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C PROGRAMMING NOTES

September 1 2015

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INTRODUCTION OF C

C is a general-purpose high level language that was originally developed by

Dennis Ritchie for the UNIX operating system. It was first implemented on

the Digital Equipment Corporation PDP-11 computer in 1972.

The UNIX operating system and virtually all UNIX applications are written in the C language. C has now become a widely used professional language for

various reasons.

Easy to learn

Structured language It produces efficient programs.

It can handle low-level activities. It can be compiled on a variety of computers.

WHY TO USE C

C was initially used for system development work, in particular the programs

that make-up the operating system. C was adopted as a system development language because it produces code that runs nearly as fast as

code written in assembly language. Some examples of the use of C might be:

Operating Systems Language Compilers

Assemblers Text Editors

Print Spoolers Network Drivers

Modern Programs Data Bases

Language Interpreters Utilities

FEATURES OF C

1. Low Level Features:

1. C Programming provides low level features that are generally provided by the

Lower level languages. C is Closely Related to Lower level Language such as

“Assembly Language“.

2. It is easier to write assembly language codes in C programming.

2. Portability:

1. C Programs are portable i.e. they can be run on any Compiler with Little or no

Modification

2. Compiler and Preprocessor make it Possible for C Program to run it on Different PC

3 . Powerful

1. Provides Wide verity of ‘Data Types‘

2. Provides Wide verity of ‘Functions’

3. Provides useful Control & Loop Control Statements

4 . Bit Manipulation

1. C Programs can be manipulated using bits. We can perform different operations at

bit level. We can manage memory representation at bit level. [E.g. We can use

Structure to manage Memory at Bit Level]

2. It provides wide verity of bit manipulation Operators. We have bitwise operators to

manage Data at bit level.

5 . High Level Features :

1. It is more User friendly as compare to previous languages. Previous languages such

as BCPL Pascal and other programming languages never provide such great

features to manage data.

2. Previous languages have their pros and cons but C Programming collected all

useful features of previous languages thus C become more effective language.

6 . Modular Programming

1. Modular programming is a software design technique that increases the extent

to which software is composed of separate parts, called modules

2. C Program Consist of Different Modules that are integrated together to form

complete program

7 . Efficient Use of Pointers

1. Pointers have direct access to memory.

2. C Supports efficient use of pointer.

ADVANTAGES OF C LANGUAGE

1. C language is a building block for many other currently known languages.

C language has variety of data types and powerful operators. Due to this, programs

written in C language are efficient, fast and easy to understand.

2. C is highly portable language. This means that written for one computer can easily

run on another computer without any change or by doing a little change.

3. There are only 32 keywords in ANSI C and its strength lies in its built-in functions.

Several standard functions are available which can be used for developing programs.

4. Another important advantage of C is its ability to extend itself. A C program is

basically a collection of functions that are supported by the C library this makes us

easier to add our own functions to C library. Due to the availability of large number

of functions, the programming task becomes simple.

5. C language is a structured programming language. This makes user to think of a

problem in terms of function modules or blocks. Collection of these modules makes a

complete program. This modular structure makes program debugging, testing and

maintenance easier.

Disadvantages of C Language

1. C does not have concept of OOPs, that’s why C++ is developed.

2. There is no runtime checking in C language.

3. There is no strict type checking. For example, we can pass an integer value.

for the floating data type.

4. C doesn’t have the concept of namespace.

5. C doesn’t have the concept of constructor or destructor.

Basic structure of C programming: To write a C program, we first create functions and then put them together. A C program

may contain one or more sections. They are illustrated below.

1. Documentation section : The documentation section consists of a set

of comment lines giving the name of the program, the author and other

details, which the programmer would like to use later.

2. Link section : The link section provides instructions to the compiler to link

functions from the system library.

3. Definition section : The definition section defines all symbolic constants.

4. Global declaration section : There are some variables that are used in

more than one function. Such variables are called global variables and are

declared in the global declaration section that is outside of all the functions.

This section also declares all the user-defined functions.

5. main () function section : Every C program must have one main function

section. This section contains two parts; declaration part and executable part

6. Declaration part : The declaration part declares all the variables used

in the executable part.

7. Executable part : There is at least one statement in the executable

part. These two parts must appear between the opening and closing

braces. The program execution begins at the opening brace and ends

at the closing brace. The closing brace of the main function is the

logical end of the program. All statements in the declaration and

executable part end with a semicolon.

8. Subprogram section : The subprogram section contains all the user-

defined functions that are called in the main () function. User-defined

functions are generally placed immediately after the main () function,

although they may appear in any order.

