CHAPTER 1: Variables & Control Flow

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1)What is C language?

DRex Electronics

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.

2)What is the difference between declaring a variable and defining a variable?

Declaration of a variable in C hints the compiler about the type and size of the variable in compile time. Similarly, declaration of a function hints about type and size of function parameters. No space is reserved in memory for any variable in case of declaration.

Example: int a;
Here variable ‘a’ is declared of data type ‘int’
Defining a variable means declaring it and also allocating space to hold it. We can say “Definition = Declaration + Space reservation”.

Example: int a = 10;
Here variable “a” is described as an int to the compiler and memory is allocated to hold value 10.

3)What is a static variable?

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 initialized by using keyword static before variable name.

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 initialized only once no matter how many times that function in which it resides is called.

It may be used as a count variable.

#include <stdio.h> //program in file f1.c
void count(void)
{
static int count1 = 0;
count1++; count2++;
int count2 = 0;
printf(“\nValue of count1 is %d, Value of count2 is %d”, count1, count2); }
/*Main function*/ int main(){ count(); count(); count();
return 0;
}

Output:

Value of count1 is 1, Value of count2 is 1 Value of count1 is 2, Value of count2 is 1

4)What is a register variable?

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.

5)Where is an 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.

6) What is scope & storage allocation of extern and global variables?

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:
/*************** Index: f1.c
****************/
#include <stdio.h> extern int x;

int main() {
printf(“value of x %d”, x); return 0; }

Index: 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 <stdio.h> 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);
}
int main(){
printf(“\n value of x: %d”, x); increment();
return 0;
}

7) What is scope & storage allocation of register, static and local variables?

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.

#include <stdio.h> void decrement(){

static int a=5; a–;
printf(“Value of a:%d\n”, a); }
int main(){ decrement(); return 0;

}

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.

8)What are storage memory, default value, scope and life of Automatic and Register storage class?

a) Automatic storage class:

Storage : Default : value

Scope :

main memory. garbage value.
local to the block in which the variable is defined.

Lifetime : till control remains within the block.

b) Register storage class:

Storage : Default value : Scope : Lifetime :

CPU registers.
garbage value.
local to the block in which the variable is defined. till control remains within the block.

9) What are storage memory, default value scope and life of Static and External storage class?

1. Static storage class:

Storage : main memory.
Default : zero
value
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 : zero
value
Scope : global

Lifetime : as long as the program execution doesn’t come to an end.

10. What is the difference between ‘break’ and ‘continue’ statements? Differences between ‘break’ and ‘continue’ statements

break

1. break is a keyword used to terminate the loop or exit from the block. The control jumps to next statement after the loop or block.

2.Syntax:

{ Statement 1; Statement 2; Statement n; break;

}
{ Statement 1; continue;
Statement 2;
}

3. break can be used with for, while, do- while, and switch statements. When break is used in nested loops i.e. within the inner most loop then only the innermost loop is terminated.

4. Example:

3. This statement when occurs in a loop does not terminate it but skips the statements after this continue statement. The control goes to the next iteration. continue can be used with for, while and do-while.

4. Example:

i = 1, j = 0; while(i<=5) {
i = 1, j = 0; while(i<=5) {

i=i+1;
if(i== 2) break; j=j+1;
}

continue

1. continue is a keyword used for skipping the current iteration and go to next iteration of the loop

2.Syntax:

i=i+1;
if(i== 2) continue; j=j+1;
}

11)printf() Function What is the output of printf(“%d”)?

1. When we write printf(“%d”,x); this means compiler will print the value of x. But as here, there is nothing after %d so compiler will show in output window garbage value.

2. When we use %d the compiler internally uses it to access the argument in the stack (argument stack). Ideally compiler determines the offset of the data variable depending on the format specification string. Now when we write printf(“%d”,a) then compiler first accesses the top most element in the argument stack of the printf which is %d and depending on the format string it calculated to offset to the actual data variable in the memory which is to be printed. Now when only %d will be present in the printf then compiler will calculate the correct offset (which will be the offset to access the integer variable) but as the actual data object is to be printed is not present at that memory location so it will print what ever will be the contents of that memory location.

3. Some compilers check the format string and will generate an error without the proper number and type of arguments for things like printf(…) and scanf(…).

12)What is the difference between ‘for’ and ‘while’ loops?

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(initialization;condition;increment/decrement) {
//block of statements increment or decrement

}

Program: Program to illustrate for loop

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

int i;
for (i = 1; i <= 5; i++) { //print the number printf(“\n %d”, i); }
return 0;
}

Output:

1
2
3
4
5

Explanation: The loop repeats for 5 times and prints value of ‘i’ each time. ‘i’ increases by 1 for every cycle of loop

CHAPTER 2 :Operators, Constants & Structures

13. 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.

14. Which bitwise 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));
1 can be represented in binary as 0b00000001 = (1<<4) << is a left bit shift operator,
it shifts 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.

15. What is equivalent of multiplying an unsigned int by 2: left shift of number by 1 or right shift of number 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<stdio.h>
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

Explanation:

Left shift (by 1 position) multiplies a number by two. Right shift divides a number by 2.

16. What is an Enumeration Constant?

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;

17. 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 accesing name field of student2 object.

18. What are the differences between a structure and a union?

Structures and Unions are used to store members of different data types.

