Tech tut

C (Not SHE) ki PATHSHALA
(SUSWAGATAM)
Sabhi ko mera yane Ketan urf Nano
ka Pyar Bhara Namshkar
Ap aye hum khush ho gaye

In Points pe Gaur Kijiye
• We r here for Discussing C programming
Fundas…so that u will rock ur campus
placements

• I will discuss some points with you. Yeh koi
routine class nahi hai…I feel u will enjoy these
sessions..as Mera moto hai classes fun honi
chahiye….

What u expect from me and answers
• If you expect that u will be a champ after
attending these sessions then u ve wrong
impression…mai bhagwan nahi hun ki joh apki
c chand dino me acchi kar dunga….

• If u ask kya mere sessions boring( boys ki
bhasha me c se start hone wala word) hoge toh
my answers is at some points can be boring but
overall they will be fun

What I expect from you and answers
• U will keep ur Cell phones in Silent modes….
• If u r seating near ur bf(for girls I guess :P),ff(for
both boys and girls) and gf ( again for boys I
guess :P) make sure u do not chit chat with
them as it disturbs me and itz really annoying

• You will get plenty of time for discussions,
games and masti for making noise

• Pz do not be shy in asking me any
difficulty…for personally asking ur difficulty
write ur problem on any blank page…rt ur
name and email id…or I will rt to you ur
answer the next day…

• OR SIMPLY RAISE UR HAND AND ASK….

Bhaiyo & Behno PZ NOTE IT…..
• If you want be a real gud programmer in C do
following things :-
A] Always make a flowchart before writing the
program..HUM SAB PRACTICALS ME PAHILE
PROGRAM TAPTE HAI…THEN WE MAKE
FLOWCHART…REALLY BAD PRACTISE….

B]Make Memory Blocks on paper for any kind of
variables or operations…apki adhi se jayda
difficulties yehi solve ho jayegi…C LANG is all
abt Memory Management

C]Practice makes the MAN as well as the
WOMEN perfect…so do it as much as you can…

D]AB what u need to crack campus questions is
Develop understanding of basic things in C and
develop the skill of debugging a program

E]They try to test ur debugging skills by asking
yourself simple questions on basic
concepts…like for eg rules for integer
declaration…

My way…..
• My way is Simple…I will mostly try to cover
THEORY concepts with the help of problems
…which will help you to crack the questions

• The questions have been compiled and tested
and have been directly taken from campus
placement tests of MNCs…which will basically
show you how they ask…and What they ask…

• I need ur support so that u shud read material
like any gud c book of kanitker sir alongside
my sessions after going home…so that it will
help you…

• I can not teach you everything in detail as I do
not have time…you will see that at the end of
the course u will know what kind of questions
are asked and what shud be ur attitude and
approach towards solving them and what data
is required to solve them

Topics which we will do…
1]Types, Operators and Expressions

2]Control Flow

3]Functions and Program Structure

4]Pointers and Arrays

5]Structures

6]Input and Output

1.Types , Operators, Expressions
Variables & Constants :-

Def :- They are the basic data objects manipulated
in program…

Ab dekhte hai variables ke bare me info joh apko
pata hona chahiye for Questions….

• You will be asked questions on variable naming
rules….Typical rules on which questions are
asked are :-

What will be output of the following c program?
#include<stdio.h>
int main()
{
int _=5;
int __=10;
int ___;
___=_+__;
printf("%i",___);
return 0;
}

A]5 B]10 C]15 D]Compilation Error E]None of these

• ANS – C]15…..
Reason :- Important rule for variable naming
says that the first character in the name must
be a letter…But “_” underscore is counted as a
letter….Yeh Trick thi wahan pe….

So ap Dekh sakte hai…question was not
difficult…bas yeh simple rule yad rakhiye…

#include<stdio.h>
int main()
{
int goto=5;
printf("%d",goto);
return 0;
}

A]5 B]* C]** D]Compilation Error E]None of these

• ANS – D] Compilation Error
Reason :- We have used the word “goto” as the
name for the variable and assigned it the value
5…But “goto” is a keyword in C which already
has a predefined function…..so Rule kehta
hai…Ki Variable Name must not contain
Keyword..Note this rule…Ispe Kafi bar sawal Ata
hai…

To tackle this…Just go thru the list of keywords in
C..


#include<stdio.h>
int main(){
long int 1a=5l;
printf("%ld",1a);
return 0;
}


• ANS :- D]Compilation Error
Reason :- Variable name must start with a Letter
… But we have declared ‘1a’ and the first
character in this name is a number…which is a
wrong practice…

Correct Rule is the first character in variable
name must be a Letter….

Now , This is a very Special and Tricky question..

