Frequently asked C interview questions with answers

Introduction:
contains 50 frequently asked C interview questions with answers. A must have
learning resource for interview takers.

1. What does a static variable mean?
A static variable is a special variable that is stored in the data segment unlike the
default automatic variable that is stored in stack. A static variable can be initialised
by using keyword static before variable name.
For Example:
static int a = 5;
A static variable behaves in a different manner depending upon whether it is a global
variable or a local variable. A static global variable is same as an ordinary global
variable except that it cannot be accessed by other files in the same program /
project even with the use of keyword extern. A static local variable is different from
local variable. It is initialised only once no matter how many times that function in
which it resides is called. It may be used as a count variable.
Example:
void count(void) {
static int count1 = 0;
int count2 = 0;
count1++;
count2++;
printf("\nValue of count1 is %d Value of count2 is %d", count1,
count2);
}
//In Main function:
main() {
count();
count();
count();
 
}
Output would be:
Value of count1 is 1 Value of count2 is 1
Value of count1 is 2 Value of count2 is 1
Value of count1 is 3 Value of count2 is 1

2. What is a pointer?
A pointer is a special variable in C language meant just to store address of any other
variable or function. Pointer variables unlike ordinary variables cannot be operated
with all the arithmetic operations such as '*','%' operators. It follows a special
arithmetic called as pointer arithmetic.
A pointer is declared as:
int *ap;
int a = 5;
In the above two statements an integer a was declared and initialized to 5. A pointer
to an integer with name ap was declared.
Next before ap is used
ap=&a;
This operation would initialize the declared pointer to int. The pointer ap is now said
to point to a.
Operations on a pointer:
Dereferencing operator ' * ':
This operator gives the value at the address pointed by the pointer . For example
after the above C statements if we give
printf("%d",*ap);
Actual value of a that is 5 would be printed. That is because ap points to a.
Addition operator ' + ': Pointer arithmetic is different from ordinary arithmetic.
Expression ap=ap+1; Would not increment the value of ap by one byte but would
increment it by the number of bytes of the data type it is pointing to. Here ap is
pointing to an integer variable hence ap is incremented by 2 or 4 bytes depending
upon the compiler.

3. What is a structure?
A structure is a collection of pre-defined data types to create a user-defined data
type. Let us say we need to create records of students. Each student has three
fields:
int roll_number;
char name[30];
int total_marks;
This concept would be particularly useful in grouping data types. You could declare a
structure student as:
struct student {
int roll_number;
char name[30];
int total_marks;
} student1, student2;
The above snippet of code would declare a structure by name student and it
initializes two objects student1, student2. Now these objects and their fields could
be accessed by saying student1.roll_number for accesing roll number field of
student1 object Similarly student2.name for accessing name field of student2
object.

4. How to print below pattern?
1
2 3
4 5 6
7 8 9 10
Program:
#include
main() {
int i, j, ctr = 1;
for (i = 1; i < 5; i++) {
for (j = 1; j <= i; j++)
printf("%2d ", ctr++);
printf("\n");
}
}
Explanation:
There are two loops, a loop inside another one. Outer loop iterates 5 times. Inner
loop iterates as many times as current value of i. So for first time outer loop is
executed, inner loop is executed once. Second time the outer loop is entered, inner
loop is executed twice and so on. And every time the program enters inner loop,
value of variable ctr is printed and is incremented by 1. %2d ensures that the
number is printed in two spaces for proper alignment.

5. How to swap two numbers using bitwise operators?
Program:
#include
main() {
int i = 65;
int k = 120;
printf("\n value of i=%d k=%d before swapping", i, k);
i = i ^ k;
k = i ^ k;
i = i ^ k;
printf("\n value of i=%d k=%d after swapping", i, k);
}
Explanation:
i = 65; binary equivalent of 65 is 0100 0001
k = 120; binary equivalent of 120 is 0111 1000
i = i^k;
i...0100 0001
k...0111 1000
---------
val of i = 0011 1001
---------
k = i^k
i...0011 1001
k...0111 1000
---------
val of k = 0100 0001 binary equivalent of this is 65
---------(that is the initial value of i)
i = i^k
i...0011 1001
k...0100 0001
---------
val of i = 0111 1000 binary equivalent of this is 120
---------(that is the initial value of k)

6. What is recursion? Write a program using recursion (factorial)?
Recursion: A function is called 'recursive' if a statement within the body of a
function calls the same function. It is also called 'circular definition'. Recursion is
thus a process of defining something in terms of itself.
Program: To calculate the factorial value using recursion.
#include
int fact(int n);
main() {
int x, i;
printf("Enter a value for x: \n");
scanf("%d", &x);
i = fact(x);
printf("\nFactorial of %d is %d", x, i);
}
int fact(int n) {
/* n=0 indicates a terminating condition */
if (n <= 0) {
return (1);
} else {
/* function calling itself */
return (n * fact(n - 1));
/*n*fact(n-1) is a recursive expression */
}
}
Output:
Enter a value for x:
4
Factorial of 4 is 24
Explanation:
fact(n) = n * fact(n-1)
If n=4
fact(4) = 4 * fact(3) there is a call to fact(3)
fact(3) = 3 * fact(2)
fact(2) = 2 * fact(1)
fact(1) = 1 * fact(0)
fact(0) = 1
fact(1) = 1 * 1 = 1
fact(2) = 2 * 1 = 2
fact(3) = 3 * 2 = 6
Thus fact(4) = 4 * 6 = 24
Terminating condition(n <= 0 here;) is a must for a recursive program. Otherwise
the program enters into an infinite loop.

7. To which numbering system, can the binary number 1101100100111100 be
easily converted to?
1101100100111100 can be easily converted to hexadecimal numbering system.
Hexa-decimal integer constants consist of combination of digits from 0 to 9 and
alphabets 'A' to 'F'. The alphabets represent numbers 10 to 15 respectively. Hexa-
decimal numbers are preceeded by '0x'.
1101,1001,0011,1100
1101 = D
1001 = 9
0011 = 3
1100 = C
1101,1001,0011,1100 = 0xD93C
Thus the given binary number 1101100100111100 in hexadecimal form is 0xD93C

8. What are the differences between structures and unions?
Structures and Unions are used to store members of different data types.
STRUCTURE
 UNION
a)Declaration:
 a)Declaration:
struct
{
data type member1;
data type member2;
};
union
{
data type member1;
data type member2;
};
b)Every structure member is
allocated memory when a structure
variable is defined.
 b)The memory equivalent to the largest item is
allocated commonly for all members.
Example:
Example:
union emp1 {
struct emp {
char name[5];
char name[5];
int age;
float sal;
};
int age;
float sal;
};
union emp1 e2;
struct emp e1;
Memory allocated to a union is equal to size of
the largest member. In this case, float is the
largest-sized data type. Hence memory allocated
to this union is 4 bytes.
Memory allocated for structure is
1+2+4=7 bytes. 1 byte for name,
2 bytes for age and 4 bytes for sal.
c)All structure variables can be
initialized at a time
 c)Only one union member can be initialized at a
time
struct st {
union un {
int a;
float b;
};
int a;
float b;
};
struct st s = { .a=4, .b=10.5
};
Structure is used when all members
are to be independently used in a
program.
union un un1 = { .a=10 };
Union is used when members of it are not
required to be accessed at the same time.