Steps to write C programs and get the output:

Below are the steps to be followed for any C program to create and get the output. This is common to all C program and there is no exception whether its a very small C program or very large C program.

Basic commands in C programming to write basic C Program:

Below are few commands and syntax used in C programming to write a simple C

program. Let’s see all the sections of a simple C program line by line.

S.no Command Explanation

1 #include <stdio.h> This is a preprocessor command that includes standard

input output header file(stdio.h) from the C library before

compiling a C program

2 int main() This is the main function from where execution of any C

program begins.

3 { This indicates the beginning of the main function.

4 /*_some_comments_*/ whatever is given inside the command “/* */” in any C

program, won’t be considered for compilation and

execution.

5 printf(“Hello_World! “); printf command prints the output onto the screen.

6 getch(); This command waits for any character input from

keyboard.

7 return 0; This command terminates C program (main function) and

returns 0.

8 } This indicates the end of the main function.

Output:

Hello

World!

.

1. Keywords are those words whose meaning is already defined by Compiler

2. Cannot be used as Variable Name

3. There are 32 Keywords in C

4. C Keywords are also called as Reserved words .

32 Keywords in C Programming Language

Auto double int struct

Break else long switch

Case enum register typedef

Char extern return union

Const float short unsigned

continue for signed void

default goto sizeof volatile

Do if static while

C Tokens Chart

In C Programming punctuation, individual words, characters etc are called

tokens.

Tokens are basic building blocks of C Programming

Token Example :

No Token Type Example 1 Example 2

1 Keyword do while

2 Constants number sum

3 Identifier -76 89

4 String “HTF” “PRIT”

5 Special Symbol * @

6 Operators ++ /

Basic Building Blocks and Definition :

Token Meaning

Keyword A variable is a meaningful name of data storage location in computer memory. When

using a variable you refer to memory address of computer

Constant Constants are expressions with a fixed value

Identifier The term identifier is usually used for variable names

String Sequence of characters

Special Symbols other than the Alphabets and Digits and white-spaces

Operators A symbol that represent a specific mathematical or non mathematical action

C Constants are also like normal variables. But, only difference is, their values can not be modified by the program once they are defined.

Constants refer to fixed values. They are also called as literals Constants may be belonging to any of the data type.

Syntax:

const data_type variable_name; (or) const data_type *variable_name;

Types of C constant:

1. Integer constants 2. Real or Floating point constants 3. Octal & Hexadecimal constants 4. Character constants 5. String constants 6. Backslash character constants

S.no Constant type data type Example

1 Integer constants int

unsigned int

long int

long long int

53, 762, -478 etc

5000u, 1000U etc

483,647

2,147,483,680

2 Real or Floating point constants float

doule

10.456789

600.123456789

3 Octal constant int 013 /* starts with 0 */

4 Hexadecimal constant int 0×90 /* starts with 0x */

5 character constants char ‘A’ , ‘B’, ‘C’

6 string constants char “ABCD” , “Hai”

Rules for constructing C constant:

1. Integer Constants in C:

An integer constant must have at least one digit. It must not have a decimal point. It can either be positive or negative. No commas or blanks are allowed within an integer constant. If no sign precedes an integer constant, it is assumed to be positive. The allowable range for integer constants is -32768 to 32767.

2. Real constants in C:

A real constant must have at least one digit It must have a decimal point It could be either positive or negative If no sign precedes an integer constant, it is assumed to be positive. No commas or blanks are allowed within a real constant.

3. Character and string constants in C:

A character constant is a single alphabet, a single digit or a single special symbol enclosed within single quotes.

The maximum length of a character constant is 1 character. String constants are enclosed within double quotes.

4. Backslash Character Constants in C:

There are some characters which have special meaning in C language. They should be preceded by backslash symbol to make use of special function of

them. Given below is the list of special characters and their purpose.

Backslash_character Meaning

\b Backspace

\f Form feed

\n New line

\r Carriage return

\t Horizontal tab

\” Double quote

\’ Single quote

\\ Backslash

\v Vertical tab

\a Alert or bell

\? Question mark

\N Octal constant (N is an octal constant)

\XN Hexadecimal constant (N – hex.dcml cnst)

How to use constants in a C program?

We can define constants in a C program in the following ways.

1. By “const” keyword 2. By “#define” preprocessor directive

Please note that when you try to change constant values after defining in C program, it will through error.