#include<stdio.h>
int main()
{
int class=150;
int public=25;
int private=30;
class = class/( private – public);
printf("%d",class);
return 0;
}
A]30 B] 2 C]Compilation Error D]None of these

• ANS :- A] 30…
Reason :- Now Why 30?????
You see Class , Public, Private….Yeh 3 joh hai yeh
tin tighda kam bighda nahi hai…balki C++ ke
keywords hai…

So the Point to note is…Even if you can not use
the “KEYWORDS OF C” as variable names but
YOU CAN USE THE KEYWORDS OF C++ AS
VARIABLE NAMES…PLEASE NOTE DOWN THIS
POINT….


#include<stdio.h>
int xyz=10;
int main()
{
int xyz=20;
printf("%d",xyz);
return 0;
}


• ANS :- B]20
Reason :- ????
You will observe that we gave the same name to
both the variables…But Differences aisa hai
ki…Ek Variable main ke ander hai…and ek main
ke bahar…so Scope of that variable inside the
main remains for that main…that is it can be
manipulated inside the main…
SO IMP RULE :- TWO VARIABLES CAN HAVE SAME
NAME BUT IN DIFFRERENT SCOPES…

NOW SEE THE VARIATION IN THE NEXT
QUESTION…..

#include<stdio.h>
int main()
{
int xyz=20;
{
int xyz=40;
}
printf("%d",xyz);
return 0;
}

A]20 B]40 C]0 D] Compilation Error E]None of these

• ANS – A]20
Reason :- Observe the braces…The scope of
variable xyz =40 is limited to the braces in
which it is declared..But the printf statement is
written in the main and not in the braces…and
the declaration xyz=20 is in main…so the printf
will print as 20….

AGAIN IMP RULE IS…. TWO VARIABLES CAN
HAVE SAME NAME BUT IN DIFFRERENT
SCOPES…


#include<stdio.h>
int main()
{
int main = 80;
printf("%d",main);
return 0;
}
A] 80 B]0 C]Garbage Value D]Compilation Error
E]None of these

• ANS :- A]80
Reason :- Yahan pe note the point ki we can
declare the variable name as main….C ko koi
issues nahi hai is bare me….


#include<stdio.h>
int main()
{
int ABC=10;
printf("%d",abc);
return 0;
}

• ANS :- D] Compilation Error
Reason :- Variable names are character sensitive
and so abc and ABC are different…

Data Types
There r few data types in C viz :-
1] char :- a single byte, capable of holding one
character in the local character set
for eg. Char kp =‘A’;

2] int :- an integer, typically reflecting the natural
size of integers on the host machine
for eg int kp =81;

3]float :- single-precision floating point
(For this please check IEEE 754 2008
format.)
for eg float kp=0.23;
4] double :- double-precision floating point
(For this please check IEEE 754 2008
format.)
for eg double kp =0.23;

Qualifiers
• Integers can be applied two qualifiers viz short
and long.For eg.
short int sh;
long int counter;
The word int can be omitted in such declarations…

• The qualifier signed and unsigned may be
applied to char or any integer….

• Unsigned numbers are always positive or zero
• Obey Law of Arithmetic modulo 2n

• Where n is number of bits in the type
• So if chars are 8 bits unsigned char variables
have values between 0 and 255, while signed
chars have values between -128 and 127
• Whether plain chars are unsigned or signed is
machine dependent

What abt the sizes?
• For the sizes of Data Types each compiler is free
to choose appropriate sizes for its own hardware

• But the **Conditions Applied are :-
A]Shorts and Ints are at least 16 bits
B]Longs are at least 32 bits
C]Long > Int > Short

• The type long double specifies extended-
precision floating point.

• float, double and long double could represent
one, two or three distinct sizes

• The standard headers <limits.h> and <float.h>
contain symbolic constants for all of these sizes,
along with other properties of the machine and
compiler.

Constants
• There are 5 types of Constants viz :-
1] Integer Constant :- for eg 1234 is int constant
1234l or 1234L is Long Int Constant
1234ul or 1234 UL indicates unsigned Long
1234u or 1234 U indicates unsigned int
2]Floating Point Constants :- They Contain a
decimal point for eg 123.4 or 1e -2.Type is
double unless suffixed… 123.4 is Double
Constant
123.4f or 123.4F is floating Constant
123.4l or 123.4L is Long Double Constant

3] Character Constant :- A character constant is an
integer, written as one character within single
quotes, such as ‘0’.The value of this is 48
according to the ASCII table and not numeric 0
as we have attached single quotes….

4]String Constant :- A string constant, or string
literal, is a sequence of zero or more characters
surrounded by double quotes, as in
"I am a string"

• 5]Enumeration Constant :- An enumeration is a
list of constant integer values, as in
enum boolean { NO, YES };
Specialty of this enum is by default the value of
no wud be 0 and yes wud be 1.Boolean the
name of the enum. The user can also specify
the value of the constants inside. If not given
then only default values are given as 0 1 2 and
so on….
For eg. enum escapes { BELL = 'a', BACKSPACE =
'b', TAB = 't',NEWLINE = 'n', VTAB = 'v',
RETURN = 'r' };

What will be output when you will execute
following c code?