9. What are the advantages of using unions?
Union is a collection of data items of different data types. It can hold data of only
one member at a time though it has members of different data types. If a union has
two members of different data types, they are allocated the same memory. The
memory allocated is equal to maximum size of the members. The data is interpreted
in bytes depending on which member is being accessed.
Example:
union pen {
char name;
float point;
};
Here name and point are union members. Out of these two variables, 'point' is
larger variable which is of float data type and it would need 4 bytes of memory.
Therefore 4 bytes space is allocated for both the variables. Both the variables have
the same memory location. They are accessed according to their type. Union is
efficient when members of it are not required to be accessed at the same time.

10. What is scope & storage allocation of global and extern variables? Explain
with an example
Extern variables: belong to the External storage class and are stored in the main
memory. extern is used when we have to refer a function or variable that is
implemented in other file in the same project. The scope of the extern variables is
Global.
Example:
//program in file f1.c
#include
extern int x;
main() {
printf("value of x %d", x);
}
//program in file f2.c
int x = 3;
Here, the program written in file f1.c has the main function and reference to variable
x. The file f2.c has the declaration of variable x. The compiler should know the
datatype of x and this is done by extern definition.
Global variables: are variables which are declared above the main( ) function.
These variables are accessible throughout the program. They can be accessed by all
the functions in the program. Their default value is zero.
Example:
#include
int x = 0;/* variable x is a global variable */
/* It can be accessed throughout the program */
void increment(void) {
x = x + 1;
printf("\n value of x: %d", x);
}
main() {
printf("\n value of x: %d", x);
increment();
}
11. What is scope & storage allocation of static, local and register variables?
Explain with an example.
Register variables: belong to the register storage class and are stored in the CPU
registers. The scope of the register variables is local to the block in which the
variables are defined. The variables which are used for more number of times in a
program are declared as register variables for faster access.
Example: loop counter variables.
register int y=6;
Static variables: Memory is allocated at the beginning of the program execution
and it is reallocated only after the program terminates. The scope of the static
variables is local to the block in which the variables are defined.
Example:
void decrement
{
static int a=5;
a--;
printf("%d", a);
}
Here 'a' is initialized only once. Every time this function is called, 'a' does not get
initialized. so output would be 4 3 2 etc.,
Local variables: are variables which are declared within any function or a block.
They can be accessed only by function or block in which they are declared. Their
default value is a garbage value.

12. What is Pass by Value? Write a C program showing this concept.
Pass by Value: In this method, the value of each of the actual arguments in the
calling function is copied into corresponding formal arguments of the called function.
In pass by value, the changes made to formal arguments in the called function have
no effect on the values of actual arguments in the calling function.
Example:
#include
swap(int x, int y) {
int t;
t = x;
x = y;
y = t;
}
main() {
int m = 10, n = 20;
printf("\n Before executing swap m=%d n=%d", m, n);
swap(m, n);
printf("\n After executing swap m=%d n=%d", m, n);
}
Output:
Before executing swap m=10 n=20
After executing swap m=10 n=20
Explanation:
In the main function, value of variables m, n are not changed though they are
passed to function 'swap'. Swap function has a copy of m, n and hence it can not
manipulate the actual value of arguments passed to it.

13. What is Pass by Reference? Write a C program showing this concept. Pass
by Reference: In this method, the addresses of actual arguments in the calling
function are copied into formal arguments of the called function. This means that
using these addresses, we would have an access to the actual arguments and hence
we would be able to manipulate them. Pass by reference is accomplished using
pointers.
Example:
#include
/* function definition */
void swap(int *x, int *y) {
int t;
t = *x; /* assign the value at address x to t */
*x = *y; /* put the value at y into x */
*y = t; /* put the value at to y */
}
main() {
int m = 10, n = 20;
printf("\n Before executing swap m=%d n=%d", m, n);
swap(&m, &n);
printf("\n After executing swap m=%d n=%d", m, n);
}
Output:
Before executing swap m=10 n=20
After executing swap m=20 n=10
Explanation:
In the main function, address of variables m, n are sent as arguments to the
function 'swap'. As swap function has the access to address of the arguments,
manipulation of passed arguments inside swap function would be directly reflected
in the values of m, n.

14. What is an Enumeration?
Enumeration is a data type. We can create our own data type and define values that
the variable can take. This can help in making program more readable. enum
definition is similar to that of a structure.
Example: consider light_status as a data type. It can have two possible values - on
or off.
enum light_status
{
on, off;
};
enum light_status bulb1, bulb2;
/* bulb1, bulb2 are the variables */
Declaration of enum has two parts:
a) First part declares the data type and specifies the possible values, called
'enumerators'.
b) Second part declares the variables of this data type.
We can give values to these variables:
bulb1 = on;
bulb2 = off;

15. What is the use of typedef?
typedef declaration helps to make source code of a C program more readable. Its
purpose is to redefine the name of an existing variable type. It provides a short and
meaningful way to call a data type. typedef is useful when the name of the data
type is long. Use of typedef can reduce length and complexity of data types.
Note: Usually uppercase letters are used to make it clear that we are dealing with
our own data type.
Example:
struct employee {
char name[20];
int age;
};
struct employee e;
The above declaration of the structure would be easy to use when renamed using
typedef as:
struct employee {
char name[20];
int age;
};
typedef struct employee EMP;
EMP e1, e2;

16. What are register variables? What are advantages of using register
variables?
Register variables are stored in the CPU registers. Its default value is a garbage
value. Scope of a register variable is local to the block in which it is defined. Lifetime
is till control remains within the block in which the register variable is defined.
Variable stored in a CPU register can always be accessed faster than the one that is
stored in memory. Therefore, if a variable is used at many places in a program, it is
better to declare its storage class as register
Example:
register int x=5;
Variables for loop counters can be declared as register. Note that register keyword
may be ignored by some compilers.

17. What are storage memory, default value, scope and life of Automatic and
Register storage class?
1. Automatic storage class:
Storage : main memory.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till control remains within the block.
2. Register storage class:
Storage : cpu registers.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till control remains within the block.

18. What are storage memory, default value, scope and life of Static and
External storage class?
1. Static storage class :
Storage : main memory
Default value : zero
Scope : local to the block in which the variable is defined
lifetime : till the value of the variable persists between different
function calls.
2. External storage class:
Storage : main memory
Default value : zero
Scope : global
Lifetime : as long as the program execution doesn't come to an end.