1. Example program using const keyword in C:

#include <stdio.h>

void main()

{

const int height = 100; /*int constant*/

const float number = 3.14; /*Real constant*/

const char letter = ‘A’; /*char constant*/

const char letter_sequence[10] = “ABC”; /*string

constant*/

const char backslash_char =

‘\?’; /*special char cnst*/

printf(“value of height :%d \n”, height );

printf(“value of number : %f \n”, number );

printf(“value of letter : %c \n”, letter );

printf(“value of letter_sequence : %s \n”, letter_sequence);

printf(“value of backslash_char : %c \n”, backslash_char);

}

Output:

value of height : 100

value of number : 3.140000

value of letter : A

value of letter_sequence : ABC

value of backslash_char : ?

C data types are defined as the data storage format that a variable can store a data to perform a specific operation.

Data types are used to define a variable before to use in a program. Size of variable, constant and array are determined by data types.

Data types:

There are four data types in C language. They are,

S.no Types Data Types

1 Basic data types int, char, float, double

2 Enumeration data type enum

3 Derived data type pointer, array, structure, union

4 Void data type void

1. Basic data types in C:

1.1. Integer data type:

Integer data type allows a variable to store numeric values. “int” keyword is used to refer integer data type. The storage size of int data type is 2 or 4 or 8 byte. It varies depend upon the processor in the CPU that we use. If we are using 16

bit processor, 2 byte (16 bit) of memory will be allocated for int data type. Like wise, 4 byte (32 bit) of memory for 32 bit processor and 8 byte (64 bit) of

memory for 64 bit processor is allocated for int datatype. int (2 byte) can store values from -32,768 to +32,767 int (4 byte) can store values from -2,147,483,648 to +2,147,483,647. If you want to use the integer value that crosses the above limit, you can go for

“long int” and “long long int” for which the limits are very high.

Note:

We can’t store decimal values using int data type. If we use int data type to store decimal values, decimal values will be truncated

and we will get only whole number. In this case, float data type can be used to store decimal values in a variable.

1.2. Character data type:

Character data type allows a variable to store only one character. Storage size of character data type is 1. We can store only one character using

character data type. “char” keyword is used to refer character data type. For example, ‘A’ can be stored using char datatype. You can’t store more than

one character using char data type. Please refer C – Strings topic to know how to store more than one characters in

a variable.

1.3. Floating point data type:

Floating point data type consists of 2 types. They are,

1. float 2. double

1. float:

Float data type allows a variable to store decimal values. Storage size of float data type is 4. This also varies depend upon the processor

in the CPU as “int” data type. We can use up-to 6 digits after decimal using float data type. For example, 10.456789 can be stored in a variable using float data type.

2. double:

Double data type is also same as float data type which allows up-to 10 digits after decimal.

The range for double datatype is from 1E–37 to 1E+37.

1.3.1. sizeof() function in C:

sizeof() function is used to find the memory space allocated for each C data types.

#include <stdio.h>

#include <limits.h>

int main()

{

int a;

char b;

float c;

double d;

printf(“Storage size for int data type:%d \n”,sizeof(a));

printf(“Storage size for char data type:%d \n”,sizeof(b));

printf(“Storage size for float data type:%d \n”,sizeof(c));

printf(“Storage size for double data type:%d\n”,sizeof(d));

return 0;

} .

Output:

Storage size for int data type:4

Storage size for char data type:1

Storage size for float data type:4

Storage size for double data

type:8 .

The symbols which are used to perform logical and mathematical operations in a C program are called C operators.

These C operators join individual constants and variables to form expressions. Operators, functions, constants and variables are combined together to form

expressions. Consider the expression A + B * 5. Where, +, * are operators, A, B are variables,

5 is constant and A + B * 5 is an expression.

Types of C operators:

C language offers many types of operators. They are,

1. Arithmetic operators 2. Assignment operators 3. Relational operators 4. Logical operators 5. Bit wise operators 6. Conditional operators (ternary operators) 7. Increment/decrement operators 8. Special operators

Continue on types of C operators:

Click on each operators name below for detail description and example programs.

S.no Types of Operators Description

1 Arithmetic_operators These are used to perform mathematical

calculations like addition, subtraction,

multiplication, division and modulus

2 Assignment_operators These are used to assign the values for the

variables in C programs.

3 Relational operators These operators are used to compare the

value of two variables.

4 Logical operators These operators are used to perform logical

operations on the given two variables.

5 Bit wise operators These operators are used to perform bit

operations on given two variables.

6 Conditional (ternary)

operators

Conditional operators return one value if

condition is true and returns another value

is condition is false.

7 Increment/decrement

operators

These operators are used to either increase

or decrease the value of the variable by

one.