STRUCTURE

a) Declaration: UNION
a)Declaration:

struct {
union

{
data type member1; data type

member2; };

data type member1; data type member2; };

b)Every structure member is allocated memory when a structure variable is defined.
Example:

b)The memory equivalent to the largest item is allocated commonly for all members.
Example:

struct emp {
char name[5]; int age;
float

sal; };
struct emp e1;

union emp1 {
char name[5]; int age;
float

sal; };
union emp1 e2;

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 Memory allocated to a union is equal to size of the largest member. In this case, float is the largestsized data type. Hence memory allocated to this union is 4 bytes.

c)Only one union member can be initialized at a time

struct st { int a;
float b; };

struct st s = { .a=4, .b=10.5 }; union un
{ int a;
float b;

};
union un un1 = { .a=10 };

Structure is used when all members are to be independently used in a program. Union is used when members of it are not required to be accessed at the same time.

19. What are the advantages of 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.

20. How can typedef be to define a type of structure?

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;

21. Write a program that returns 3 numbers from a function using a structure.

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.

Program: Program with a function to return 3 values

#include<stdio.h>
//sample structure which has three integer
variables. struct sample {
int a, b,
c; };
//this is function which returns three
values. struct sample return3val() {

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() {
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); return 0;

}

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.

22. In code snippet below:

struct Date {
int yr;
int day;
int month;

} date1,date2; d

ate1.yr = 2004;
date1.day = 4;
date1.month = 12;

Write a function that assigns values to date2. Arguments to the function must be pointers to the structure, Date and integer variables date, month, year.

Date is a 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<stdio.h>
#include<stdlib.h>
//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.yr); printf(“\n %d %d %d date2.month, date2.yr); return 0;

}

Output:
4 12 2004
5 12 2008

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.
date1.month,

“, date2.day,

CHAPTER 3: Functions

23. What is the purpose of main() function?

In C, program execution starts from the main() function. Every C program must contain a main() function. The main function may contain any number of statements. These statements are executed sequentially in the order which they are written.

The main function can in-turn call other functions. When main calls a function, it passes the execution control to that function. The function returns control to main when a return statement is executed or when end of function is reached.

In C, the function prototype of the ‘main’ is one of the following:

int main(); //main with no arguments
int main(int argc, char *argv[]); //main with arguments

The parameters argc and argv respectively give the number and value of the program’s commandline arguments.

Example:

#include <stdio.h>
/* program section begins here
*/ int main() {
// opening brace – program execution starts

here printf(“Welcome to the world of C”); return 0;
}
// closing brace – program terminates here

Output:

Welcome to the world of C

24. Explain command line arguments of main function?

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 <stdio.h>
int 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\n”, argc); return 0;

}

Output:

Following are the arguments entered in the command
line C:\testproject.exe
apple
mango
Number of arguments entered
are 3

25. 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<some.h> 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<stdio.h> //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.

Program: Custom header files example /****************

Index: restaurant.h
****************/
int billAll(int food_cost, int tax, int tip);

/****************
Index: restaurant.c
****************/
#include<stdio.h>
int billAll(int food_cost, int tax, int tip)
{ int result;
result = food_cost + tax + tip; printf(“Total bill is
%d\n”,result); return result;

/****************
Index: main.c
****************/
#include<stdio.h>
#include”restaurant.h” int main() {

int food_cost, tax,
tip; food_cost = 50; tax = 10;
tip = 5;
billAll(food_cost,tax,tip); return 0;

 

}

26. What are the differences between formal arguments and actual arguments of a function?

Argument: An argument is an expression which is passed to a function by its caller (or macro by its invoker) in order for the function(or macro) to perform its task. It is an expression in the comma-separated list bound by the parentheses in a function call expression.

Actual arguments:

The arguments that are passed in a function call are called actual arguments. These arguments are defined in the calling function.

Formal arguments:

The formal arguments are the parameters/arguments in a function declaration. The scope of formal arguments is local to the function definition in which they are used. Formal arguments belong to the called function. Formal arguments are a copy of the actual arguments. A change in formal arguments would not be reflected in the actual arguments.

Example:

#include <stdio.h>
void sum(int i, int j, int
k); /* calling function */
int main() {

int a = 5;
// actual
arguments sum(3,
2 * a, a); return 0;

}

/* called function */ /* formal arguments*/
void sum(int i, int j, int k)

{ int s;
s = i + j + k;
printf(“sum is %d”, s);

}

Here 3,2*a,a are actual arguments and i,j,k are formal arguments.

27. What is pass by value in functions?

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 <stdio.h>
void swap(int x, int y)
{ int t;

t = x;
x = y;
y = t;

}
int main() {
int m = 10, n = 20;
printf(“Before executing swap m=%d n=%d\n”, m, n); swap(m, n);
printf(“After executing swap m=%d n=%d\n”, m, n); return 0;

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.

28. What is pass by reference in functions?

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. C does not support Call by reference. But it can be simulated using pointers.

Example:

#include <stdio.h>
/* 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 */

}
int main() {
int m = 10, n = 20;
printf(“Before executing swap m=%d n=%d\n”, m, n); swap(&m, &n);
printf(“After executing swap m=%d n=%d\n”, m, n); return 0;

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.

29. What are the differences between getchar() and scanf() functions for reading strings?

Differences between getchar and scanf functions for reading strings:

scanf
1. Entering of each character should be followed, by return key.

