt [GO>]
Whenever you boot a DOS -based computer, the system automatically executes the batch file named AUTOEXEC.BAT, if it exists.Many operating systems use the terms command file or shell script in place of batch file.
cross-platform Last modified: Sunday, September 01, 1996
Refers to the capability of software or hardware to run identically on different platforms. Many applications for Windows and the Macintosh, for example, now produce binary-compatible files, which means that users can switch from one platform to the other without converting their data to a new format.
Cross-platform computing is becoming increasingly important as local-area networks become better at linking machines of different types.

ISP
Short for Internet Service Provider, a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web and USENET, and send and receive e-mail.
In addition to serving individuals, ISPs also serve large companies, providing a direct connection from the company's networks to the Internet. ISPs themselves are connected to one another through Network Access Points (NAPs).
ISPs are also called IAPs (Internet Access Providers).

proxy server
A server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.
Proxy servers have two main purposes:
Improve Performance: Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as Compuserve and America Online, for example, employ an array of proxy servers.
Filter Requests: Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.
See the Server Types page in the quick reference section of Webopedia for a comparison of server types.

World Wide Web
A system of Internet servers that support specially formatted documents. The documents are formatted in a markup language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web. There are several applications called Web browsers that make it easy to access the World Wide Web; Two of the most popular being Netscape Navigator and Microsoft's Internet Explorer.
World Wide Web is not synonymous with the Internet.

Compatible

(n) Indicates that a product can work with or is equivalent to another, better-known product. The term is often used as a shorthand for IBM-compatible PC , a computer that is compatible with an IBM PC. Another term for a compatible is clone. (adj) The ability of one device or program to work with another device or program. The term compatible implies different degrees of partnership. For example, a printer and a computer are said to be compatible if they can be connected to each other. An IBM compatible PC, on the other hand, is a computer that can run the same software as an IBM PC. Compatibility of two devices, such as printers, usually means that they react to software commands in the same way. Some printers achieve compatibility by tricking the software into believing that the printer is a different machine. This is called emulation. Be aware, however, that hardware compatibility does not always extend to expansion slots. For example, two compatible printers may not accept the same font cartridges. Complete hardware compatibility is denoted by the term plug compatible.Software products are compatible if they use the same data formats. For example, many programs are compatible with dBASE. This means that the files they produce can easily be transformed into a dBASE database or that they can import dBASE files.

API

Abbreviation of application program interface, a set of routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks. A programmer puts the blocks together. Most operating environments, such as MS-Windows, provide an API so that programmers can write applications consistent with the operating environment. Although APIs are designed for programmers, they are ultimately good for users because they guarantee that all programs using a common API will have similar interfaces. This makes it easier for users to learn new programs.

ODBC
(pronounced as separate letters) Short for Open DataBase Connectivity, a standard database access method developed by the SQL Access group in 1992. The goal of ODBC is to make it possible to access any data from any application, regardless of which database management system (DBMS) is handling the data. ODBC manages this by inserting a middle layer, called a database driver , between an application and the DBMS. The purpose of this layer is to translate the application's data queries into commands that the DBMS understands. For this to work, both the application and the DBMS must be ODBC-compliant -- that is, the application must be capable of issuing ODBC commands and the DBMS must be capable of responding to them. Since version 2.0, the standard supports SAG SQL.

servlet
A small program that runs on a server. The term usually refers to a Java applet that runs within a Web server environment. This is analogous to a Java applet that runs within a Web browser environment.
Java servlets are becoming increasingly popular as an alternative to CGI programs. The biggest difference between the two is that a Java applet is persistent. This means that once it is started, it stays in memory and can fulfill multiple requests. In contrast, a CGI program disappears once it has fulfilled a request. The persistence of Java applets makes them faster because there's no wasted time in setting up and tearing down the process.

java
A high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes. Oak was unsuccessful so in 1995 Sun changed the name to Java and modified the language to take advantage of the burgeoning World Wide Web.
Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT).
Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.
database management system Last modified: Wednesday, December 03, 2003
A collection of programs that enables you to store, modify, and extract information from a database. There are many different types of DBMSs, ranging from small systems that run on personal computers to huge systems that run on mainframes. The following are examples of database applications:
computerized library systems
automated teller machines
flight reservation systems
computerized parts inventory systems
From a technical standpoint, DBMSs can differ widely. The terms relational, network, flat, and hierarchical all refer to the way a DBMS organizes information internally. The internal organization can affect how quickly and flexibly you can extract information.
Requests for information from a database are made in the form of a query, which is a stylized question. For example, the query SELECT ALL WHERE NAME = "SMITH" AND AGE > 35
requests all records in which the NAME field is SMITH and the AGE field is greater than 35. The set of rules for constructing queries is known as a query language. Different DBMSs support different query languages, although there is a semi-standardized query language called SQL (structured query language). Sophisticated languages for managing database systems are called fourth-generation languages, or 4GLs for short.
The information from a database can be presented in a variety of formats. Most DBMSs include a report writer program that enables you to output data in the form of a report. Many DBMSs also include a graphics component that enables you to output information in the form of graphs and charts.