8 Special operators &, *, sizeof( ) and ternary operators.

Decision control statements

Whenever we build an application in any programming language, there is a need of

including decision control statements in code. We can include various conditions in

our program using these statements; we can perform different- different tasks based

on the conditions. Following are the decision control statements available in C.

a) if statement

b) if-else & else-if statement

c) switch-case statements

Below are the tutorials links –

1. If statement: The code inside if body executes only when the condition defined

by if statement is true. If the condition is false then compiler skips the statement

enclosed in if’s body. We can have any number of if statements in a C program.

2. If-else statement: Here, we have two block of statements. If condition results

true then if block gets execution otherwise statements in elseblock executes. else

cannot exist without if statement. In this tutorial, I have covered else-if

statements too.

3. Switch-case statement: This is very useful when we have several block of

statements, which requires execution based on the output of an expression or

condition. switch defines an expression (or condition) and case has a block of

statements, based on the result of expression, corresponding case gets execution.

A switch can have any number of cases, however there should be only default

handler.

Decision

control

statements

Syntax Description

if if (condition)

{ Statements; }

In these type of statements, if condition is

true, then respective block of code is

executed.

if…else if (condition)

{ Statement1; Statement2;

}

else

{ Statement3; Statement4;

}

In these type of statements, group of

statements are executed when condition is

true. If condition is false, then else part

statements are executed.

nested if if

(condition1){ Statement1; }

else_if(condition2)

{ Statement2; }

else Statement 3;

If condition 1 is false, then condition 2 is

checked and statements are executed if it is

true. If condition 2 also gets failure, then else

part is executed.

Example program for if statement in C:

In “if” control statement, respective block of code is executed when condition is true.

int main()

{

int m=40,n=40;

if (m == n)

{

printf("m and n are equal");

}

}

Output:

m and n are equal

Example program for if else statement in C:

In C if else control statement, group of statements are executed when condition is

true. If condition is false, then else part statements are executed.

#include <stdio.h>

int main()

{

int m=40,n=20;

if (m == n)

{

printf("m and n are equal");

}

else

{

printf("m and n are not equal");

}

}

Output:

m and n are not equal

Example program for nested if statement in C:

In “nested if” control statement, if condition 1 is false, then condition 2 is

checked and statements are executed if it is true. If condition 2 also gets failure, then else part is executed.

#include <stdio.h>

int main()

{

int m=40,n=20;

if (m>n) {

printf("m is greater than n");

}

else if(m<n) {

printf("m is less than n");

}

else {

printf("m is equal to n");

}

}

Output:

m is greater than n

#include <stdio.h>

main()

{

int Grade = 'A';

switch( Grade )

{

case 'A' : printf( "Excellent\n" );

case 'B' : printf( "Good\n" );

case 'C' : printf( "OK\n" );

case 'D' : printf( "Mmmmm....\n" );

case 'F' : printf( "You must do better than

this\n" );

default : printf( "What is your grade

anyway?\n" );

}

}

This will produce following result:

Excellent

Good

OK

Mmmmm....

You must do better than this

What is your grade anyway?

Using break statement:

You can come out of the switch block if your condition is met. This can be

achieved using break statement. Try out following example:

#include <stdio.h>

main()

{

int Grade = 'B';

switch( Grade )

{

case 'A' : printf( "Excellent\n" );

break;

case 'B' : printf( "Good\n" );

break;

case 'C' : printf( "OK\n" );

break;

case 'D' : printf( "Mmmmm....\n" );

break;

case 'F' : printf( "You must do better than

this\n" );

break;

default : printf( "What is your grade

anyway?\n" );

break;

}

}

Loops

for loop”

“while loop” “do while loop”

The for loop

The “for loop” loops from one number to another number and increases

by a specified value each time. The “for loop” uses the following structure:

for (Start value; continue or end condition; increase

value)

statement;

Look at the example below:

#include<stdio.h>

int main()

{

int i;

for (i = 0; i < 10; i++)

{

printf ("Hello\n");

printf ("World\n");

}

return 0;

}

The while loop

The while loop can be used if you don’t know how many times a loop must run. Here is an example:

#include<stdio.h>

int main()

{

int counter, howmuch;

scanf("%d", &howmuch);

counter = 0;

while ( counter < howmuch)

{

counter++;

printf("%d\n", counter);

}

return 0;

}

The do while loop

The “do while loop” is almost the same as the while loop. The “do while

loop” has the following form:

do

{

do something;

}

while (expression);

Do something first and then test if we have to continue. The result is that the

loop always runs once. (Because the expression test comes afterward). Take a

look at an example:

#include<stdio.h>

int main()

{

int counter, howmuch;

scanf("%d", &howmuch);

counter = 0;

do

{

counter++;

printf("%d\n", counter);

}

while ( counter < howmuch);

return 0;

}

Array

In C programming, one of the frequently arising problem is to handle similar

types of data. For example: If the user want to store marks of 100 students. This

can be done by creating 100 variable individually but, this process is rather

tedious and impracticable. These type of problem can be handled in C

programming using arrays.