2. Continuous stream of characters cannot be directly supplied using scanf function.

3. Scanf function can be used to provide data at execution time irrespective of its type(int, char, float).

Example:

#include<stdio.h> int main() {
char a[10];
printf(“Enter a: \n”);
scanf(“%s”,a);
return 0;
}

getchar

1. Need not type return key.

2. Continuous stream of characters can be directly supplied using getchar function
3. getchar() function is used only with character type.

Example:

#include<stdio.h>
int main() {
char a;
printf(“Enter any character: \n”); a = getchar();
printf(“Character entered:%c \n”,a); return 0;

}

4. scanf() returns the number of items read successfully. A return value 0 indicates that no fields were read. EOF(end of file) is returned in case of an error or if end-of-file/end-of-string character is encountered.

5. getchar() returns the character entered as the value of the function. It returns EOF in case of an error. It is recommeded to use getchar instead of scanf.

30. Out of the functions fgets() and gets(), which one 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( ).

31. What is the difference between the functions strdup() and strcpy()?

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.

Example Program:

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

char myname[10];
//copy contents to myname
strcpy(myname,
“interviewmantra.net”); //print the string puts(myname);
return 0;

}

Output:

interviewmantra.net

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 <string.h>

Program: Program to illustrate strdup().

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

char myname[] = “interviewmantra.net”; //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:

interviewmantra.net interviewmantra.net

Explanation:

String myname consists of “interviewmantra.net” 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);

CHAPTER 4: Pointers

32. What is a pointer in C?

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.

ap=ap+1;

Above expression would not increment the value of ap by one, 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.

33. What are the advantages of using pointers?

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:

1. 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.
2. Dynamic allocation of memory is possible with the help of pointers.
3. 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.
4. Pointers point to physical memory and allow quicker access to data.

34. 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.

35. How to use realloc() to dynamically increase size of an already 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.

36. What is the equivalent pointer expression for referring an element a[i][j][k][l], in a four dimensional array?

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<stdio.h>
#include<string.h>
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.

37. Declare an array of three function pointers where each function receives two integers and returns float.

Declaration:

float (*fn[3])(int, int); Program: Illustrates the usage of above declaration

#include<stdio.h>
float (*fn[3])(int, int);
float add(int, int); int
main() {

int x, y, z, j;
for (j = 0; j < 3; j++){
fn[j] = &add;
}
x = fn[0](10, 20);
y = fn[1](100, 200);
z = fn[2](1000, 2000);
printf(“sum1 is: %d \n”,
x); printf(“sum2 is: %d
\n”, y); printf(“sum3 is:
%d \n”, z); return 0;

}
float add(int x, int y)
{ float f = x + y;
return f;

}

Output: sum1 is: 30 sum2 is: 300 sum3 is: 3000

Explanation:

Here ‘fn[3]’ is an array of function pointers. Each element of the array can store the address of function ‘float add(int, int)’.

fn[0]=fn[1]=fn[2]=&add

Wherever this address is encountered add(int, int) function is called.

38. 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.

return type : integer pointer.
p[10] : array of function pointers
char * : arguments passed to the function

Program: Example program to explain function pointers.

#include<stdio.h>
#include<stdlib.h>
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] = &(sum);
}
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]);

}
}
return 0;

}
//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

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.

39. What is the value of

sizeof(a) /sizeof(char *)
in a code snippet:
char *a[4]={“sridhar”,”raghava”,”shashi”,”srikanth”};

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.

40. (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. 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 can not 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’.

CHAPTER 5: Some Similar Question in Diff way

41. malloc() Function- What is the difference between “calloc(…)” and “malloc(…)”?

1. calloc(…) allocates a block of memory for an array of elements of a certain size. By default the block is initialized to 0. The total number of memory allocated will be (number_of_elements * size).

malloc(…) takes in only a single argument which is the memory required in bytes. malloc(…) allocated bytes of memory and not blocks of memory like calloc(…).

2. malloc(…) allocates memory blocks and returns a void pointer to the allocated space, or NULL if there is insufficient memory available.

calloc(…) allocates an array in memory with elements initialized to 0 and returns a pointer to the allocated space. calloc(…) calls malloc(…) in order to use the C++ _set_new_mode function to set the new handler mode.

42. printf() Function- What is the difference between “printf(…)” and “sprintf(…)”?

sprintf(…) writes data to the character array whereas printf(…) writes data to the standard output device.

Compilation How to reduce a final size of executable?

Size of the final executable can be reduced using dynamic linking for libraries.

43. Linked Lists — Can you tell me how to check whether a linked list is circular?

Create two pointers, and set both to the start of the list. Update each as follows:
while (pointer1) { pointer1 = pointer1->next; pointer2 = pointer2->next;
if (pointer2) pointer2=pointer2->next; if (pointer1 == pointer2) {
print (“circular”);
}
}
If a list is circular, at some point pointer2 will wrap around and be either at the item just before pointer1, or the item before that. Either way, its either 1 or 2 jumps until they meet.

44. “union” Data Type What is the output of the following program? Why?

#include main() { typedef union { int a;
char b[10]; float c;
}
Union;
Union x,y = {100}; x.a = 50; strcpy(x.b,”hello”); x.c = 21.50;
printf(“Union x : %d %s %f n”,x.a,x.b,x.c); printf(“Union y : %d %s %f n”,y.a,y.b,y.c);
}

45. What does static variable mean?

there are 3 main uses for the static.