#include<stdio.h>
void main(){
printf("%dt",sizeof(6.5));
printf("%dt",sizeof(90000));
printf("%d",sizeof('A'));
}
There can not be a specific answer to this
question…Why????

ANS :- As we saw the values of sizes depend on
the compiler choosing appropriate sizes for the
hardware…there can not be a specific answer to
this question….

This is an information question to you…Please note
the answer…
Consider on following declaring of enum.
(i) enum cricket {Gambhir,Smith,Sehwag}c;
(ii) enum cricket {Gambhir,Smith,Sehwag};
(iii) enum {Gambhir,Smith=-5,Sehwag}c;
(iv) enum c {Gambhir,Smith,Sehwag};

Which one of the above is Correct Declaration?

ANS :- ALL ARE CORRECT….

Syntax of enum data type is:
enum [<tag_name>]{
<enum_constanat_name> [=<integer_ value>],
…
} [<var_name>,…]

Note:
[] : Represents optional .
<>: Represents any valid c identifier

• This question is combined of operator and type casting that
happens in C :-
What will be output when you will execute following c code?

#include<stdio.h>
void main(){
signed x;
unsigned y;
x = 10 +- 10u + 10u +- 10;
y = x;
if(x==y)
printf("%d %d",x,y);
else if(x!=y)
printf("%u %u",x,y);
}
A] 0 0 B] 65536 -10 C] 0 65536 D]65536 0

ANS :- A] 0 0… WHY???
Reason :-
x = 10 +- 10u + 10u +- 10;
10: It is signed integer constant.
10u: It is unsigned integer constant.
x :signed integer variable….
Lower data type operand always automatically
type casted into the operand of higher data type
before performing the operation and result will
be higher data type

a +- b

a +(THIS IS FOR EXPRESSION) –(this gets attached
as a sign of no)b

a + (-b)
This is Calculated….

Signed is higher data type than unsigned int.
So, Corresponding signed value of unsigned 10u
Is +10
And As we know operators enjoy higher
precedence than binary operators. So our
expression is:
x = 10 + (-10u) + 10u + (-10);
= 10 + -10 + 10 + (-10);
=0
y = x =0


#include<stdio.h>
const enum Alpha{
X,
Y=5,
Z
}p=10;
void main(){
enum Alpha a,b;
a= X;
b= Z;
printf("%d",a+b-p);
}
A] -4 B]-5 C]11 D] 10 E]Error :- Can not modify object

ANS – A]-4
Reason :- Default value of enum constant X is zero
and
Z=Y+1=5+1=6
So, a + b – p = 0 + 6 -10 = -4

Operators
• The important operators for questions are
Increment and Decrement operators, Unary
operators and Logical Operators…

• Another thing that must be taken into account
is precedence of operators…

Increment and Decrement Operator
• The increment operator ++ adds 1 to its
operand, while the decrement operator --
subtracts 1.
• But the confusing and interesting part is they
can be used prefix or post fix …

• For example
If n is 5
Then x = n++ will give x to be 5…as n is postfix
and is calculated after the expression…

• But if n is 5
And x = ++n
Then x is 6…as now ++ is pre increment and n is
incremented before expression is calculated…

+ and – in unary form are the important operators
in example like 10 + -(10u)
Here precedence is given to -10u and –ve sign is
the unary operator and + is binary operator…

• Logical operators are :-
Logical and :- &&
Logical or :- ||

These should not be confused with bitwise
operators & (bitwise and) and |(bitwise or)

What will be output of the following program?

#include<stdio.h>
int main(){
int i=1;
i=2+2*i++;
printf("%d",i);
return 0;
}

• ANS :- 5

Reason :- i++ is a postfix operator…so the
expression i = 2 + 2 *1 will be evaluated… i = 4
and then i++ will be evaluated so it will be i =5
and i will be printed as 5…


#include<stdio.h>
int main(){
int a=2,b=7,c=10;
c=a==b;
printf("%d",c);
return 0;
}

ANS :- 0 KYUN?????
Go Back To the operator precedence table and you
will see the expression a==b will be evaluated
first….a = 2 and b = 7…so a is not equal to b and
so the condition a==b is false and the value of
the expression is 0 as the condition is false…now
therefore c = 0…also observe c is declared as int
and thus c= 10 will not matter and a new value
will be assigned to c....

Now my questions is….if it was const c i.e.
constant c in place of int c...

#include<stdio.h>
void main()
{
int x;
x=10,20,30;
printf("%d",x);
return 0;
}

ANS :- 10
Reason :- Since assignment operator (=) has more
precedence than comma operator .So =
operator will be evaluated first than comma
operator. In the following expression

x = 10, 20, 30

First 10 will be assigned to x then comma
operator will be evaluated.