An array is a sequence of data item of homogeneous value(same type).

Arrays are of two types:

1. One-dimensional arrays

2. Multidimensional arrays

Declaration of one-dimensional array

data_type array_name[array_size];

For example: int age[5];

Here, the name of array is age. The size of array is 5,i.e., there are 5

items(elements) of array age. All element in an array are of the same type (int, in

this case).

Array elements

Size of array defines the number of elements in an array. Each element of array

can be accessed and used by user according to the need of program. For

example:

int age[5];

Note that, the first element is numbered 0 and so on.

Here, the size of array age is 5 times the size of int because there are 5

elements.

Suppose, the starting address of age[0] is 2120d and the size of int be 4 bytes.

Then, the next address (address of a[1]) will be 2124d, address of a[2] will be

2128d and so on.

Initialization of one-dimensional array:

Arrays can be initialized at declaration time in this source code as:

int age[5]={2,4,34,3,4};

It is not necessary to define the size of arrays during initialization.

int age[]={2,4,34,3,4};

In this case, the compiler determines the size of array by calculating the number

of elements of an array.

Accessing array elements

In C programming, arrays can be accessed and treated like variables in C.

For example:

scanf("%d",&age[2]);

/* statement to insert value in the third element of array age[]. */

scanf("%d",&age[i]);

/* Statement to insert value in (i+1)th element of array age[]. */

/* Because, the first element of array is age[0], second is age[1], ith is age[i-1] and (i+1)th is age[i]. */

printf("%d",age[0]);

/* statement to print first element of an array. */

printf("%d",age[i]);

/* statement to print (i+1)th element of an array. */

Example of array in C programming

/* C program to find the sum marks of n students using arrays */

#include <stdio.h>

int main(){

int marks[10],i,n,sum=0;

printf("Enter number of students: ");

scanf("%d",&n);

for(i=0;i<n;++i){

printf("Enter marks of student%d: ",i+1);

scanf("%d",&marks[i]);

sum+=marks[i];

}

printf("Sum= %d",sum);

return 0;

}

Output

Enter number of students: 3

Enter marks of student1: 12

Enter marks of student2: 31

Enter marks of student3: 2

sum=45

C programming language allows programmer to create arrays of arrays known as

multidimensional arrays. For example:

float a[2][6];

Here, a is an array of two dimension, which is an example of multidimensional array.

For better understanding of multidimensional arrays, array elements of above example can be

thinked of as below:

Initialization of Multidimensional Arrays

In C, multidimensional arrays can be initialized in different number of ways.

int c[2][3]={{1,3,0}, {-1,5,9}};

OR

int c[][3]={{1,3,0}, {-1,5,9}};

OR

int c[2][3]={1,3,0,-1,5,9};

Initialization Of three-dimensional Array

double cprogram[3][2][4]={

{{-0.1, 0.22, 0.3, 4.3}, {2.3, 4.7, -0.9, 2}},

{{0.9, 3.6, 4.5, 4}, {1.2, 2.4, 0.22, -1}},

{{8.2, 3.12, 34.2, 0.1}, {2.1, 3.2, 4.3, -2.0}}

};

Suppose there is a multidimensional array arr[i][j][k][m]. Then this array can hold

i*j*k*m numbers of data.

Similarly, the array of any dimension can be initialized in C programming.

Example of Multidimensional Array In C

Write a C program to find sum of two matrix of order 2*2 using multidimensional arrays

where, elements of matrix are entered by user.

#include <stdio.h>

int main(){

float a[2][2], b[2][2], c[2][2];

int i,j;

printf("Enter the elements of 1st matrix\n");

/* Reading two dimensional Array with the help of two for loop. If there was an array of 'n'

dimension, 'n' numbers of loops are needed for inserting data to array.*/

for(i=0;i<2;++i)

for(j=0;j<2;++j){

printf("Enter a%d%d: ",i+1,j+1);

scanf("%f",&a[i][j]);

}

printf("Enter the elements of 2nd matrix\n");

for(i=0;i<2;++i)

for(j=0;j<2;++j){

printf("Enter b%d%d: ",i+1,j+1);

scanf("%f",&b[i][j]);

}

for(i=0;i<2;++i)

for(j=0;j<2;++j){

/* Writing the elements of multidimensional array using loop. */

c[i][j]=a[i][j]+b[i][j]; /* Sum of corresponding elements of two arrays. */

}

printf("\nSum Of Matrix:");

for(i=0;i<2;++i)

for(j=0;j<2;++j){

printf("%.1f\t",c[i][j]);

if(j==1) /* To display matrix sum in order. */

printf("\n");