1. If you declare within a function:
It retains the value between function calls

2.If it is declared for a function name:
By default function is extern..so it will be visible from other files if the function declaration is as static..it is invisible for the outer files

3. Static for global variables:
By default we can use the global variables from outside files If it is static global..that variable is limited to with in the file

46. Advantages of a macro over a function?

Macro gets to see the Compilation environment, so it can expand __ __TIME____ #defines. It is expanded by the preprocessor.

For example, you can’t do this without macros #define PRINT(EXPR) printf( #EXPR “=%d\n”, EXPR

) PRINT( 5+6*7 ) // expands into printf(”5+6*7=%d”, 5+6*7 );
You can define your mini language with macros: #define strequal(A,B) (!strcmp(A,B))

Macros are a necessary evils of life. The purists don’t like them, but without it no real work gets done.

47. What are the differences between malloc() and calloc()?

There are 2 differences. First, is in the number of arguments. malloc() takes a single argument(memory required in bytes), while calloc() needs 2 arguments(number of variables to allocate memory, size in bytes of a single variable).

Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO.

48. What are the different storage classes in C?

C has three types of storage: automatic, static and allocated.

Variable having block scope and without static specifier have automatic storage duration.

Variables with block scope, and with static specifier have static scope. Global variables (i.e, file scope) with or without the static specifier also have static scope.

Memory obtained from calls to malloc(), alloc() or realloc() belongs to allocated storage class.

49. What is the difference between strings and character arrays?

A major difference is: string will have static storage duration, whereas as a character array will not, unless it is explicity specified by using the static keyword.

Actually, a string is a character array with following properties:

the multibyte character sequence, to which we generally call string, is used to initialize an array of static storage duration. The size of this array is just sufficient to contain these characters plus the terminating NUL character.

it not specified what happens if this array, i.e., string, is modified.

Two strings of same value[1] may share same memory area. For example, in the following declarations:

char *s1 = “Calvin and Hobbes”; char *s2 = “Calvin and Hobbes”;

the strings pointed by s1 and s2 may reside in the same memory location. But, it is not true for the following:

char ca1[] = “Calvin and Hobbes”; char ca2[] = “Calvin and Hobbes”;

[1] The value of a string is the sequence of the values of the contained characters, in order.

50. Difference between const char* p and char const* p

In const char* p, the character pointed by ‘p’ is constant, so u cant change the value of character pointed by p but u can make ‘p’ refer to some other location.

In char const* p, the ptr ‘p’ is constant not the character referenced by it, so u cant make ‘p’ to reference to any other location but u can change the value of the char pointed by ‘p’.

51. What is hashing?

To hash means to grind up, and that’s essentially what hashing is all about. The heart of a hashing algorithm is a hash function that takes your nice, neat data and grinds it into some random-looking integer.

The idea behind hashing is that some data either has no inherent ordering (such as images) or is expensive to compare (such as images). If the data has no inherent ordering, you can’t perform comparison searches.

If the data is expensive to compare, the number of comparisons used even by a binary search might be too many. So instead of looking at the data themselves, you’ll condense (hash) the data to an integer (its hash value) and keep all the data with the same hash value in the same place. This task is carried out by using the hash value as an index into an array.

To search for an item, you simply hash it and look at all the data whose hash values match that of the data you’re looking for. This technique greatly lessens the number of items you have to look at. If the parameters are set up with care and enough storage is available for the hash table, the number of comparisons needed to find an item can be made arbitrarily close to one.

One aspect that affects the efficiency of a hashing implementation is the hash function itself. It should ideally distribute data randomly throughout the entire hash table, to reduce the likelihood of collisions. Collisions occur when two different keys have the same hash value.

There are two ways to resolve this problem. In open addressing, the collision is resolved by the choosing of another position in the hash table for the element inserted later. When the hash table is searched, if the entry is not found at its hashed position in the table, the search continues checking until either the element is found or an empty position in the table is found.

The second method of resolving a hash collision is called chaining. In this method, a bucket or linked list holds all the elements whose keys hash to the same value. When the hash table is searched, the list must be searched linearly.

52. How can you determine the size of an allocated portion of memory?

You can’t, really. free() can , but there’s no way for your pr ogram to know the trick free() uses. Even if you disassemble the library and discover the trick, there’s no guarantee the trick won’t change with the next release of the compiler.

53. Can static variables be declared in a header file?

You can’ t declare a static variable without defining it as well (this is because the storage class modifiers static and extern are mutually exclusive). A static variable can be defined in a header file, but this would cause each source file that included the header file to have its own private copy of the variable, which is probably not what was intended.

54. Can a variable be both const and volatile?

Yes. The const modifier means that this code cannot change the value of the variable, but that does not mean that the value cannot be changed by means outside this code. For instance, in the example in FAQ 8, the timer structure was accessed through a volatile const pointer. The function itself did not change the value of the timer, so it was declared const. However, the value was changed by hardware on the computer, so it was declared volatile. If a variable is both const and volatile, the two modifiers can appear in either order.

55. Can include files be nested?

Yes. Include files can be nested any number of times. As long as you use precautionary measures , you can avoid including the same file twice. In the past, nesting header files was seen as bad programming practice, because it complicates the dependency tracking function of the MAKE program and thus slows down compilation. Many of today’s popular compilers make up for this difficulty by implementing a concept called precompiled headers, in which all headers and associated dependencies are stored in a precompiled state.

Many programmers like to create a custom header file that has #include statements for every header needed for each module. This is perfectly acceptable and can help avoid potential problems relating to #include files, such as accidentally omitting an #include file in a module.