SQL

Abbreviation of structured query language, and pronounced either see-kwell or as separate letters. SQL is a standardized query language for requesting information from a database. The original version called SEQUEL (structured English query language) was designed by an IBM research center in 1974 and 1975. SQL was first introduced as a commercial database system in 1979 by Oracle Corporation.
Historically, SQL has been the favorite query language for database management systems running on minicomputers and mainframes. Increasingly, however, SQL is being supported by PC database systems because it supports distributed databases (databases that are spread out over several computer systems). This enables several users on a local-area network to access the same database simultaneously.
Although there are different dialects of SQL, it is nevertheless the closest thing to a standard query language that currently exists. In 1986, ANSI approved a rudimentary version of SQL as the official standard, but most versions of SQL since then have included many extensions to the ANSI standard. In 1991, ANSI updated the standard. The new standard is known as SAG SQL.

database

(1) Often abbreviated DB. A collection of information organized in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system.
Traditional databases are organized by fields, records, and files. A field is a single piece of information; a record is one complete set of fields; and a file is a collection of records. For example, a telephone book is analogous to a file. It contains a list of records, each of which consists of three fields: name, address, and telephone number.
An alternative concept in database design is known as Hypertext. In a Hypertext database, any object, whether it be a piece of text, a picture, or a film, can be linked to any other object. Hypertext databases are particularly useful for organizing large amounts of disparate information, but they are not designed for numerical analysis.
To access information from a database, you need a database management system (DBMS). This is a collection of programs that enables you to enter, organize, and select data in a database.
(2) Increasingly, the term database is used as shorthand for database management system.
CGI Last modified: Tuesday, March 02, 2004
Abbreviation of Common Gateway Interface, a specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The program could be written in any programming language, including C, Perl, Java, or Visual Basic.
CGI programs are the most common way for Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form's data once it's submitted. Another increasingly common way to provide dynamic feedback for Web users is to include scripts or programs that run on the user's machine rather than the Web server. These programs can be Java applets, Java scripts, or ActiveX controls. These technologies are known collectively as client-side solutions, while the use of CGI is a server-side solution because the processing occurs on the Web server.
One problem with CGI is that each time a CGI script is executed, a new process is started. For busy Web sites, this can slow down the server noticeably. A more efficient solution, but one that it is also more difficult to implement, is to use the server's API, such as ISAPI or NSAPI. Another increasingly popular solution is to use Java servlets.

mainframe

A very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simple microprocessor (in watches, for example) at the bottom and moves to supercomputers at the top, mainframes are just below supercomputers. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. But supercomputers can execute a single program faster than a mainframe.

10.2 Pointers and Arrays; Pointer Arithmetic
[This section corresponds to K&R Sec. 5.3]
Pointers do not have to point to single variables. They can also point at the cells of an array. For example, we can write
int *ip;
int a[10];
ip = &a[3];
and we would end up with ip pointing at the fourth cell of the array a (remember, arrays are 0-based, so a[0] is the first cell). We could illustrate the situation like this:


We'd use this ip just like the one in the previous section: *ip gives us what ip points to, which in this case will be the value in a[3].
Once we have a pointer pointing into an array, we can start doing pointer arithmetic. Given that ip is a pointer to a[3], we can add 1 to ip:
ip + 1
What does it mean to add one to a pointer? In C, it gives a pointer to the cell one farther on, which in this case is a[4]. To make this clear, let's assign this new pointer to another pointer variable:
ip2 = ip + 1;
Now the picture looks like this:


If we now do
*ip2 = 4;
we've set a[4] to 4. But it's not necessary to assign a new pointer value to a pointer variable in order to use it; we could also compute a new pointer value and use it immediately:
*(ip + 1) = 5;
In this last example, we've changed a[4] again, setting it to 5. The parentheses are needed because the unary ``contents of'' operator * has higher precedence (i.e., binds more tightly than) the addition operator. If we wrote *ip + 1, without the parentheses, we'd be fetching the value pointed to by ip, and adding 1 to that value. The expression *(ip + 1), on the other hand, accesses the value one past the one pointed to by ip.
Given that we can add 1 to a pointer, it's not surprising that we can add and subtract other numbers as well. If ip still points to a[3], then
*(ip + 3) = 7;
sets a[6] to 7, and
*(ip - 2) = 4;
sets a[1] to 4.
Up above, we added 1 to ip and assigned the new pointer to ip2, but there's no reason we can't add one to a pointer, and change the same pointer:
ip = ip + 1;
Now ip points one past where it used to (to a[4], if we hadn't changed it in the meantime). The shortcuts we learned in a previous chapter all work for pointers, too: we could also increment a pointer using
ip += 1;
or
ip++;
Of course, pointers are not limited to ints. It's quite common to use pointers to other types, especially char. Here is the innards of the mystrcmp function we saw in a previous chapter, rewritten to use pointers. (mystrcmp, you may recall, compares two strings, character by character.)
char *p1 = &str1[0], *p2 = &str2[0];

while(1)
{
if(*p1 != *p2)
return *p1 - *p2;
if(*p1 == '\0' || *p2 == '\0')
return 0;
p1++;
p2++;
}
The autoincrement operator ++ (like its companion, --) makes it easy to do two things at once. We've seen idioms like a[i++] which accesses a[i] and simultaneously increments i, leaving it referencing the next cell of the array a. We can do the same thing with pointers: an expression like *ip++ lets us access what ip points to, while simultaneously incrementing ip so that it points to the next element. The preincrement form works, too: *++ip increments ip, then accesses what it points to. Similarly, we can use notations like *ip-- and *--ip.
As another example, here is the strcpy (string copy) loop from a previous chapter, rewritten to use pointers:
char *dp = &dest[0], *sp = &src[0];
while(*sp != '\0')
*dp++ = *sp++;
*dp = '\0';
(One question that comes up is whether the expression *p++ increments p or what it points to. The answer is that it increments p. To increment what p points to, you can use (*p)++.)
When you're doing pointer arithmetic, you have to remember how big the array the pointer points into is, so that you don't ever point outside it. If the array a has 10 elements, you can't access a[50] or a[-1] or even a[10] (remember, the valid subscripts for a 10-element array run from 0 to 9). Similarly, if a has 10 elements and ip points to a[3], you can't compute or access ip + 10 or ip - 5. (There is one special case: you can, in this case, compute, but not access, a pointer to the nonexistent element just beyond the end of the array, which in this case is &a[10]. This becomes useful when you're doing pointer comparisons, which we'll look at next.)
Using an array name as a pointer
An array name is really a pointer to the first element of the array. For example, the following is legal.
int b[100]; // b is an array of 100 ints.
int* p; // p is a pointer to an int.
p = b; // Assigns the address of first element of b to p.
p = &b[0]; // Exactly the same assignment as above.
Array name is a const pointer
When you declare an array, the name is a pointer, which cannot be altered. In the previous example, you could never make this assignment.
p = b; // Legal -- p is not a constant.
b = p; // ILLEGAL because b is a constant, altho the correct type.
Pointer arithmetic
"Meaningful" arithmetic operations are allowed on pointers.
· Add or subtract integers to/from a pointer. The result is a pointer. Subtract two pointers to the same type. The result is an int. Multiplying, adding two pointers, etc. don't make sense.
Pointer addition and element size
When you add an integer to a pointer, the integer is multiplied by the element size of the type that the pointer points to.
// Assume sizeof(int) is 4.
int b[100]; // b is an array of 100 ints.
int* p; // p is a a pointer to an int.
p = b; // Assigns address of first element of b. Ie, &b[0]
p = p + 1; // Adds 4 to p (4 == 1 * sizeof(int)). Ie, &b[1]



Fifth Normal Form (5NF)

The normal forms discussed so far required that the given relation R if not in the given normal form be decomposed in two relations to meet the requirements of the normal form. In some rare cases, a relation can have problems like redundant information and update anomalies because of it but cannot be decomposed in two relations to remove the problems. In such cases it may be possible to decompose the relation in three or more relations using the 5NF.
The fifth normal form deals with join-dependencies which is a generalisation of the MVD. The aim of fifth normal form is to have relations that cannot be decomposed further. A relation in 5NF cannot be constructed from several smaller relations.
A relation R satisfies join dependency (R1, R2, ..., Rn) if and only if R is equal to the join of
R1, R2, ..., Rn where Ri are subsets of the set of attributes of R.
A relation R is in 5NF (or project-join normal form, PJNF) if for all join dependencies at least one of the following holds.
(a) (R1, R2, ..., Rn) is a trivial join-dependency (that is, one of Ri is R)
(b) Every Ri is a candidate key for R.
An example of 5NF can be provided by the example below that deals with departments, subjects and students.