}

return 0;

}

Ouput

Enter the elements of 1st matrix

Enter a11: 2;

Enter a12: 0.5;

Enter a21: -1.1;

Enter a22: 2;

Enter the elements of 2nd matrix

Enter b11: 0.2;

Enter b12: 0;

Enter b21: 0.23;

Enter b22: 23;

Sum Of Matrix:

2.2 0.5

-0.9 25.0

Strings

C Strings are nothing but array of characters ended with null character (‘\0’). This null character indicates the end of the string. Strings are always enclosed by double quotes. Whereas, character is enclosed

by single quotes in C.

Example for C string:

char string[20] = { ‘f’ , ’r’ , ‘e’ , ‘s’ , ‘h’ , ‘2’ , ‘r’ , ‘e’ , ‘f’ , ’r’ , ‘e’ , ‘s’ , ‘h’ , ‘\0’}; (or) char string[20] = “fresh2refresh”; (or) char string [] = “fresh2refresh”;

Difference between above declarations are, when we declare char as “string[20]“, 20 bytes of memory space is allocated for holding the string value.

When we declare char as “string[]”, memory space will be allocated as per the requirement during execution of the program.

Example program for C string:

#include <stdio.h>

int main ()

{

char string[20] = "fresh2refresh.com";

printf("The string is : %s \n", string );

return 0;

}

Output:

The string is : fresh2refresh.com

C String functions:

String.h header file supports all the string functions in C language. All the string functions are given below.

Click on each string function name below for detail description and example programs.

S.no String

functions

Description

1 strcat ( ) Concatenates str2 at the end of str1.

2 strncat ( ) appends a portion of string to another

3 strcpy ( ) Copies str2 into str1

4 strncpy ( ) copies given number of characters of one string to another

5 strlen ( ) gives the length of str1.

6 strcmp ( ) Returns 0 if str1 is same as str2. Returns <0 if strl < str2. Returns

>0 if str1 > str2.

7 strcmpi_(.) Same as strcmp() function. But, this function negotiates

case. “A” and “a” are treated as same.

8 strchr ( ) Returns pointer to first occurrence of char in str1.

9 strrchr ( ) last occurrence of given character in a string is found

10 strstr ( ) Returns pointer to first occurrence of str2 in str1.

11 strrstr ( ) Returns pointer to last occurrence of str2 in str1.

12 strdup ( ) duplicates the string

13 strlwr ( ) converts string to lowercase

14 strupr ( ) converts string to uppercase

15 strrev ( ) reverses the given string

16 strset ( ) sets all character in a string to given character

17 strnset ( ) It sets the portion of characters in a string to given character

18 strtok ( ) tokenizing given string using delimiter

Function

A function is a block of statements, which is used to perform a specific task. Suppose

you are building an application in C language and in one of your program, you need to

perform a same task more than once. So in such scenario you have two options –

a) Use the same set of statements every time you want to perform the task

b) Create a function, which would do the task, and just call it every time you need to

perform the same task.

Using option (b) is a good practice and a good programmer always uses functions

while writing codes.

Types of functions

1) Predefined standard library functions – such

as puts(), gets(),printf(), scanf() etc – These are the functions which already

have a definition in header files (.h files like stdio.h), so we just call them whenever

there is a need to use them.

2) User Defined functions – The functions which we can create by ourselves, for

example in the above code I have created a function abc and I called it int main() in

order to use it.

Why we need functions

Functions are used because of following reasons –

a) To improve the readability of code.

b) Improves the reusability of the code, same function can be used in any program

rather than writing the same code from scratch.

c) Debugging of the code would be easier if you use functions as errors are easy to be

traced.

d) Reduces the size of the code, duplicate set of statements are replaced by function

calls.

Syntax of Defining a function

return_type function_name (argument list)

{

Set of statements – Block of code

}

return_type: Return type can be of any data type such as int, double, char, void,

short etc. Don’t worry you will understand these terms better once you go through

the below examples.

function_name: It can be anything, however it is advised to have a meaningful name

for the functions so that it would be easy to understand the purpose of function just

by seeing it’s name.

argument list: Argument list contains variables names along with their data types.

These arguments are kind of inputs for the function. For example – A function which is

used to add two integer variables, will be having two integer argument.

Block of code: Set of C statements, which will be executed whenever a call will be

made to the function.

How to call a function?