56. When does the compiler not implicitly generate the address of the first element of an array?

Whenever an array name appears in an expression such as • array as an operand of the sizeof operator
• array as an operand of & operator
• array as a string literal initializer for a character array
• Then the compiler does not implicitly generate the address of the address of the first element of an array.

57. What is a null pointer?

There are times when it’s necessary to have a pointer that doesn’t point to anything. The macro NULL, defined in , has a value that’s guaranteed to be different from any valid pointer. NULL is a literal zero, possibly cast to void* or char*. Some people, notably C++ programmers, prefer to use 0 rather than NULL.

The null pointer is used in three ways:
1) To stop indirection in a recursive data structure
2) As an error value
3) As a sentinel value

58. What is the difference between text and binary modes?

Streams can be classified into two types: text streams and binary streams. Text streams are interpreted, with a maximum length of 255 characters. With text streams, carriage return/line feed combinations are translated to the newline n character and vice versa. Binary streams are uninterrupted and are treated one byte at a time with no translation of characters. Typically, a text stream would be used for reading and writing standard text files, printing output to the screen or printer, or receiving input from the keyboard.

A binary text stream would typically be used for reading and writing binary files such as graphics or word processing documents, reading mouse input, or reading and writing to the modem.

59. What is static memory allocation and dynamic memory allocation?

Static memory allocation: The compiler allocates the required memory space for a declared variable.By using the address of operator,the reserved address is obtained and this address may be assigned to a pointer variable.Since most of the declared variable have static memory,this way of assigning pointer value to a pointer variable is known as static memory allocation. memory is assigned during compilation time.

Dynamic memory allocation: It uses functions such as malloc( ) or calloc( ) to get memory dynamically.If these functions are used to get memory dynamically and the values returned by these functions are assingned to pointer variables, such assignments are known as dynamic memory allocation.memory is assined during run time.

60. When should a far pointer be used?

Sometimes you can get away with using a small memory model in most of a given program. There might be just a few things that don’t fit in your small data and code segments. When that happens, you can use explicit far pointers and function declarations to get at the rest of memory. A far function can be outside the 64KB segment most functions are shoehorned into for a small-code model. (Often, libraries are declared explicitly far, so they’ll work no matter what code model the program uses.) A far pointer can refer to information outside the 64KB data segment. Typically, such pointers are used with farmalloc() and such, to manage a heap separate from where all the rest of the data lives. If you use a small- data, large-code model, you should explicitly make your function pointers far.

61. How are pointer variables initialized?

Pointer variable are initialized by one of the following two ways
• Static memory allocation
• Dynamic memory allocation

62. Difference between arrays and pointers?

– Pointers are used to manipulate data using the address. Pointers use * operator to access the data pointed to by them
– Arrays use subscripted variables to access and manipulate data. Array variables can be equivalently written using pointer expression.

63. Is using exit() the same as using return?

No. The exit() function is used to exit your program and return control to the operating system. The return statement is used to return from a function and return control to the calling function. If you issue a return from the main() function, you are essentially returning control to the calling function, which is the operating system. In this case, the return statement and exit() function are similar.

64. What is a method?

Method is a way of doing something, especially a systematic way; implies an orderly logical arrangement (usually in steps).

65. What is indirection?

If you declare a variable, its name is a direct reference to its value. If you have a pointer to a variable, or any other object in memory, you have an indirect reference to its value.

66. What is modular programming? 

If a program is large, it is subdivided into a number of smaller programs that are called modules or subprograms. If a complex problem is solved using more modules, this approach is known as modular programming.

67. How many levels deep can include files be nested? 

Even though there is no limit to the number of levels of nested include files you can have, your compiler might run out of stack space while trying to include an inordinately high number of files. This number varies according to your hardware configuration and possibly your compiler.

68. What is the difference between declaring a variable and defining a variable? 

Declaring a variable means describing its type to the compiler but not allocating any space for it. Defining a variable means declaring it and also allocating space to hold the variable. You can also initialize a variable at the time it is defined.

69. What is an lvalue?

An lvalue is an expression to which a value can be assigned. The lvalue expression is located on the left side of an assignment statement, whereas an rvalue is located on the right side of an assignment statement. Each assignment statement must have an lvalue and an rvalue. The lvalue expression must reference a storable variable in memory. It cannot be a constant.

70. Differentiate between an internal static and external static variable?

An internal static variable is declared inside a block with static storage class whereas an external static variable is declared outside all the blocks in a file.An internal static variable has persistent storage,block scope and no linkage.An external static variable has permanent storage,file scope and internal linkage.

71. What is the difference between a string and an array?

An array is an array of anything. A string is a specific kind of an array with a well-known convention to determine its length.

There are two kinds of programming languages: those in which a string is just an array of characters, and those in which it’s a special type. In C, a string is just an array of characters (type char), with one wrinkle: a C string always ends with a NUL character.

The “value” of an array is the same as the address of (or a pointer to) the first element; so, frequently, a C string and a pointer to char are used to mean the same thing.

An array can be any length. If it’s passed to a function, there’s no way the function can tell how long the array is supposed to be, unless some convention is used. The convention for strings isNUL termination; the last character is an ASCII NUL (‘’) character.

72. What is an argument? Differentiate between formal arguments and actual arguments?

An argument is an entity used to pass the data from calling function to the called function. Formal arguments are the arguments available in the function definition. They are preceded by their own data types. Actual arguments are available in the function call.