#include<stdio.h>
int main(){
int a;
a=015 + 0x71 +5;
printf("%d",a);
return 0;
}

ANS :- 131….Kaise????
Reason :- Here we introduce type casting…u will
observe the variable a is int…so 015 is octal
number its decimal equivalent is = 5 * 8 ^ 0 + 1 *
8 ^ 1 = 5 + 8 = 13 0x71 is hexadecimal number
(0x is symbol of hexadecimal) its decimal
equivalent is = 1 * 16 ^ 0 + 7 * 16 ^ 1 = 1 + 112 =
113
So, a = 13 + 113 + 5 = 131

Control Flow
IF – Else

if (expression)
statement1
else
Statement2

else part of an if-else is optional

Common Mistake :- Use Proper Braces….Nested If
if (n > 0) if(n>0)
{ if(a>b)
if (a > b) {
z = a; z=a;
} }
else else
{ {
z = b; z=b;
} }

Another Common Mistake is Use of Symbol =
instead of == during comparison for eg

If(a=b) instead of if(a==b)

a=b assigns value of b to a

Where a==b properly compares the value of a
with b

Else If
if (expression)
statement
else if (expression)
statement
statement
statement
else
statement

expressions are evaluated in order

if an expression is true, the statement associated
with it is executed, and this terminates the
whole chain.

else
statement
can be omitted, or it may be used for error
checking to catch an ``impossible'' condition.

Switch :-
The switch statement is a multi-way decision that
tests whether an expression matches one of
a number of constant integer values, and branches
accordingly.

switch (expression) {
case const-expr: statements
case const-expr: statements
default: statements
}

All case expressions must be different. The case
labeled default is executed if none of the other
cases are satisfied. A default is optional; if it isn't
there and if none of the cases match, no action at
all takes place. Cases and the default clause can
occur in any order.

Break Statement…
switch (expression) {
case const-expr: statements break;
case const-expr: statements break;
default: statements
}
• By break it will leave the switch…otherwise if
there is no brake statement it will go on falling
and executing next cases….
• We can type return also instead of break…

What will be output when you will execute following c
code?

#include<stdio.h>
void main()
{
int a=100;
if(a>10)
printf("M.S. Dhoni");
else if(a>20)
printf("M.E.K Hussey");
else if(a>30)
printf("A.B. de villiers");
}

A] M.S.Dhoni B] M.E.K. Hussey C]A.B.de villiers

ANS :- A]M.S.Dhoni
Yenna Rascala Mind it well ……
Reason :-
In case of if – if else – if else … Statement if first if
clause is true the compiler will never check rest of
the if else clause and so on.

Please Note Down…..

following c code?
#include<stdio.h>
void main(){
int x=-1,y=-1;
if(++x=++y)
printf("R.T. Ponting");
else
printf("C.H. Gayle");
}
A] R.T.Pointing B]C.H.Gayle C]Compilation Error

ANS :- C] Compilation Error …WHY ?????
Consider following statement:
++x=++y
As we know ++ is pre increment operator in the
above statement. This operator increments the
value of any integral variable by one and return
that value. After performing pre increments
above statement will be:
0=0
In C language it is illegal to assign a constant value
to another constant.

following c code?
#include<stdio.h>
void main(){
int m=5,n=10,q=20;
if(q/n*m)
printf("William Gates");
else
printf(" Warren Buffet");
printf(" Carlos Slim Helu");
}
A]William Gates B]William Gates Carlos Slim Helu

ANS :- B] William Gates Carlos Slim Helu
Reason :-
Consider the following expression:
q/n*m

In this expression there are two operators. They
are: /: Division operator
*: Multiplication operator
Precedence and associate of each operator is as
follow:

PRECEDENCE OPERATOR ASSOCIATE
1 /,* Left to Right

Precedence of both operators is same. Hence associate will decide
which operator will execute first. Since Associate is left to right. So
/ operator will execute then * operator will execute.
=q/n*m
= 20 / 10 * 5
=2*5
=10

As we know in c zero represents false and any non-zero number
represents true. Since 10 is non- zero number so if clause will
execute and print: William Gates

Since in else clause there is not any opening and
closing curly bracket. So compiler will treat only
one statement as a else part. Hence last
statement i.e. printf(" Carlos Slim Helu");is not
part of if-else statement. So at the end compiler
will also print: Carlos Slim Helu So output of
above code will be: William Gates Carlos Slim
Helu

code?
#include<stdio.h>
void main(){
if("ABC") printf("Barack Obaman");
if(-1) printf("Hu Jintaon");
if(.92L) printf("Nicolas Sarkozyn");
if(0) printf("Ben Bernanken");
if('W') printf("Vladimir Putinn");
}

ANS :- Barack Obama
Hu Jintao
Nicolas Sarkozy
Vladimir Putin

Reason :- “ABC”: It is string constant and it will always return a
non-zero memory address.0.92L: It is long double constant.
‘W’: It is character constant and it has ASCII Value which is non
zero Number

As we know in c language zero represents false and any non-zero
number represents true. In this program condition of first,
second, third and fifth if statements are true.

following c code?
#include<stdio.h>
void main(){
int a=5,b=10;
if(++a||++b)
printf("%d %d",a,b);
else
printf("John Terry");
}

ANS :- 6 10
Reason :-
++a || ++b

In this expression || is Logical OR operator. Two
important properties of this operator are:
Property 1:
(Expression1) || (Expression2)
|| operator returns 0 if and only if both expressions
return a zero otherwise it || operator returns 1.