19. What are the advantages of using pointers in a program?
Pointers are special variables which store address of some other variables.
Syntax: datatype *ptr;
Here * indicates that ptr is a pointer variable which represents value stored at a
particular address.
Example: int *p;
'p' is a pointer variable pointing to address location where an integer type is stored.
Advantages:
3. Pointers allow us to pass values to functions using call by reference. This is
useful when large sized arrays are passed as arguments to functions. A
function can return more than one value by using call by reference.
4. Dynamic allocation of memory is possible with the help of pointers.
5. We can resize data structures. For instance, if an array's memory is fixed, it
cannot be resized. But in case of an array whose memory is created out of
malloc can be resized.
6. Pointers point to physical memory and allow quicker access to data.

20. Which bitwise operator is suitable for checking whether a particular bit is
ON or OFF?
Bitwise AND operator.
Example: Suppose in byte that has a value 10101101 . We wish to check whether
bit number 3 is ON (1) or OFF (0) . Since we want to check the bit number 3, the
second operand for AND operation we choose is binary 00001000, which is equal to
8 in decimal.
Explanation:
ANDing operation :
10101101 original bit pattern
00001000 AND mask
---------
00001000 resulting bit pattern
The resulting value we get in this case is 8, i.e. the value of the second operand.
The result turned out to be a 8 since the third bit of operand was ON. Had it been
OFF, the bit number 3 in the resulting bit pattern would have evaluated to 0 and
complete bit pattern would have been 00000000. Thus depending upon the bit
number to be checked in the first operand we decide the second operand, and on
ANDing these two operands the result decides whether the bit was ON or OFF.
 

21. Which bit wise operator is suitable for turning OFF a particular bit in a
number?
Bitwise AND operator (&), one's complement operator(~)
Example: To unset the 4th bit of byte_data or to turn off a particular bit in a
number.
Explanation:
consider,
char byte_data= 0b00010111;
byte_data= (byte_data)&(~(1<<4));
EXPLANATION:
1 can be represented in binary as 0b00000001
(1<<4)
<< is a left bit shift operator, it shits the bit 1 by 4 places towards
left.
(1<<4) becomes 0b00010000
And ~ is the one's complement operator in C language.
So ~(1<<4) = complement of 0b00010000
= 0b11101111
replacing value of byte_data and ~(1<<4) in
(byte_data)&(~(1<<4));
we get
(0b00010111) & (0b11101111)
Perform AND operation to below bytes.
00010111
11101111
-----------
00000111
-----------
Thus the 4th bit is unset.

22. What do the 'c' and ' v ' in argc and argv stand for? Explain their purpose?
In C, we can supply arguments to 'main' function. The arguments that we pass to
main ( ) at command prompt are called command line arguments. These arguments
are supplied at the time of invoking the program.
The main ( ) function can take arguments as: main(int argc, char *argv[]) { }
The first argument argc is known as 'argument counter'. It represents the number
of arguments in the command line. The second argument argv is known as
'argument vector'. It is an array of char type pointers that points to the command
line arguments. Size of this array will be equal to the value of argc.
Example: at the command prompt if we give:
C:\> fruit.exe apple mango
then
argc would contain value 3
argv [0] would contain base address of string " fruit.exe" which is the command
name that invokes the program.
argv [1] would contain base address of string "apple"
argv [2] would contain base address of string "mango"
here apple and mango are the arguments passed to the program fruit.exe
Program:
#include
main(int argc, char *argv[]) {
int n;
printf("Following are the arguments entered in the command line");
for (n = 0; n < argc; n++) {
printf("\n %s", argv[n]);
}
printf("\n Number of arguments entered are\n %d", argc);
}
Output:
Following are the arguments entered in the command line
C:\testproject.exe
apple
mango
Number of arguments entered are 3

23. What are the differences between malloc() and calloc()?
Allocation of memory at the time of execution is called dynamic memory allocation.
It is done using the standard library functions malloc() and calloc(). It is defined in
"stdlib.h".
malloc(): used to allocate required number of bytes in memory at runtime. It takes
one argument, viz. size in bytes to be allocated.
Syntax:
void * malloc(size_t size);
 Example:
a = (int*) malloc(4);
4 is the size (in bytes) of memory to be allocated.
calloc(): used to allocate required number of bytes in memory at runtime. It needs
two arguments viz.,
1. total number of data and
2. size of each data.
Syntax:
void * calloc(size_t nmemb, size_t size);
Example:
a = (int*) calloc(8, sizeof(int));
Here sizeof indicates the size of the data type and 8 indicates that we want to
reserve space for storing 8 integers.
Differences between malloc() and calloc() are:
1. Number of arguments differ.
2. By default, memory allocated by malloc() contains garbage values. Whereas
memory allocated by calloc() contains all zeros.

24. Where are the auto variables stored?
Main memory and CPU registers are the two memory locations where auto variables
are stored. Auto variables are defined under automatic storage class. They are
stored in main memory. Memory is allocated to an automatic variable when the
block which contains it is called and it is de-allocated at the completion of its block
execution.
Auto variables:
Storage : main memory.
Default value : garbage value.
Scope : local to the block in which the variable is defined.
Lifetime : till the control remains within the block in which the variable is
defined.

25. Out of fgets( ) and gets( ) which function is safer to use and why?
Out of functions fgets( ) and gets( ), fgets( ) is safer to use. gets( ) receives a string
from the keyboard and it is terminated only when the enter key is hit. There is no
limit for the input string. The string can be too long and may lead to buffer overflow.
Example:
gets(s) /* s is the input string */
Whereas fgets( ) reads string with a specified limit, from a file and displays it on
screen.The function fgets( ) takes three arguments.
First argument : address where the string is stored.
Second argument : maximum length of the string.
Third argument : pointer to a FILE.
Example:
fgets(s,20,fp); /* s: address of the string, 20: maximum length of string, fp: pointer
to a file */
The second argument limits the length of string to be read. Thereby it avoids
overflow of input buffer. Thus fgets( ) is preferable to gets( ).

26. How can you increase the size of a dynamically allocated array?
realloc(): This function is used to increase or decrease the size of any dynamic
memory which is allocated using malloc() or calloc() functions.
Syntax: void *realloc(void *ptr, size_t newsize);
The first argument 'ptr' is a pointer to the memory previously allocated by the
malloc or calloc functions. The second argument 'newsize' is the size in bytes, of a
new memory region to be allocated by realloc. This value can be larger or smaller
than the previously allocated memory. The realloc function adjusts the old memory
region if newsize is smaller than the size of old memory.
If the newsize is larger than the existing memory size, it increases the size by
copying the contents of old memory region to new memory region. The function
then deallocates the old memory region. realloc function is helpful in managing a
dynamic array whose size may change during execution.
Example: a program that reads input from standard input may not know the size of
data in advance. In this case, dynamically allocated array can be used so that it is
possible allocate the exact amount of memory using realloc function.