Consider the below program –

Example1:

int addition(int num1, int num2)

{

int sum

/* Arguments are used here*/

sum = num1+num2;

/* function return type is integer so I should return some

integer value */

return sum

}

int main()

{

int var1, var2;

printf("enter number 1: ");

scanf("%d",&var1);

printf("enter number 2: ");

scanf("%d",&var2);

/* calling function – function return type is integer so I would

be

* needing to store the returned value in some integer variable

*/

int res = addition(var1, var2);

printf ("Output: %d", res);

return 0;

}

Pointers

Pointers in C are easy and fun to learn. Some C programming tasks are performed

more easily with pointers, and other tasks, such as dynamic memory allocation, cannot

be performed without using pointers. So it becomes necessary to learn pointers to

become a perfect C programmer. Let's start learning them in simple and easy steps.

As you know, every variable is a memory location and every memory location has its

address defined which can be accessed using ampersand (&) operator, which denotes

an address in memory. Consider the following example, which will print the address of

the variables defined:

#include <stdio.h>

int main ()

{

int var1;

char var2[10];

printf("Address of var1 variable: %x\n", &var1 );

printf("Address of var2 variable: %x\n", &var2 );

return 0;

}

When the above code is compiled and executed, it produces result something as

follows:

Address of var1 variable: bff5a400

Address of var2 variable: bff5a3f6

So you understood what is memory address and how to access it, so base of the

concept is over. Now let us see what is a pointer.

What Are Pointers?

A pointer is a variable whose value is the address of another variable, i.e., direct

address of the memory location. Like any variable or constant, you must declare a

pointer before you can use it to store any variable address. The general form of a

pointer variable declaration is:

type *var-name;

Here, type is the pointer's base type; it must be a valid C data type and var-name is

the name of the pointer variable. The asterisk * you used to declare a pointer is the

same asterisk that you use for multiplication. However, in this statement the asterisk is

being used to designate a variable as a pointer. Following are the valid pointer

declaration:

int *ip; /* pointer to an integer */

double *dp; /* pointer to a double */

float *fp; /* pointer to a float */

char *ch /* pointer to a character */

The actual data type of the value of all pointers, whether integer, float, character, or

otherwise, is the same, a long hexadecimal number that represents a memory address.

The only difference between pointers of different data types is the data type of the

variable or constant that the pointer points to.

How to use Pointers?

There are few important operations, which we will do with the help of pointers very

frequently.(a) we define a pointer variable (b) assign the address of a variable to a

pointer and (c) finally access the value at the address available in the pointer variable.

This is done by using unary operator * that returns the value of the variable located at

the address specified by its operand. Following example makes use of these

operations:

#include <stdio.h>

int main ()

{

int var = 20; /* actual variable declaration */

int *ip; /* pointer variable declaration */

ip = &var; /* store address of var in pointer variable*/

printf("Address of var variable: %x\n", &var );

/* address stored in pointer variable */

printf("Address stored in ip variable: %x\n", ip );

/* access the value using the pointer */

printf("Value of *ip variable: %d\n", *ip );

return 0;

}

When the above code is compiled and executed, it produces result something as

follows:

Address of var variable: bffd8b3c

Address stored in ip variable: bffd8b3c

Value of *ip variable: 20

NULL Pointers in C

It is always a good practice to assign a NULL value to a pointer variable in case you do

not have exact address to be assigned. This is done at the time of variable declaration.

A pointer that is assigned NULL is called a null pointer.

The NULL pointer is a constant with a value of zero defined in several standard

libraries. Consider the following program:

#include <stdio.h>

int main ()

{

int *ptr = NULL;

printf("The value of ptr is : %x\n", ptr );

return 0;

}

When the above code is compiled and executed, it produces the following result:

The value of ptr is 0

On most of the operating systems, programs are not permitted to access memory at

address 0 because that memory is reserved by the operating system. However, the

memory address 0 has special significance; it signals that the pointer is not intended to

point to an accessible memory location. But by convention, if a pointer contains the null

(zero) value, it is assumed to point to nothing.

To check for a null pointer you can use an if statement as follows:

if(ptr) /* succeeds if p is not null */

if(!ptr) /* succeeds if p is null */

C Pointers in Detail:

Pointers have many but easy concepts and they are very important to C programming.

There are following few important pointer concepts which should be clear to a C

programmer:

Concept Description

C - Pointer arithmetic

There are four arithmetic operators that

can be used on pointers: ++, --, +, -

C - Array of pointers

You can define arrays to hold a number of

pointers.

C - Pointer to pointer

C allows you to have pointer on a pointer

and so on.

Passing pointers to functions in C

Passing an argument by reference or by

address both enable the passed argument

to be changed in the calling function by the

called function.

Return pointer from functions in C

C allows a function to return a pointer to

local variable, static variable and

dynamically allocated memory as well.