73. What are advantages and disadvantages of external storage class?

Advantages of external storage class

1)Persistent storage of a variable retains the latest value
2)The value is globally available

Disadvantages of external storage class

1)The storage for an external variable exists even when the variable is not needed
2)The side effect may produce surprising output
3)Modification of the program is difficult
4)Generality of a programis affected

74. What is a void pointer?

A void pointer is a C convention for a raw address. The compiler has no
idea what type of object a void Pointer really points to. If you write int *ip;
ip points to an int. If you write
void *p;
p doesn’t point to a void!

In C and C++, any time you need a void pointer, you can use another pointer type. For example, if you have a char*, you can pass it to a function that expects a void*. You don’t even need to cast it. In C (but not in C++), you can use a void* any time you need any kind of pointer, without casting. (In C++, you need to cast it).

A void pointer is used for working with raw memory or for passing a pointer to an unspecified type.

Some C code operates on raw memory. When C was first invented, character pointers (char *) were used for that. Then people started getting confused about when a character pointer was a string, when it was a character array, and when it was raw memory.

75. When should a type cast not be used?

A type cast should not be used to override a const or volatile declaration. Overriding these type modifiers can cause the program to fail to run correctly.

A type cast should not be used to turn a pointer to one type of structure or data type into another. In the rare events in which this action is beneficial, using a union to hold the values makes the programmer’s intentions clearer.

76. When is a switch statement better than multiple if statements?

A switch statement is generally best to use when you have more than two conditional expressions based on a single variable of numeric type.

77. What is a static function?

A static function is a function whose scope is limited to the current source file. Scope refers to the visibility of a function or variable. If the function or variable is visible outside of the current source file, it is said to have global, or external, scope. If the function or variable is not visible outside of the current source file, it is said to have local, or static, scope.

78. What is a pointer variable?

A pointer variable is a variable that may contain the address of another variable or any valid address in the memory.

79. What is a pointer value and address?

A pointer value is a data object that refers to a memory location. Each memory location is numbered in the memory. The number attached to a memory location is called the address of the location.

80. What is a modulus operator? What are the restrictions of a modulus operator?

A Modulus operator gives the remainder value. The result of x%y is obtained by (x-(x/y)*y). This operator is applied only to integral operands and cannot be applied to float or double.

81. Differentiate between a linker and linkage?

A linker converts an object code into an executable code by linking together the necessary build in functions. The form and place of declaration where the variable is declared in a program determine the linkage of variable.

82. What is a function and built-in function?

A large program is subdivided into a number of smaller programs or subprograms. Each subprogram specifies one or more actions to be performed for a large program. such subprograms are functions.

The function supports only static and extern storage classes. By default, function assumes extern storage class. functions have global scope. Only register or auto storage class is allowed in the function parameters. Built-in functions that predefined and supplied along with the compiler are known as built-in functions. They are also known as library functions.

83. Why should I prototype a function?

A function prototype tells the compiler what kind of arguments a function is looking to receive and what kind of return value a function is going to give back. This approach helps the compiler ensure that calls to a function are made correctly and that no erroneous type conversions are taking place.

84. What is Polymorphism ?

‘Polymorphism’ is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form. Polymorphism leads to two important aspects in Object Oriented terminology – Function Overloading and Function Overriding. Overloading is the practice of supplying more than one definition for a given function name in the same scope. The compiler is left to pick the appropriate version of the function or operator based on the arguments with which it is called. Overriding refers to the modifications made in the sub class to the inherited methods from the base class to change their behavior.

85. What is Operator overloading ?

When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings. Examples:

1) The operators >> and << may be used for I/O operations because in the header, they are overloaded.
2) In a stack class it is possible to overload the + operator so that it appends the contents of one stack to the contents of another. But the + operator still retains its original meaning relative to other types of data.

86. What is the difference between goto and longjmp() and setjmp()?

3) A goto statement implements a local jump of program execution, and the longjmp() and setjmp() functions implement a nonlocal, or far,
jump of program execution.

Generally, a jump in execution of any kind should be avoided because it is not considered good programming practice to use such statements as goto and longjmp in your program.

A goto statement simply bypasses code in your program and jumps to a predefined position. To use the goto statement, you give it a labeled position to jump to. This predefined position must be within the same function. You cannot implement gotos between functions.

When your program calls setjmp(), the current state of your program is saved in a structure of type jmp_buf. Later, your program can call the longjmp() function to restore the program’s state as it was when you called setjmp().Unlike the goto statement, the longjmp() and setjmp() functions do not need to be implemented in the same function.

However, there is a major drawback to using these functions: your program, when restored to its previously saved state, will lose its references to any dynamically allocated memory between the longjmp() and the setjmp(). This means you will waste memory for every malloc() or calloc() you have implemented between your longjmp() and setjmp(), and your program will be horribly inefficient.

It is highly recommended that you avoid using functions such as longjmp() and setjmp() because they, like the goto statement, are quite often an indication of poor programming practice.

CHAPTER 6: Programs

87. . Write a program to find factorial of the given number.

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 <stdio.h>
int fact(int n);
int 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);
return 0;

}
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.

88. . Write a program to check whether the given number is even or odd.

Program:

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

int a;
printf(“Enter a: \n”);
scanf(“%d”, &a);
/* logic */
if (a % 2 == 0) {
printf(“The given number is EVEN\n”);
}
else {
printf(“The given number is ODD\n”);
}
return 0;

}

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.