27. Write a program to check whether a given number is even or odd. Program:
#include
main() {
int a;
printf("Enter a: \n");
scanf("%d", &a);
/* logic */
if (a % 2 == 0) {
printf("The given number is EVEN");
} else {
printf("The given number is ODD");
}
}
Output:
Enter a: 2
The given number is EVEN
Explanation with examples:
Example 1: If entered number is an even number
Let value of 'a' entered is 4
if(a%2==0) then a is an even number, else odd.
i.e. if(4%2==0) then 4 is an even number, else odd.
To check whether 4 is even or odd, we need to calculate (4%2).
/* % (modulus) implies remainder value. */
/* Therefore if the remainder obtained when 4 is divided by 2 is 0,
then 4 is even. */
4%2==0 is true
Thus 4 is an even number.
Example 2: If entered number is an odd number.
Let value of 'a' entered is 7
if(a%2==0) then a is an even number, else odd.
i.e. if(7%2==0) then 4 is an even number, else odd.
To check whether 7 is even or odd, we need to calculate (7%2).
7%2==0 is false /* 7%2==1 condition fails and else part is executed */
Thus 7 is an odd number.

28. Write a program to find the greatest of three numbers.
Program:
#include
main() {
int a, b, c;
printf("Enter a,b,c: \n");
scanf("%d %d %d", &a, &b, &c);
if (a > b && a > c) {
printf("a is Greater than b and c");
} else if (b > a && b > c) {
printf("b is Greater than a and c");
} else if (c > a && c > b) {
printf("c is Greater than a and b");
} else {
printf("all are equal or any two values are equal");
}
}
Output:
Enter a,b,c: 3 5 8
c is Greater than a and b
Explanation with examples:
consider three numbers a=5,b=4,c=8
if(a>b && a>c) then a is greater than b and c
now check this condition for the three numbers 5,4,8 i.e.
if(5>4 && 5>8) /* 5>4 is true but 5>8 fails */
so the control shifts to else if condition
else if(b>a && b>c) then b is greater than a and c
now checking this condition for 5,4,8 i.e.
else if(4>5 && 4>8) /* both the conditions fail */
now the control shifts to the next else if condition
else if(c>a && c>b) then c is greater than a and b
now checking this condition for 5,4,8 i.e.
else if(8>5 && 8>4) /* both conditions are satisfied */
Thus c is greater than a and b.

29. Write a program to check whether a given number is a prime.
A prime number is a natural number that has only one and itself as factors.
Examples: 2, 3, 5, 7,… are prime numbers.
Program:
#include
main() {
int n, i, c = 0;
printf("Enter any number n: \n");
scanf("%d", &n);
/*logic*/
for (i = 1; i <= n; i++) {
if (n % i == 0) {
c++;
}
}
if (c == 2) {
printf("n is a Prime number");
} else {
printf("n is not a Prime number");
}
}
Output:
Enter any number n: 7
n is Prime
Explanation with examples:
consider a number n=5
for(i=0;i<=n;i++) /* for loop is executed untill the n value equals i
*/
i.e. for(i=0;i<=5;i++) /* here the for loop is executed untill i is
equal to n */
1st iteration: i=1;i<=5;i++
here i is incremented i.e. i value for next iteration is 2
now if(n%i==0) then c is incremented
i.e.if(5%1==0)then c is incremented, here 5%1=0 thus c is incremented.
now c=1;
2nd iteration: i=2;i<=5;i++
here i is incremented i.e. i value for next iteration is 3
now if(n%i==0) then c is incremented
i.e.if(5%2==0) then c is incremented, but 5%2!=0 and so c is not
incremented, c remains 1
c=1;
3rd iteration: i=3;i<=5;i++
here i is incremented i.e. i value for next iteration is 4
now if(n%i==0) then c is incremented
i.e.if(5%3==0) then c ic incremented, but 5%3!=0 and so c is not
incremented, c remains 1
c=1;
4th iteration: i=4;i<=5;i++
here i is incremented i.e. i value for next iteration is 5
now if(n%i==0) then c is incremented
i.e. if(5%4==0) then c is incremented, but 5%4!=0 and so c is not
incremented, c remains 1
c=1;
5th iteration: i=5;i<=5;i++
here i is incremented i.e. i value for next iteration is 6
now if(n%i==0) then c is incremented
i.e. if(5%5==0) then c is incremented, 5%5=0 and so c is incremented.
i.e. c=2
6th iteration: i=6;i<=5;i++
here i value is 6 and 6<=5 is false thus the condition fails and
control leaves the for loop.
now if(c==2) then n is a prime number
we have c=2 from the 5th iteration and thus n=5 is a Prime number.

30. Write a program to find the greatest among ten numbers.
Program:
#include
main() {
int a[10];
int i;
int greatest;
printf("Enter ten values:");
//Store 10 numbers in an array
for (i = 0; i < 10; i++) {
scanf("%d", &a[i]);
}
//Assume that a[0] is greatest
greatest = a[0];
for (i = 0; i < 10; i++) {
if (a[i] > greatest) {
greatest = a[i];
}
 
}
printf("\nGreatest of ten numbers is %d", greatest);
}
Output:
Enter ten values: 2 53 65 3 88 8 14 5 77 64 Greatest of ten numbers is 88
Explanation with example:
Entered values are 2, 53, 65, 3, 88, 8, 14, 5, 77, 64
They are stored in an array of size 10. let a[] be an array holding these values.
/* how the greatest among ten numbers is found */
Let us consider a variable 'greatest'. At the beginning of the loop, variable 'greatest'
is assinged with the value of first element in the array greatest=a[0]. Here variable
'greatest' is assigned 2 as a[0]=2.
Below loop is executed until end of the array 'a[]';.
for(i=0; i<10; i++)
{
if(a[i]>greatest)
{
greatest= a[i];
}
}
For each value of 'i', value of a[i] is compared with value of variable 'greatest'. If
any value greater than the value of 'greatest' is encountered, it would be replaced
by a[i]. After completion of 'for' loop, the value of variable 'greatest' holds the
greatest number in the array. In this case 88 is the greatest of all the numbers.