Property 2:

To optimize the execution time there is rule,
Expression2 will only evaluate if and only if
Expression1 return zero.

In this program initial value of a is 5. So ++a will be 6.
Since ++a is returning a non-zero so ++b will not
execute and if condition will be true and if clause will
be executed.


#include<stdio.h>
void main(){
int x=1;
if(x--)
printf("The Godfather");
--x;
else
printf("%d",x);
}

ANS :- Compilation ERROR….
Reason :- If you are not using { and } in if clause
then you can write only one statement.

following c code?
#include<stdio.h>
void main(){
int a=2;
if(a--,--a,a)
printf("The Dalai Lama");
else
printf("Jim Rogers");
}
A]The Dalai Lama B]Jim Rogers C] Compile Error

ANS :- B] Jim Rogers
Reason :-
a-- , --a , a

In c comma is behaves as separator as well as
operator. In the above expression comma is behaving
as operator. Comma operator enjoy lest precedence in
precedence table and its associatively is left to right. So
first of all left most comma operator will perform
operation then right most comma will operator in the
above expression.

After performing a-- : a will be 2
After performing --a : a will be 0
a=0

As we know in c zero represents false and any non-
zero number represents true. Hence else part will
execute.

What will be output when you will execute following
c code?
#include<stdio.h>
void main(){
int check=2;
switch(check){
case 1: printf("D.W.Steyn");
case 2: printf(" M.G.Johnson");
case 3: printf(" Mohammad Asif");
default: printf(" M.Muralidaran");
}
}

ANS :- M.G.Johnson Mohammad Asif
M.Muralidaran

If we will not use break keyword in each case the
program control will come in each case after the
case witch satisfy the switch condition.

#include<stdio.h>
enum actor{
SeanPenn=5,
AlPacino= -2,
GaryOldman,
EdNorton
};
void main(){
enum actor a=0;
switch(a){
case SeanPenn: printf("Kevin Spacey");
break;
case AlPacino: printf("Paul Giamatti");
break;
case GaryOldman:printf("Donald Shuterland");
break;
case EdNorton: printf("Johnny Depp");
}
}

ANS :- Johny Depp …WHY????
Reason :- Default value of enum constant
GaryOldman = -2 +1 = -1
And default value of enum constant
EdNorton = -1 + 1 = 0
Note: Case expression can be enum constant.

What will be output when you will execute following code?
#include<stdio.h>
void main(){
switch(6){
case 6.0f:printf("Salma Hayek");
break;
case 6.0: printf(“Katrina Kaif");
break;
case 6.0L:printf(“Gerard Butler");
break;
default: printf(“Jonathan Rhys Meyers");
}
}
A]Salma Hayek B]Katrina Kaif C]Gerard Butler D] Jonathan
Rhys Meyers E]Compilation Error

ANS :- E]Compilation Error
Reason :-
Case expression must be integral constant
expression. If it is not integer then it is
automatically type casted into integer value.

so. (int)6.0f = 6
(int)6.0 = 6
(int)6.0L = 6
In c duplicate case is not possible.

code?
#include<stdio.h>
void main(){
switch(5/2*6+3.0){
case 3:printf("David Beckham");
break;
case 15:printf("Ronaldinho");
break;
case 0:printf("Lionel Messi");
break;
default:printf("Ronaldo");
}
}
A]David Beckham B] Ronaldinho C] Lionel Messi D] Ronaldo
E]Compilation Error

ANS :- E]Compilation Error
Reason :- Consider on the expression:

5/2*6+3.0
=2*6+3.0
=12 + 3.0
=15.0
In c switch expression must return an integer
value. It cannot be float, double or long double


#include<stdio.h>
void main(){
int a=5;
a=a>=4;
switch(2){
case 0:int a=8;
case 1:int a=10;
case 2:++a;
case 3:printf("%d",a);
}
}
A] 2 B] Compilation error C] 11

ANS :- B] Compilation Error
Reason :- We can not declare any variable in any
case of switch case statement.

Suppose Now I remove the int part behind int a
= 10 and int a =8 ….Now what will be the
o/p????

Loops
While and For
While Loop :-

while (expression)
Statement

The expression is evaluated. If it is non-zero,
statement is executed and expression is reevaluated.
This cycle continues until expression becomes zero,
at which point execution resumes after statement.