dept subject student
Comp. Sc.
Mathematics
Comp. Sc.
Comp. Sc.
Physics
Chemistry CP1000
MA1000
CP2000
CP3000
PH1000
CH2000 John Smith
John Smith
Arun Kumar
Reena Rani
Raymond Chew
Albert Garcia
The above relation says that Comp. Sc. offers subjects CP1000, CP2000 and CP3000 which are taken by a variety of students. No student takes all the subjects and no subject has all students enrolled in it and therefore all three fields are needed to represent the information.
The above relation does not show MVDs since the attributes subject and student are not independent; they are related to each other and the pairings have significant information in them. The relation can therefore not be decomposed in two relations
(dept, subject), and
(dept, student)
without loosing some important information. The relation can however be decomposed in the following three relations
(dept, subject), and
(dept, student)
(subject, student)
and now it can be shown that this decomposition is lossless.
Multivalued Normalisation -Fourth Normal Form
We have considered an example of Programmer(Emp name, qualification, languages) and discussed the problems that may arise if the relation is not normalised further. We also saw how the relation could be decomposed into P1(Emp name, qualifications) and P2(Emp name, languages) to overcome these problems. The decomposed relations are in fourth normal form (4NF) which we shall now define.
We are now ready to define 4NF. A relation R is in 4NF if, whenever a multivalued dependency
X -> Y holds then either
(a) the dependency is trivial, or
(b) X is a candidate key for R.
As noted earlier, the dependency X ->> ø or X ->> Y in a relation R (X, Y) is trivial since they must hold for all R (X, Y). Similarly (X, Y) -> Z must hold for all relations R (X, Y, Z) with only three attributes.
In fourth normal form, we have a relation that has information about only one entity. If a relation has more than one multivalue attribute, we should decompose it to remove difficulties with multivalued facts.
Intuitively R is in 4NF if all dependencies are a result of keys. When multivalued dependencies exist, a relation should not contain two or more independent multivalued attributes. The decomposition of a relation to achieve 4NF would normally result in not only reduction of redundancies but also avoidance of anomalies.
Single-Valued Dependencies
Initially Codd (1972) presented three normal forms (1NF, 2NF and 3NF) all based on functional dependencies among the attributes of a relation. Later Boyce and Codd proposed another normal form called the Boyce-Codd normal form (BCNF). The fourth and fifth normal forms are based on multivalue and join dependencies and were proposed later.
The primary objective of normalization is to avoid some of the anomalies that we discussed at the beginning of the chapter.
Example Normalisation
Un-Normalised Data

ORDER DETAILS 1
WID-008
Green Widget
Data is presented in a single column. In tis caste the following data is contained:
Quantity, Item ID and item Description. Since multiple unrelated values are stored in a column, this data is considered un-normalised.
First normal Form

ORDER DETAILS ItemCode Description Quantity
WID-008 Green Widget 1
Data is now in First Normal Form (1NF). Data items have been put in their own columns, and the columns furnished with a description. For data to be in 1NF each piece of information should be in its own column,and each row of data should contain the same columns.
Second Normal Form

ORDER DETAILS OrderID ItemCode Description Quantity
2345 WID-008 Green Widget 1
Data is now in Second Normal Form (2NF). 2NF is based on 1NF, with the addition that a unique identifier is added to each row - In this case the OrderID value. In most cases this unique value is a counter, rather than being related to the data. Each non-key attribute should be functionally dependent on the primary key for the table.
Third Normal Form