31. Write a program to swap two numbers using a temporary variable.
Swapping interchanges the values of two given variables.
Logic:
step1: temp=x;
step2: x=y;
step3: y=temp;
Example
if x=5 and y=8, consider a temporary variable temp.
step1: temp=x=5;
step2: x=y=8;
step3: y=temp=5;
Thus the values of the variables x and y are interchanged.
Program:
#include
main() {
int a, b, temp;
printf("Enter the value of a and b: \n");
scanf("%d %d", &a, &b);
printf("Before swapping a=%d, b=%d \n", a, b);
/*Swapping logic */
temp = a;
a = b;
b = temp;
printf("After swapping a=%d, b=%d", a, b);
}
Output:
Enter the values of a and b: 2 3
Before swapping a=2, b=3
After swapping a=3, b=2

32. Write a program to swap two numbers without using a temporary variable.
Swapping interchanges the values of two given variables.
Logic:
step1: x=x+y;
step2: y=x-y;
step3: x=x-y;
Example:
if x=7 and y=4
step1: x=7+4=11;
step2: y=11-4=7;
step3: x=11-7=4;
Thus the values of the variables x and y are interchanged.
Program:
#include
main() {
int a, b;
printf("Enter values of a and b: \n");
scanf("%d %d", &a, &b);
printf("Before swapping a=%d, b=%d", a,b n);
/*Swapping logic */
a = a + b;
b = a - b;
a = a - b;
printf("After swapping a=%d b=%d", a, b);
}
Output:
Enter values of a and b: 2 3
Before swapping a=2, b=3
The values after swapping are a=3 b=2

33. How to swap two numbers using bitwise operators?
Program:
#include
main() {
int i = 65;
int k = 120;
printf("\n value of i=%d k=%d before swapping", i, k);
i = i ^ k;
k = i ^ k;
i = i ^ k;
printf("\n value of i=%d k=%d after swapping", i, k);
}
Explanation:
i = 65; binary equivalent of 65 is 0100 0001
k = 120; binary equivalent of 120 is 0111 1000
i = i^k;
i...0100 0001
k...0111 1000
---------
val of i = 0011 1001
---------
k = i^k
i...0011 1001
k...0111 1000
---------
val of k = 0100 0001 binary equivalent of this is 65
---------(that is the initial value of i)
i = i^k
i...0011 1001
k...0100 0001
---------
val of i = 0111 1000 binary equivalent of this is 120
---------(that is the initial value of k)

34. Write a program to check whether a given number is a palindromic number.
If a number, which when read in both forward and backward way is same, then such
a number is called a palindrome number.
Program:
#include
main() {
int n, n1, rev = 0, rem;
printf("Enter any number: \n");
scanf("%d", &n);
n1 = n;
/* logic */
while (n > 0) {
rem = n % 10;
rev = rev * 10 + rem;
n = n / 10;
}
if (n1 == rev) {
printf("Given number is a palindromic number");
} else {
printf("Given number is not a palindromic number");
}
}
Output:
Enter any number: 121
Given number is a palindrome
Explanation with an example:
consider a number n=121, reverse=0, remainder;
number=121
now the while loop is executed /* the condition (n>0) is satisfied */
/* calculate remainder */
remainder of 121 divided by 10=(121%10)=1;
now reverse=(reverse*10)+remainder
=(0*10)+1 /* we have initialized reverse=0 */
=1
number=number/10
=121/10
=12
now the number is 12, greater than 0. The above process is repeated for
number=12.
remainder=12%10=2;
reverse=(1*10)+2=12;
number=12/10=1;
now the number is 1, greater than 0. The above process is repeated for
number=1.
remainder=1%10=1;
reverse=(12*10)+1=121;
number=1/10 /* the condition n>0 is not satisfied,control leaves the
while loop */
Program stops here. The given number=121 equals the reverse of the number. Thus
the given number is a palindrome number.

35. Write a program to check whether a given string is a palindrome.
Palindrome is a string, which when read in both forward and backward way is same.
Example: radar, madam, pop, lol, rubber, etc.,
Program:
#include
#include
main() {
char *string1;
char *string2;
printf("Enter a string: \n");
scanf("%s", string1);
//Copy original string to string2
string2 = strdup(string1);
//Reverse original string
string1 = strrev(string1);
//Compare string1, string2
if (strcmp(string1, string2)) {
printf("\n%s is not a palindrome", string2);
} else {
printf("\n%s is a palindrome", string2);
}
}
Output:
Enter a string: radar
"radar" is a palindrome
Explanation with example:
Entered string is "radar", store it into 'string1'
now string2= strdup(string1);
here string1(="radar") is copied into string2 using strdup function.
Hence string2="radar"; /* copy of string1 */
string1=strrev(string1);
Now string stored in variable 'string1' is reversed.
Reverse of string "radar" is "radar". So "radar" is stored in variable 'string1'.
string1= "radar" /* reverse of the string */
Now let us compare the original string and its reverse.
string1= "radar" /* reverse of the string */
string2= "radar" /* copy of the actual string */
Both string1 and string2 are equal, thus the given string is a palindrome.

36. Write a program in C to print "Hello World" without using semicolon
anywhere in the code.
Generally when we use printf("") statement, we have to use a semicolon at the end.
If printf is used inside an if condition, semicolon can be avoided.
Program: Program to print some thing with out using semicolon(;)
#include
int main(void) {
//(Length of string being printed)
if (printf("Hello World")) //prints Hello World and returns 11
{
//since 11>0,condition is true and cursor goes into the loop
}
}
Output:
Hello World
Explanation:
The if statement checks for condition whether the return value of printf("Hello
World") is greater than 0. printf function returns the length of the string printed.
Hence the statement if (printf("Hello World")) prints the string "Hello World".

37. Write a program in C to print a semicolon without using a semicolon
anywhere in the code.
Generally when use printf("") statement we have to use semicolon at the end.
If we want to print a semicolon, we use the statement: printf(";");
In above statement, we are using two semicolons. The task of printing a semicolon
without using semicolon anywhere in the code can be accomplished by using the
ascii value of ' ; ' which is equal to 59.
Program: Program to print a semicolon without using semicolon in the code.
#include
int main(void) {
//prints the character with ascii value 59, i.e., semicolon
if (printf("%c", 59)) {
//prints semicolon
}
}
Output:
;
Explanation:
If statement checks whether return value of printf function is greater than zero or
not. The return value of function call printf("%c",59) is 1. As printf returns the
length of the string printed. printf("%c",59) prints ascii value that corresponds to
59, that is semicolon(;). See complete list of ascii values.