For Loop :-
The for statement
for (expr1; expr2; expr3)
Statement

Grammatically, the three components of a for loop are expressions.
Most commonly, expr1 and expr3 are assignments or function calls and
expr2 is a relational expression. Any of the three parts can be omitted,
although the semicolons must remain. If expr1 or expr3 is omitted, it
is simply dropped from the expansion. If the test, expr2, is not present,
it is taken as permanently true, so
for ( ; ; ) {
...
}
is an ``infinite'' loop, presumably to be broken by other means, such as
a break or return.

Do while Loop
The syntax of the do is
do
statement
while (expression);

The statement is executed, then expression is
evaluated. If it is true, statement is evaluated
again, and so on. When the expression becomes
false, the loop terminates.

Break and Continue
Break:-

The break statement provides an early exit from
for, while, and do, just as from switch. A break
causes the innermost enclosing loop or switch to
be exited immediately.

Continue :-
The continue statement is related to break, but
less often used; it causes the next iteration of
the enclosing for, while, or do loop to begin.

for (i = 0; i < n; i++)
if (a[i] < 0) /* skip negative elements */
continue;

Basically used in nesting of loops

Go To and Labels

C provides the infinitely-abusable goto statement,
and labels to branch to. Formally, the goto
statement is never necessary, and in practice it is
almost always easy to write code without it.

Nevertheless, there are a few situations where gotos may find a place.
The most common is to abandon processing in some deeply nested
structure, such as breaking out of two or more loops at once. The break
statement cannot be used directly since it only exits from the
innermost loop. Thus:

for ( ... )
I Love You;
for ( ... ) {
...
if (disaster)
goto error;
}
...
error:
/* clean up the mess */

With a few exceptions like those cited here, code
that relies on goto statements is generally
harder to understand and to maintain than code
without gotos.

So it must be rarely used…The Consiquences can
be disastrous….

What will be output of following c code?
#include<stdio.h>
extern int x;
int main(){
do{
do{
printf("%o",x);
}
while(!-2);
}
while(0);
return 0;
}
int x=8;

ANS :- 10
Reason :- Here variable x is extern type. So it will search
the definition of variable x. which is present at the end of
the code. So value of variable x =8
There are two do-while loops in the above code. AS we
know do-while executes at least one time even that
condition is false. So program control will reach at printf
statement at it will print octal number 10 which is equal to
decimal number 8.
Note: %o is used to print the number in octal format.
In inner do- while loop while condition is ! -2 = 0
In C zero means false. Hence program control will come
out of the inner do-while loop. In outer do-while loop
while condition is 0. That is again false. So program control
will also come out of the outer do-while loop.

#include<stdio.h>
int main(){
int i=2,j=2;
while(i+1?--i:j++)
printf("%d",i);
return 0;
}
HINT :- Condition ? (if true executes this) : (if false
executes this)
? :- ternary operator

ANS :- 1
Reason :- Consider the while loop condition: i + 1 ? -- i :++j
In first iteration: i + 1 = 3 (True)
So ternary operator will return --i i.e. 1
In c 1 means true so while condition is true. Hence printf
statement will print 1
In second iteration:
i+ 1 = 2 (True)
So ternary operator will return -–i i.e. 0
In c zero means false so while condition is false. Hence
program control will come out of the while loop.


#include<stdio.h>
int main(){
int x=011,i;
for(i=0;i<x;i+=3){
printf("Start ");
continue;
printf("End");
}
return 0;
}

ANS :- Start Start Start
Reason :- 011 is octal number. Its equivalent
decimal value is 9.
So, x = 9

First iteration:
i=0
i < x i.e. 0 < 9 i.e. if loop condition is true.
Hence printf statement will print: Start

Due to continue keyword program control will
come at the beginning of the for loop and value of
variable i will be:
i += 3
i=i+3=3

Second iteration:
i=3

variable i will be:
i += 3
i=i+3=6
Third iteration:
i=3

variable i will be:
i += 3
i=i+3=9

fourth iteration:
i=6
i < x i.e. 9 < 9 i.e. if loop condition is false.
Hence program control will come out of the for loop.

#include<stdio.h>
int main(){

static int i;

for(++i;++i;++i) {

printf("%d ",i);

if(i==4) break;

}
return 0;
}
Hint :- Value of Static int in c by default is 0.

ANS :- 2 4
Reason :- Default value of static int variable in c is
zero. So, initial value of variable i = 0

First iteration:
For loop starts value: ++i i.e. i = 0 + 1 = 1
For loop condition: ++i i.e. i = 1 + 1 = 2 i.e. loop
condition is true. Hence printf statement will print2

Loop incrimination: ++I i.e. i = 2 + 1 =3
Second iteration:
For loop condition: ++i i.e. i = 3 + 1 = 4 i.e. loop
condition is true. Hence printf statement will print
4.

Since is equal to for so if condition is also true.
But due to break keyword program control will
come out of the for loop.