89. . 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 <stdio.h>

int 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);
return 0;

}

Output:
Enter the values of a and b: 2 3 Before swapping a=2, b=3 After swapping a=3, b=2

90. 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 <stdio.h>

int main() {
int a, b;
printf(“Enter values of a and b:\n”);
scanf(“%d %d”, &a, &b);
printf(“Before swapping a=%d, b=%d\n”, a,b); /*Swapping logic */
a = a + b;
b = a – b;
a = a – b;
printf(“After swapping a=%d b=%d\n”, a, b);
return 0;

}

Output:
Enter values of a and b: 2 3
Before swapping a=2, b=3
The values after swapping are a=3 b=2

91. Write a program to swap two numbers using bitwise operators.

Program:

#include <stdio.h>
int 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);
return 0;

}

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)

92. Write a program to find the greatest of three numbers.

Program:

#include <stdio.h>
int 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”);
}
return 0;

}

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 checking this condition for 5,4,8 i.e.
else if(8>5 && 8>4) /* both conditions are satisfied */

now the control shifts to the next else if condition else if(c>a && c>b) then c is greater than a and b
Thus c is greater than a and b.

93. Write a program to find the greatest among ten numbers.

Program:

#include <stdio.h>
int 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);
return 0;

}

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.

94. Write a program to check whether the given number is a prime.

A prime number is a natural number that has only one and itself as factors. Examples: 2, 3, 13 are prime numbers.

Program:

#include
<stdio.h> 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”);
}
return 0;
}

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 until the n value equals i */ i.e. for(i=0;i<=5;i++) /* here the for loop is executed until 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.

95. Write a program to check whether the 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 <stdio.h>
int 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”);
}
return 0;

}

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.

96.Write a program to check whether the 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 <stdio.h>
#include <string.h>
int main() {

char string1[20];
int i, length;
int flag = 0;
printf(“Enter a string:
\n”); scanf(“%s”, string1);
length = strlen(string1);
for(i=0;i < length ;i++){
if(string1[i] != string1[length-i-1]){

flag = 1;
break;
}
}
if (flag) {
printf(“%s is not a palindrome\n”, string1);
}
else {
printf(“%s is a palindrome\n”, string1);
}
return 0;
}

Output:
Enter a string: radar “radar” is a palindrome

Explanation with example:

To check if a string is a palindrome or not, a string needs to be compared with the reverse of itself.

Consider a palindrome string: “radar”, ————————–
index: 0 1 2 3 4
value: r a d a r
————————–

To compare it with the reverse of itself, the following logic is used:

0th character in the char array, string1 is same as 4th character in the same string. 1st character is same as 3rd character.
2nd character is same as 2nd character.
. . . .
ith character is same as ‘length-i-1’th character.

If any one of the above condition fails, flag is set to true(1), which implies that the string is not a palindrome. By default, the value of flag is false(0). Hence, if all the conditions are satisfied, the string is a palindrome.

97.Write a program to generate the Fibonacci series.

Fibonacci series: Any number in the series is obtained by adding the previous two numbers of the series.

Let f(n) be n’th term.
f(0)=0;
f(1)=1;
f(n)=f(n-1)+f(n-2); (for n>=2) Series is as follows
0
1
1 (1+0)
2 (1+1)
3 (1+2)
5 (2+3)
8 (3+5)
13 (5+8)
21 (8+13)
34 (13+21)
…and so on

Program: to generate Fibonacci Series(10 terms)

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

//array fib stores numbers of fibonacci
series int i, fib[25];
//initialized first element to
0 fib[0] = 0;
//initialized second element to
1 fib[1] = 1;
//loop to generate ten elements
for (i = 2; i < 10; i++) {
//i’th element of series is equal to the sum of i-1’th element and i-2’th element. fib[i] = fib[i – 1] + fib[i – 2];
}
printf(“The fibonacci series is as follows
\n”); //print all numbers in the series
for (i = 0; i < 10; i++) {

printf(“%d \n”, fib[i]);
}
return 0;

}

Output:

The fibonacci series is as follows 0 1 1 2 3 5 8 13 21 34

Explanation:

The first two elements are initialized to 0, 1 respectively. Other elements in the series are generated by looping and adding previous two numbes. These numbers are stored in an array and ten elements of the series are printed as output.

98.Write a program 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 <stdio.h>
int main() {

//printf returns the length of string being printed
if (printf(“Hello World\n”)) //prints Hello World and returns 11
{
//do nothing
}
return 0;

}

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”.

99.Write a program 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 <stdio.h>
int main(void) {

//prints the character with ascii value 59, i.e.,
semicolon if (printf(“%c\n”, 59)) {
//prints semicolon
}
return 0;

}

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(;).

100.Write a program to compare two strings without using strcmp() function.

strcmp() function compares two strings lexicographically. strcmp is declared in
stdio.h

Case 1: when the strings are equal, it returns zero.
Case 2: when the strings are unequal, it returns the difference between ascii values of the characters that differ.

a) When string1 is greater than string2, it returns positive value.
b) When string1 is lesser than string2, it returns negative value.

Syntax:

int strcmp (const char *s1, const char *s2);

Program: to compare two strings.