38. Write a program in C to delete a specific line from a text file.
In this program, user is asked for a filename he needs to change. User is also asked
for the line number that is to be deleted. The filename is stored in 'filename'. The
file is opened and all the data is transferred to another file except that one line the
user specifies to delete.
Program: Program to delete a specific line.
#include
int main(void) {
FILE *fp1, *fp2;
//consider 40 character string to store filename
char filename[40];
char c;
int del_line, temp = 1;
//asks user for file name
printf("Enter file name: ");
//receives file name from user and stores in 'filename'
gets(filename);
//open file in read mode
fp1 = fopen(filename, "r");
c = getc(fp1);
//until the last character of file is obtained
while (c != EOF)
{
 printf("%c", c);
//print current character and read next character
c = getc(fp1);
}
//rewind
rewind(fp1);
printf(" \n Enter line number of the line to be deleted:");
//accept number from user.
scanf("%d", &del_line);
//open new file in write mode
fp2 = fopen("copy.c", "w");
c = getc(fp1);
while (c != EOF) {
c = getc(fp1);
if (c == '\n')
temp++;
//except the line to be deleted
if (temp != del_line)
{
//copy all lines in file copy.c
putc(c, fp2);
}
}
//close both the files.
fclose(fp1);
fclose(fp2);
//remove original file
remove(filename);
//rename the file copy.c to original name
rename("copy.c", filename);
printf("\n The contents of file after being modified are as
follows:\n");
fp1 = fopen(filename, "r");
c = getc(fp1);
while (c != EOF) {
printf("%c", c);
c = getc(fp1);
}
fclose(fp1);
system("pause");
}
Output:
Enter file name:abc.txt
hi.
hello
how are you?
I am fine
hope the same
Enter line number of the line to be deleted:4
The contents of file after being modified are as follows:
hi.
hello
how are you?
hope the same
press any key to continue. . .
Explanation:
In this program, user is asked for a filename that needs to be modified. Entered file
name is stored in a char array 'filename'. This file is opened in read mode using file
pointer 'fp1'. Character 'c' is used to read characters from the file and print them to
the output. User is asked for the line number in the file to be deleted. The file
pointer is rewinded back and all the lines of the file except for the line to be deleted
are copied into another file "copy.c". Now "copy.c" is renamed to the original
filename. The original file is opened in read mode and the modified contents of the
file are displayed on the screen.
 
39. Write a program in C to replace a specified line in a text file.
Program: Program to replace a specified line in a text file.
#include
int main(void) {
FILE *fp1, *fp2;
//'filename'is a 40 character string to store filename
char filename[40];
char c;
int del_line, temp = 1;
//asks user for file name
printf("Enter file name: ");
//receives file name from user and stores in 'filename'
gets(filename);
fp1 = fopen(filename, "r");
//open file in read mode
c = getc(fp1);
while (c != EOF) {
printf("%c", c);
c = getc(fp1); //print the contents of file .
}
//ask user for line number to be deleted.
printf(" \n Enter line number to be deleted and replaced");
scanf("%d", &del_line);
//take fp1 to start point.
rewind(fp1);
//open copy.c in write mode
fp2 = fopen("copy.c", "w");
c = getc(fp1);
while (c != EOF) {
if (c == '\n') {
temp++;
}
//till the line to be deleted comes,
//copy the content from one file to other
if (temp != del_line) {
putc(c, fp2);
} else //when the line to be deleted comes
{
 while ((c = getc(fp1)) != '\n') {
} //read and skip the line
//ask for new text
printf("Enter new text");
//flush the input stream
fflush(stdin);
putc('\n', fp2);
//put '\n' in new file
while ((c = getchar()) != '\n')
putc(c, fp2);
//take the data from user and place it in new file
fputs("\n", fp2);
temp++;
}
//continue this till EOF is encountered
c = getc(fp1);
}
//close both files
fclose(fp1);
fclose(fp2);
remove(filename);
//remove original file
rename("copy.c", filename);
//rename new file with old name
//opens the file in read mode
fp1 = fopen(filename, "r");
//reads the character from file
c = getc(fp1);
//until last character of file is encountered
while (c != EOF)
{
 printf("%c", c);
//all characters are printed
c = getc(fp1);
}
//close the file pointer
fclose(fp1);
system("pause");
}
Output:
Enter file name:abc.txt
hi.
hello
how are you?
hope the same
Enter line number of the line to be deleted and replaced:4
Enter new text: sayonara see you soon
hi.
hello
how are you?
sayonara see you soon
press any key to continue. . .
Explanation:
In this program, the user is asked to type the name of the file. The File by name
entered by user is opened in read mode. The line number of the line to be replaced
is asked as input. Next the data to be replaced is asked. A new file is opened in
write mode named "copy.c". Now the contents of original file are transferred into
new file and the line to be modified is deleted. New data is stored in its place and
remaining lines of the original file are also transferred. The copied file with modified
contents is replaced with the original file's name. Both the file pointers are closed
and the original file is again opened in read mode and the contents of the original
file is printed as output.

40. Write a program in C to find the number of lines in a text file.
Number of lines in a file can be determined by counting the number of new line
characters present.
Program: Program to count number of lines in a file.
#include
int main(void)
/* Ask for a filename and count number of lines in the file*/
{
 //a pointer to a FILE structure
FILE *fp;
int no_lines = 0;
//consider 40 character string to store filename
char filename[40], sample_chr;
//asks user for file name
printf("Enter file name: ");
//receives file name from user and
//stores in a string named 'filename'
gets(filename);
//open file in read mode
fp = fopen(filename, "r");
//get character from file and store in sample_chr
sample_chr = getc(fp);
while (sample_chr != EOF) {
//Count whenever sample_chr is '\n'
//i.e., new line is encountered
if (sample_chr == '\n')
{
//increment variable 'no_lines' by 1
no_lines=no_lines+1;
}
//take next character from file.
sample_chr = getc(fp);
}
fclose(fp); //close file.
printf("There are %d lines in %s \n", no_lines, filename);
system("pause");
}
Output:
Enter file name:abc.txt
There are 4 lines in abc.txt
press any key to continue. . .
Explanation:
In this program, name of the file to be read is taken as input. A file by the given
name is opened in read-mode using a File pointer 'fp'. Characters from the file are
read into a char variable 'sample_chr' with the help of getc function. If a new line
character('\n') is encountered, the integer variable 'no_lines' is incremented. If the
character read into 'sample_char' is not a new line character, next character is read
from the file. This process is continued until the last character of the file(EOF) is
encountered. The file pointer is then closed and the total number of lines is shown
as output.

41. (i)What are the differences between the C statements below:
char *str = "Hello";
char arr[] = "Hello";
(ii)Whether following statements get complied or not? Explain each
statement.
arr++;
*(arr + 1) = 's';
printf("%s",arr);
(i) char *str="Hello";
"Hello" is an anonymous string present in the memory. 'str' is a pointer variable
that holds the address of this string.
char arr[]="Hello";
This statement assigns space for six characters: 'H' 'e' 'l' 'l' 'o' '\0' . 'arr' is the
variable name assigned to this array of characters. Read more about the
differences.
str[4] and arr[4] also have different meanings.
str[4]: adds 4 to the value of 'str' and points to the address same as value of str
+ 4.
arr[4]: points to the fourth element in array named 'arr'.
(ii) 'arr' is variable name of an array. A variable name cannot be incremented or
decremented. Hence arr++ is an invalid statement and would result in a
compilation error.
*(arr+1)='s';
'arr' is the name of a character array that holds string "Hello". Usually, name of
an array points to its base address. Hence value of arr is same as &arr[0].
arr+1 is address of the next element: &arr[1]
Character 's' is assigned to the second element in array 'arr', thereby string
changes from "Hello" to "Hsllo".
printf("%s",arr );
This statement prints the string stored in character array 'arr'.