#include<stdio.h>
int main(){
int i=1;
for(i=0;i=-1;i=1) {
printf("%d ",i);
if(i!=1) break;
}
return 0;
}

ANS :- -1
Reason :- Initial value of variable i is 1.
First iteration:
For loop initial value: i = 0
For loop condition: i = -1 . Since -1 is non- zero
number. So loop condition true. Hence printf
function will print value of variable i i.e. -1
Since variable i is not equal to 1. So, if condition is
true. Due to break keyword program control will
come out of the for loop.


#include<stdio.h>
int main(){
for(;;) {
printf("%d ",10);
}
return 0;
}

ANS :- Infinite Loop
Reason :- In for loop each part is optional.

What will be the output ?

include<stdio.h>
int main(){
int i;
for(i=0;i<=5;i++);
printf("%d",i);
return 0;
}

ANS :- 6
Reason :- Its possible for loop without any body

Finite or Infinite????

#include<stdio.h>
int main(){
char c=125;
do
printf("%d ",c);
while(c++);
return 0;
}

ANS :- Finite times

Reason :- If we will increment the char variable c
it will increment as:

126,127,-128,-127,126 . . . . , 3, 2, 1, 0
When variable c = 0 then loop will terminate.

3.Functions and Program Structures
• What is function in C programming?
• Definition
Function is block or part of program. When any
program is very long or same code is repeating
many times then we try to cut the program in
different parts (or blocks) so that whole
program became more understandable, easier
to debug (error checking) and size of code will
be lesser.

Syntax of Function :-
// Function Declaration
<return_type> <function_name>(<parameters>,…);

//Function Defination :-
<return_type> <function_name>(<parameters>,…){
Statement 1;
Statement 2;
return expression;
}

Simple example of function structure
int sum (int,int); //function declaration
void main(){
int p;
p=sum(3,4); //function call
printf(“%d”,sum);
}
int sum( int a,int b) //function definition{
int s; //function body
s=a+b;
return s; //function returning a value }

There are Rules for Function naming…Please chk
them out…I leave this as exercise to you…

Return type of function in c programming:-

return is keyword of c. When the control reaches
to the return keyword it immediately terminates
the execution of that function and transfer the
control to the calling function.

void dev();
void main(){
clrscr();
printf("onen");
dev();
printf("twon");
getch();
}
void dev(){
printf("threen");
return;
printf("fourn");
}

ANS :- one three two
As after return nothing wud be executed

Primitive data type.
Primitive data types are: char, int, float, double,
void
Examples:
a. function which is returning char data type
b. function which is returning int data type
c. function which is returning float data type
d. function which is returning double data type
e. function which is returning void data type

Derived data type.
Derived data types are: array, function, pointer
Examples:
a. Function which is returning array
b. function which is returning function
c. function which is returning pointer

User defined data type.
User defined data types are: structure, union,
enum
Examples:
a. Function which is returning structure
b. Function which is returning union
c. Function which is returning enum

Function can return only one value at time…
Storage classes allowed with return type are
static, extern, typedef i.e. we cannot use auto and
register storage class with the return type of any
function.

For eg

auto int tcs(int);
void main(){
int a=5;
a=tcs(a);
printf("%d",a);
}

auto int tcs(int x){

return x++;

}

Output: Compilation error

In return type we can use modifier like short, long, signed, unsigned, extern,
static, const, volatile etc.

long unsigned static const ddlg(){
static const long unsigned a=0101; // This is octal number….
return a;

}

void main(){

long number;

number=ddlg();

printf("%X",number); // %x – Hexadecimal equivalent

}

Output:41

Parameter or argument of function

Parameter of function can be:

1. Primitive data type.

2. Derived data type.

3. User defined data type.

4. Ellipsis i.e. variable number of parameter.

float sachin(int x){
float r=(float) x;
return r;
}
void main(){
float f;
f=sachin(33);

printf("%f",f);

}

Output : 33.000000

void main(){

float f;
f=sachin(33);
printf("%f",f);

}


float r=(float)x;

return r;

}

Output : Compilation error

float sachin(int);

void main(){
float f;
f=sachin(33);

printf("%f",f);

}


float r=(float)x;

return r;

}

Output: 33.000000

typedef float kp (int,char);

void main(){

float num,num1,num2;

kp a,b;

num1=a(5,'a');

num2=b(6,'0');

num=num1+num2;

printf("%f",num);

}

float a(int x, char y){

x=x+y;

return (float)x;

}

float b(int p,char q){

p=q-p;

return p;

}

Output: 144.000000

void main(){

float num,num1,num2;

num1=a(5,'a');

num2=b(6,'0');

num=num1+num2;

printf("%f",num);

}

float a(int x, char y){

x=x+y;

return (float)x;

}

float b(int p,char q){

p=q-p;

return p;

}

Output: Compilation error

Remember this For interview that
Function’s declaration doesn’t reserve any
memory space.