ORDER DETAILS OrderID ItemCode Quantity
2345 WID-008 1

ITEM DETAILS ItemCode Description
WID-008 Green Widget
Data is now in Third Normal Form (3NF). All attributes not dependent on the primary key should be moved to a separate table. Repetition of data is also eliminated. In this case, the tables are linked by the ItemCode attribute.
First Normal Form (1NF)
A table satisfying the properties of a relation is said to be in first normal form. As discussed in an earlier chapter, a relation cannot have multivalued or composite attributes. This is what the 1NF requires.
A relation is in 1NF if and only if all underlying domains contain atomic values only.
The first normal form deals only with the basic structure of the relation and does not resolve the problems of redundant information or the anomalies discussed earlier. All relations discussed in these notes are in 1NF.
For example consider the following example relation:
student (sno, sname, dob)
Add some other attributes so it has anomalies and is not in 2NF
The attribute dob is the date of birth and the primary key of the relation is sno with the functional dependencies sno -> sname and sno -> dob. The relation is in 1NF as long as dob is considered an atomic value and not consisting of three components (day, month, year). The above relation of course suffers from all the anomalies that we have discussed earlier and needs to be normalized. (add example with date of birth)
Second Normal Form (2NF)
The second normal form attempts to deal with the problems that are identified with the relation above that is in 1NF. The aim of second normal form is to ensure that all information in one relation is only about one thing.
A relation is in 2NF if it is in 1NF and every non-key attribute is fully dependent on each candidate key of the relation.
To understand the above definition of 2NF we need to define the concept of key attributes. Each attribute of a relation that participates in at least one candidate key of is a key attribute of the relation. All other attributes are called non-key.
The concept of 2NF requires that all attributes that are not part of a candidate key be fully dependent on each candidate key. If we consider the relation
student (sno, sname, cno, cname)
and the functional dependencies
sno -> sname
cno -> cname
and assume that (sno, cno) is the only candidate key (and therefore the primary key), the relation is not in 2NF since sname and cname are not fully dependent on the key. The above relation suffers from the same anomalies and repetition of information as discussed above since sname and cname will be repeated. To resolve these difficulties we could remove those attributes from the relation that are not fully dependent on the candidate keys of the relations. Therefore we decompose the relation into the following projections of the original relation:
S1 (sno, sname)
S2 (cno, cname)
SC (sno, cno)
Use an example that leaves one relation in 2NF but not in 3NF.
We may recover the original relation by taking the natural join of the three relations.
If however we assume that sname and cname are unique and therefore we have the following candidate keys
(sno, cno)
(sno, cname)
(sname, cno)
(sname, cname)
The above relation is now in 2NF since the relation has no non-key attributes. The relation still has the same problems as before but it then does satisfy the requirements of 2NF. Higher level normalization is needed to resolve such problems with relations that are in 2NF and further normalization will result in decomposition of such relations.
Third Normal Form (3NF)
Although transforming a relation that is not in 2NF into a number of relations that are in 2NF removes many of the anomalies that appear in the relation that was not in 2NF, not all anomalies are removed and further normalization is sometime needed to ensure further removal of anomalies. These anomalies arise because a 2NF relation may have attributes that are not directly related to the thing that is being described by the candidate keys of the relation. Let us first define the 3NF.
A relation R is in third normal form if it is in 2NF and every non-key attribute of R is non-transitively dependent on each candidate key of R.
To understand the third normal form, we need to define transitive dependence which is based on one of Armstrong's axioms. Let A, B and C be three attributes of a relation R such that A -> B and B -> C. From these FDs, we may derive A -> C. As noted earlier, this dependence A -> C is transitive.
The 3NF differs from the 2NF in that all non-key attributes in 3NF are required to be directly dependent on each candidate key of the relation. The 3NF therefore insists, in the words of Kent (1983) that all facts in the relation are about the key (or the thing that the key identifies), the whole key and nothing but the key. If some attributes are dependent on the keys transitively then that is an indication that those attributes provide information not about the key but about a kno-key attribute. So the information is not directly about the key, although it obviously is related to the key.
Consider the following relation
subject (cno, cname, instructor, office)
Assume that cname is not unique and therefore cno is the only candidate key. The following functional dependencies exist
cno -> cname
cno -> instructor
instructor -> office
We can derive cno -> office from the above functional dependencies and therefore the above relation is in 2NF. The relation is however not in 3NF since office is not directly dependent on cno. This transitive dependence is an indication that the relation has information about more than one thing (viz. course and instructor) and should therefore be decomposed. The primary difficulty with the above relation is that an instructor might be responsible for several subjects and therefore his office address may need to be repeated many times. This leads to all the problems that we identified at the beginning of this chapter. To overcome these difficulties we need to decompose the above relation in the following two relations:
s (cno, cname, instructor)
ins (instructor, office)
s is now in 3NF and so is ins.
An alternate decomposition of the relation subject is possible:
s(cno, cname)
inst(instructor, office)
si(cno, instructor)
The decomposition into three relations is not necessary since the original relation is based on the assumption of one instructor for each course.
The 3NF is usually quite adequate for most relational database designs. There are however some situations, for example the relation student(sno, sname, cno, cname) discussed in 2NF above, where 3NF may not eliminate all the redundancies and inconsistencies. The problem with the relation student(sno, sname, cno, cname) is because of the redundant information in the candidate keys. These are resolved by further normalization using the BCNF.