42. Explain the variable assignment in the declaration
int *(*p[10])(char *, char *);
It is an array of function pointers that returns an integer pointer. Each function
has two arguments which in turn are pointers to character type variable. p[0],
p[1],....., p[9] are function pointers. Read more about Function Pointers in C.
return type : integer pointer.
p[10] : array of function pointers
char * : arguments passed to the function
Program: Example program to explain function pointers.
#include
#include
int *(*p[10])(char *, char *);
//average function which returns pointer to
//integer whose value is average of ascii value
//of characters passed by pointers
int *average(char *, char *);
//function which returns pointer to integer whose value is
//sum of ascii value of characters passed by pointers
int *sum(char *, char *);
int retrn;
int main(void) {
int i;
for (i = 0; i < 5; i++) {
//p[0] to p[4] are pointers to average function.
p[i] = &average;
}
for (i = 5; i < 10; i++) {
//p[5] to p[9] are pointers to sum function
p[i] = ∑
}
char str[10] = "nodalo.com";
int *intstr[10];
for (i = 0; i < 9; i++) {
//upto p[4] average function is called, from p[5] sum is called.
intstr[i] = p[i](&str[i], &str[i + 1]);
if (i < 5) {
//prints the average of ascii of both characters
printf(" \n average of %c and %c is %d",
str[i], str[i + 1],*intstr[i]);
}
else {
//prints the sum of ascii of both characters.
printf(" \n sum of %c and %c is %d",
str[i], str[i + 1], *intstr[i]);
}
}
system("pause");
}
//function average is defined here
int *average(char *arg1, char *arg2) {
retrn = (*arg1 + *arg2) / 2;
return (&retrn);
}
//function sum is defined here
int *sum(char *arg1, char *arg2) {
retrn = (*arg1 + *arg2);
return (&retrn);
}
Output:
average of n and o is 110
average of o and d is 105
average of d and a is 98 average of d and a is 98
average of a and l is 102
average of l and o is 109
sum of o and . is 157
sum of . and c is 145
sum of c and o is 210
sum of o and m is 220
press any key to continue . . .
Explanation:
In this program p[10] is an array of function pointers. First five elements of p[10]
point to the function: int *average(char *arg1,char *arg2). Next five elements
point to the function int *sum(char *arg1,char *arg2). They return pointer to an
integer and accept pointer to char as arguments.
Function average:
int *average(char *arg1,char *arg2) This function finds the average of the two
values of the addresses passed to it as arguments and returns address of the
average value as an integer pointer.
Function sum:
int *sum(char *arg1,char *arg2) This function finds the sum of the two values of
the addresses passed to it as arguments and returns address of the sum value
as an integer pointer.

43. What is the value of sizeof(a) /sizeof(char *) in C code snippet below
char *a[4]={"sridhar","raghava","shashi","srikanth"}; explain
Explanation:
Here a[4] is an array which holds the address of strings. Strings are character
arrays themselves.
Memory required to store an address is 4 bits. So memory required to store 4
addresses is equal to 4*4=16 bits.
char *; is a pointer variable which stores the address of a char variable.
So sizeof(char *) is 4 bits. Therefore sizeof(a) /sizeof(char *) = 16/4 = 4 bytes.
Read more about sizeof operator in C.
 
44. Write a program in C that returns 3 numbers from a function.
A function in C can return only one value. If we want the function to return
multiple values, we need to create a structure variable, which has three
integer members and return this structure.
Read more about structures in C.
Program: Program with a function to return 3 values .
#include
//sample structure which has three integer variables.
struct sample {
int a, b, c;
};
//this is function which returns three values.
struct sample return3val(void) {
struct sample s1;
s1.a = 10;
s1.b = 20;
s1.c = 30;
//return structure s1, which means return s1.a ,s1.b and s1.c
return s1;
}
int main(void) {
struct sample accept3val;
//three values returned are accepted by structure accept3val.
accept3val = return3val();
//prints the values
printf(" \n %d", accept3val.a);
printf("\n %d", accept3val.b);
printf(" \n %d", accept3val.c);
getchar();
}
Output:
10
20
30.
Explanation:
In this program, we use C structure to return multiple values from a function.
Here we have a structure holding three int variables and a function which returns
it. 'return3val' is a function which assigns 10, 20, 30 to its integer variables and
returns this structure. In this program, 'accept3val' is a structure used to accept
the values returned by the function. It accepts those values and shows the
output.

45. In below code snippet:
struct Date
{
int yr;
int day;
int month;
} date1,date2;
date1.yr = 2004;
date1.day = 4;
date1.month = 12;
Write a function in C that assign values to date2. Arguments to the function
must be pointers to the structure Date and integer variables date, month,
year.
Date is structure with three int variables as members. set_date(..) is a function
used to assign values to the structure variable.
Program: Program to illustrate a function that assigns value to the structure.
#include
#include
//declare structure Date
struct Date {
int yr;
int day;
int month;
} date1, date2;
//declare function to assign date to structure variable
void set_date(struct Date *dte, int dt, int mnt, int year) {
dte->day = dt;
dte->yr = year;
dte->month = mnt;
}
int main(void) {
date1.yr = 2004;
date1.day = 4;
//assigning values one by one
date1.month = 12;
//assigning values in a single statement
set_date(&date2, 05, 12, 2008);
//prints both dates in date/month/year format
printf("\n %d %d %d ", date1.day, date1.month, date1.yr); printf("\n %d
%d %d ", date2.day, date2.month, date2.yr); system("pause");
}
Output:
4 12 2004
5 12 2008 press any key to continue. . .
Explanation:
Two variables of type Date are created and named 'date1', 'date2'. 'date2' is
assigned by using the function set_date(..). Address of 'date2' is passed to
set_date function. Read more about pointers to Structures.