Function Recursion in C

Calling of same function from its function body is
known as function recursion. It is alternative of
loop. Any c program which is possible using loop
it must be possible using function recursion.

Find the sum of all even numbers from 0 to 20 using
function recursion.

Program:

void main(){

int total;

total=sum(2);

printf("%d",total);

}

int sum(int i){

static int even=0; // between successive calls we have to make sure even
becomes zero so we use static……

if(i<=20){

even=even+i;

sum(i+2); //calling same function

}

return even;

}

Output: 110

It is very difficult to understand the execution as
well as to write the function recursion program.

If any person is writing such program directly he
may be memorized that program.

Now note down the steps for writing the
program…

Step 1: Write the same program using while loop and
function. Here function is sum.

void main(){

int total;

total=sum(2);

printf("%d",total);

}

int sum(int i){

int even=0;

while(i<=20){

even=even+i;

i=i+2;

}

return even;

}

Step 2: Make local variable even as static variable

int sum(int i){

static int even=0;

while(i<=20){

even=even+i;

i=i+2;

}

return even;

}

Step 3: Replace while keyword by if keyword.

int sum(int i){

static int even=0;

if(i<=20){

even=even+i;

i=i+2;

}

return even;

}

Step 4: Since here variable i has used in condition checking. So
replace the statement i=i+2 by sum(i+2).

int sum(int i){

staic int even=0;

if(i<=20){

even=even+i;

sum(i+2);

}

return even;

}

Points to note about Recursion are :-
It is very slow process.

One problem with function recursion is it creates a
function frame in each function call. This makes
program very slow. This is main reason to
introduce for, while and do-while loop in c event
that it is also possible by using function recursion.

We cannot use break keyword in function
recursion.

Keyword break can be use to stop any loop. Since
function recursion is no a loop .So, we cannot use
break and continue keyword.

We can not use goto keyword to switch the
control from one function to another function.

Nesting of Function calls :-

If we are calling any function inside another
function call is known as nesting function call.
Sometime it converts a difficult program in easy
one.

For eg :-

Find the maximum number among five different integers using
nested function call.

Answer:

int max(int x,int y){return x>y?x:y;}

void main(){

int m;

m=max(max(4,max(11,6)),max(10,5));

printf("%d",m);

}

How to calculate size of a function in c?
Answer:
Size of any function is calculated as:
Size of function = Size of all local variable which
has declared in function + Size of those global
variables which has used in function+ Size of all
its parameter+ Size of returned value if it is an
address.

There are two types of function parameter standard:

1. ANSI standard

In this standard function definition is written as

int calculate(int a, int b){

int c;

c=a+b;

return c;

}

This standerd is also called as modern style.

2. Old Standard

int calculate(a, b)

int a,b;

{

int c;

c=a+b;

return c;

}

This standard is also called as old style.You should also known this style if
you want to read old c code.

4.Pointers — Before and After
There's a lot of nice, tidy code you can write without
knowing about pointers. But once you learn to use the
power of pointers, you can never go back. There are
too many things that can only be done with pointers.
But with increased power comes increased
responsibility. Pointers allow new and more ugly types
of bugs, and pointer bugs can crash in random ways
which makes them more difficult to debug
Nonetheless, even with their problems, pointers are an
irresistibly powerful programming construct.

The & operator :- Reference to

Last Lecture on Saturday….

We will do some 10-12 theory interview
questions and answers….and it will be over..no
more Subah uthna and no more pain…I hope you
liked my teaching…

Thanks for Attending the Series….

Why n++ executes faster than n+1 ?

The expression n++ requires a single machine
instruction such as INR to carry out the increment
operation whereas, n+1 requires more instructions
to carry out this operation.

What is C language?

The C programming language is a standardized
programming language developed in the early 1970s by
Ken Thompson and Dennis Ritchie for use on the UNIX
operating system. It has since spread to many other
operating systems, and is one of the most widely used
programming languages. C is prized for its efficiency, and
is the most popular programming language for writing
system software, though it is also used for writing
applications.

What is the main difference between
STRUCTURE and UNION?
1.]
important difference is in the size allocated to a
structure and an union. for eg:
struct example {
int integer;
float floating_numbers; }

the size allocated here is sizeof(int)+sizeof(float);

where as
in an union
union example {
int integer;
float floating_numbers;
}
size allocated is the size of
the highest member. so size is=sizeof(float);

2 . if we declare two structure variables as
struct strct1 x y;
then the two structure variables x and y have
different memory location.
But we declared tow unio variables as
union uni1 x y;
then the two union variables x and y have
same memory location.

Gud sites
• www.flazx.com

• www.codeproject.com

• www.academicearth.org

• www.securitytube.net

Thank You Very Much for attending the series….

If you wish to contact me :-
Mobile :- 9028199481
Email :- nanoketan@gmail.com
Blog :- www.nanoketya.blogspot.com
Facebook :- Ketan Paithankar

ALL THE BEST FOR YOUR LIFE………

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