#include<stdio.h>
#include<string.h>
int cmpstr(char s1[10], char
s2[10]); int main() {

char arr1[10] = “Nodalo”;
char arr2[10] = “nodalo”;
printf(” %d”, cmpstr(arr1, arr2));
//cmpstr() is equivalent of
strcmp()
return 0;

}
//s1, s2 are strings to be compared int
cmpstr(char s1[10], char s2[10]) {

//strlen function returns the length of argument string passed int i = strlen(s1);
int k = strlen(s2); int bigger;

if (i < k) {
bigger = k;
}
else if (i > k) {

bigger = i;
}
else { bigger = i;
}
//loops ‘bigger’ times
for (i = 0; i < bigger; i++) {
//if ascii values of characters s1[i], s2[i] are equal do nothing if (s1[i] == s2[i]) {
}
//else return the ascii difference
else {

return (s1[i] – s2[i]);
}
}
//return 0 when both strings are same
//This statement is executed only when both strings are equal return (0); }

Output:
-32

Explanation:

cmpstr() is a function that illustrates C standard function strcmp(). Strings to be compared are sent as arguments to cmpstr(). Each character in string1 is compared to its corresponding character in string2. Once the loop encounters a differing character in the strings, it would return the ascii difference of the differing characters and exit.

101.Write a program to concatenate two strings without using strcat() function.

strcat(string1,string2) is a C standard function declared in the header file string.h The strcat() function concatenates string2, string1 and returns string1.

Program: Program to concatenate two strings

#include<stdio.h>
#include<string.h>
char *strct(char *c1, char *c2);
char *strct(char *c1, char *c2) {

//strlen function returns length of argument
string int i = strlen(c1);
int k = 0;
//loops until null is encountered and appends string c2 to
c1 while (c2[k] != ‘\0’) {
c1[i + k] =
c2[k]; k++;
}
return c1;

}

int main() {
char string1[15] = “first”;
char string2[15] =
“second”; char *finalstr;
printf(“Before concatenation:”
” \n string1 = %s \n string2 = %s”, string1, string2); //addresses of string1, string2 are passed to strct() finalstr = strct(string1, string2); printf(“\nAfter concatenation:”);
//prints the contents of string whose address is in finalstr printf(“\n finalstr = %s”, finalstr);
//prints the contents of string1
printf(“\n string1 = %s”,
string1); //prints the contents of
string2 printf(“\n string2 = %s”,
string2);
return 0;

}

Output:

Before concatenation: string1 = first
string2 = second
After concatenation: finalstr = firstsecond string1 = firstsecond string2 = second

Explanation:

string2 is appended at the end of string1 and contents of string2 are unchanged.

In strct() function, using a for loop, all the characters of string ‘c2’ are copied at the end of c1. return (c1) is equivalent to return &c1[0] and it returns the base address of ‘c1’. ‘finalstr’ stores that address returned by the function strct().

102.Write a program to delete a specified 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 <stdio.h>
int main() {

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’ scanf(“%s”, 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);
return 0;

}

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

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.

103.Write a program to replace a specified line in a text file.

Program: Program to replace a specified line in a text file.

#include <stdio.h>
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’ scanf(“%s”, filename);
fp1 = fopen(filename,
“r”); //open file in read
mode c = getc(fp1);
//print the contents of file
. while (c != EOF) {
printf(“%c”, c);
c = getc(fp1);
}
//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
original file
remove(filename);
//rename new file with old name opens the file in read mode rename(“copy.c”, filename);
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);
return 0;

}

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

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.

104.Write a program 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 <stdio.h>
int main()
/* 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’ scanf(“%s”, 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'(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);
return 0;

}

Output:

Enter file name:abc.txt There are 4 lines in abc.txt 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.

105.Write a C program which asks the user for a number between 1 to 9 and shows the number. If the user inputs a number out of the specified range, the program should show an error and prompt the user for a valid input.

Program: Program for accepting a number in a given range.

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

int input = 0;
//call a function to input number from key
board input = getnumber();
//when input is not in the range of 1 to 9,print error
message while (!((input <= 9) && (input >= 1))) {
printf(“[ERROR] The number you entered is out of range”);
//input another number
input = getnumber();
}
//this function is repeated until a valid input is given by
user. printf(“\nThe number you entered is %d”, input);
return 0;

}
//this function returns the number given by
user int getnumber() {

int number;
//asks user for a input in given range
printf(“\nEnter a number between 1 to 9
\n”); scanf(“%d”, &number);
return (number);

}

Output:

Enter a number between 1 to
9 45
[ERROR] The number you entered is out of range Enter a number between 1 to 9 4
The number you entered is 4

Explanation:
getfunction() function accepts input from user. ‘while’ loop checks whether the number falls within range or not and accordingly either prints the number(If the number falls in desired range) or shows error message(number is out of range).

106.Write a program to display the multiplication table of a given number.

Program: Multiplication table of a given number

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

int num, i = 1;
printf(“\n Enter any Number:”);
scanf(“%d”, &num);
printf(“Multiplication table of %d: \n”, num); while (i <= 10) { printf(“\n %d x %d = %d”, num, i, num * i); i++; }
return 0;

}

Output:

Enter any Number:5
5 x 1 = 5
5 x 2 = 10 5 x 3 = 15 5 x 4 = 20 5 x 5 = 25 5 x 6 = 30 5 x 7 = 35 5 x 8 = 40 5 x 9 = 45 5 x 10 = 50

Explanation:
We need to multiply the given number (i.e. the number for which we want the multiplication table) with value of ‘i’ which increments from 1 to 10.