46. What are header files? Are functions declared or defined in header files?
Functions and macros are declared in header files. Header files would be
included in source files by the compiler at the time of compilation.
Header files are included in source code using #include
directive.#include includes all the declarations present in the header
file 'some.h'.
A header file may contain declarations of sub-routines, functions, macros and
also variables which we may want to use in our program. Header files help in
reduction of repetitive code.
Syntax of include directive:
#include //includes the header file stdio.h, standard input output header
into the source code
Functions can be declared as well as defined in header files. But it is
recommended only to declare functions and not to define in the header files.
When we include a header file in our program we actually are including all the
functions, macros and variables declared in it.
In case of pre-defined C standard library header files ex(stdio.h), the functions
calls are replaced by equivalent binary code present in the pre-compiled
libraries. Code for C standard functions are linked and then the program is
executed. Header files with custom names can also be created. Read more
about header files
Program: Custom header files example
/****************
Index: restaurant.h
****************/
int billAll(int food_cost, int tax, int tip);
/****************
Index: restaurant.c
****************/
int billAll(int food_cost, int tax, int tip) {
int result;
result = food_cost + tax + tip;
return result;
}
/****************
Index: main.c
****************/
#include
#include
int main() {
int food_cost, tax, tip;
food_cost = 50;
tax = 10;
tip = 5;
return 0;
}

47. What is the difference between the functions strdup and strcpy in C?
strcpy function: copies a source string to a destination defined by user. In
strcpy function both source and destination strings are passed as arguments.
User should make sure that destination has enough space to accommodate the
string to be copied.
'strcpy' sounds like short form of "string copy".
Syntax:
strcpy(char *destination, const char *source);
Source string is the string to be copied and destination string is string into which
source string is copied. If successful, strcpy subroutine returns the address of
the copied string. Otherwise, a null pointer is returned.
Program: Example program.
#include
#include
int main() {
char myname[10];
//copy contents to myname
strcpy(myname, "nodalo");
//print the string
puts(myname);
return 0;
}
Output:
nodalo
Explanation:
If the string to be copied has more than 10 letters, strcpy cannot copy this string
into the string 'myname'. This is because string 'myname' is declared to be of
size 10 characters only.
In the above program, string "nodalo" is copied in myname and is printed on
output screen.
strdup function: duplicates a string to a location that will be decided by the
function itself. Function will copy the contents of string to certain memory
location and returns the address to that location. 'strdup' sounds like short form
of "string duplicate"
Syntax:
strdup (const char *s);
strdup returns a pointer to a character or base address of an array. Function
returns address of the memory location where the string has been copied. In
case free space could not be created then it returns a null pointer. Both strcpy
and strdup functions are present in header file
Program: Program to illustrate strdup().
#include
#include
#include
int main(void) {
char myname[] = "nodalo";
//name is pointer variable which
//can store the address of
//memory location of string
char* name;
//contents of myname are copied
//in a memory address
//and are assigned to name
name = strdup(myname);
//prints the contents of 'name'
puts(name);
//prints the contents of 'myname'
puts(myname);
//memory allocated to 'name'
//is now freed
free(name);
return 0;
}
Output:
nodalo
nodalo
Explanation:
string myname consists of "nodalo" stored in it. Contents of myname are copied
in a memory address and memory is assigned to name. At the end of the
program, memory can be freed using free(name);

48. What is difference between for loop and while loop in C language?
for loop: When it is desired to do initialization, condition check and increment/
decrement in a single statement of an iterative loop, it is recommended to use
'for' loop.
Syntax:
for(initialisation;condition;increment/decrement)
{
//block of statements
increment or decrement
}
Program: Program to illustrate for loop
#include
int main() {
int i;
for (i = 1; i <= 5; i++) {
//print the number
printf("\n %d", i);
}
return 0;
}
1
2
3
4
5
Output:
Explanation:
The loop repeats for 5 times and prints value of 'i' each time. 'i' increases by 1 for
every cycle of loop.
while loop: When it is not necessary to do initialization, condition check and
increment/decrement in a single statement of an iterative loop, while loop could
be used. In while loop statement, only condition statement is present.
Syntax:
while(expression/condition)
{
//block of statements
increment or decrement
}
Program: Program to illustrate while loop.
#include
int main() {
int i = 0, flag = 0;
int a[10] = { 0, 1, 4, 6, 89, 54, 78, 25, 635, 500 };
//This loop is repeated until
//the condition is false.
while (flag == 0) {
if (a[i] == 54) {
//as element is found, flag = 1
//Hence loop terminates
flag = 1;
} else {
i++;
}
}
printf("Element found at %d th location", i);
return 0;
}
Output:
Element found at 5th location
Explanation:
Here flag is initialised to zero. 'while' loop repeats until the value of flag is zero,
increments i by 1. 'if' condition checks whether number 54 is found. If found,
value of flag is set to 1 and 'while' loop terminates.

49. Write down the equivalent pointer expression for referring the same
element as a[i][j][k][l]. Explain.
Consider a multidimensional array a[w][x][y][z].
In this array, a[i] gives address of a[i][0][0][0] and a[i]+j gives the address of
a[i][j][0][0]
Similarly, a[i][j] gives address of a[i][j][0][0] and a[i][j]+k gives the address of
a[i][j][k][0]
a[i][j][k] gives address of a[i][j][k][0] and a[i][j][k]+l gives address of a[i][j][k][l]
Hence a[i][j][k][l] can be accessed using pointers as *(a[i][j][k]+l)
where * stands for value at address and a[i][j][k]+l gives the address location of
a[i][j][k][l].
Program: Example program to illustrate pointer denotation of multi-dimensional
arrays.
#include
#include
int main() {
int a[3][3][3][3];
//it gives address of a[0][0][0][0] .
printf(" \n address of array a is %u", a);
printf("\n address of a[2][0][0][0] is %u , "
"given by a[2] , %u given by a+2",
a[2], a + 2);
printf("\n address of a[2][2][0][0] is %u , "
"given by a[2][2] , %u given by a[2]+2",
a[2][2], a[2] + 2);
printf("\n address of a[2][2][1][0] is %u , "
"given by a[2][2][1] , %u given by a[2][2]+1",
a[2][2][1], a[2][2] + 1);
return 0;
}
Output:
address of array a is 65340
address of a[2][0][0][0] is 65448, given by a[2] , 65448 given by a+2
address of a[2][2][0][0] is 65484, given by a[2][2] ,65484 given by a[2]+2
address of a[2][2][1][0] is 65490, given by a[2][2][1] , 65490 given by a[2][2]+1
Explanation:
This output may differ from computer to computer as the address locations are
not same for every computer.

50. Which one is equivalent to multiplying an unsigned int by 2, left shifting by
1 or right shifting by 1?
Left shifting of an unsigned integer is equivalent to multiplying an unsigned int by
2.
Eg1: 14<<1;
consider a number 14-----00001110 (8+4+2)is its binary equivalent
left shift it by 1--------------00011100(16+8+4) which is 28.
Eg2: 1<<1;
consider the number as 1---00000001(0+0+1).
left shift that by 1------------00000010(0+2+0) which is 2.
left shift by 1 bit of a number=2*number
left shift by 1 bit of 2*number=2*2*number
left shift by n bits of number=(2^n)*number
Program: Program to illustrate left shift and right shift operations.
#include
int main(void)
{
 int x=10,y=10;
printf("left shift of 10 is %d \n",x<<1);
printf("right shift of 10 is: %d \n",y>>1);
return 0;
}
Output:
left shift of 10 is 20
right shift of 10 is: 5
press any key to continue . . .
Explanation:
Left shift (by 1 position) multiplies a number by two. Right shift divides a number
by 2.