Structures

C arrays allow you to define type of variables that can hold several data items of the

same kind but structure is another user defined data type available in C programming,

which allows you to combine data items of different kinds.

Structures are used to represent a record, suppose you want to keep track of your

books in a library. You might want to track the following attributes about each book:

Title

Author

Subject

Book ID

Defining a Structure

To define a structure, you must use the struct statement. The struct statement defines

a new data type, with more than one member for your program. The format of the

struct statement is this:

struct [structure tag]

{

member definition;

member definition;

...

member definition;

} [one or more structure variables];

The structure tag is optional and each member definition is a normal variable

definition, such as int i; or float f; or any other valid variable definition. At the end of the

structure's definition, before the final semicolon, you can specify one or more structure

variables but it is optional. Here is the way you would declare the Book structure:

struct Books

{

char title[50];

char author[50];

char subject[100];

int book_id;

} book;

Accessing Structure Members

To access any member of a structure, we use the member access operator (.). The

member access operator is coded as a period between the structure variable name

and the structure member that we wish to access. You would use struct keyword to

define variables of structure type. Following is the example to explain usage of

structure:

#include <stdio.h>

#include <string.h>

struct Books

{

char title[50];

char author[50];

char subject[100];

int book_id;

};

int main( )

{

struct Books Book1; /* Declare Book1 of type Book */

struct Books Book2; /* Declare Book2 of type Book */

/* book 1 specification */

strcpy( Book1.title, "C Programming");

strcpy( Book1.author, "Nuha Ali");

strcpy( Book1.subject, "C Programming Tutorial");

Book1.book_id = 6495407;

/* book 2 specification */

strcpy( Book2.title, "Telecom Billing");

strcpy( Book2.author, "Zara Ali");

strcpy( Book2.subject, "Telecom Billing Tutorial");

Book2.book_id = 6495700;

/* print Book1 info */

printf( "Book 1 title : %s\n", Book1.title);

printf( "Book 1 author : %s\n", Book1.author);

printf( "Book 1 subject : %s\n", Book1.subject);

printf( "Book 1 book_id : %d\n", Book1.book_id);

/* print Book2 info */

printf( "Book 2 title : %s\n", Book2.title);

printf( "Book 2 author : %s\n", Book2.author);

printf( "Book 2 subject : %s\n", Book2.subject);

printf( "Book 2 book_id : %d\n", Book2.book_id);

return 0;

}

Union

A union is a special data type available in C that enables you to store different data

types in the same memory location. You can define a union with many members, but

only one member can contain a value at any given time. Unions provide an efficient

way of using the same memory location for multi-purpose.

Defining a Union

To define a union, you must use the union statement in very similar was as you did

while defining structure. The union statement defines a new data type, with more than

one member for your program. The format of the union statement is as follows:

union [union tag]

{

member definition;

member definition;

...

member definition;

} [one or more union variables];

The union tag is optional and each member definition is a normal variable definition,

such as int i; or float f; or any other valid variable definition. At the end of the union's

definition, before the final semicolon, you can specify one or more union variables but it

is optional. Here is the way you would define a union type named Data which has the

three members i, f, and str:

union Data

{

int i;

float f;

char str[20];

} data;

Now, a variable of Data type can store an integer, a floating-point number, or a string

of characters. This means that a single variable ie. same memory location can be used

to store multiple types of data. You can use any built-in or user defined data types

inside a union based on your requirement.

File Handling in C Language

A file represents a sequence of bytes on the disk where a group of related data is

stored. File is created for permanent storage of data. It is a ready made structure.

In C language, we use a structure pointer of file type to declare a file.

FILE *fp;

C provides a number of functions that helps to perform basic file operations. Following

are the functions,

Function Description

fopen() create a new file or open a existing file

fclose() closes a file

getc() reads a character from a file

putc() writes a character to a file

fscanf() reads a set of data from a file

fprintf() writes a set of data to a file

getw() reads a integer from a file

putw() writes a integer to a file

fseek() set the position to desire point

ftell() gives current position in the file

rewind() set the position to the begining point

Opening a File or Creating a File

The fopen() function is used to create a new file or to open an existing file.

General Syntax :

*fp = FILE *fopen(const char *filename, const char *mode);

Here filename is the name of the file to be opened and mode specifies the purpose of

opening the file. Mode can be of following types,

*fp is the FILE pointer ( FILE *fp ), which will hold the reference to the opened(or

created) file.

mode description

r opens a text file in reading mode

w opens or create a text file in writing mode.

a opens a text file in append mode

r+ opens a text file in both reading and writing mode

w+ opens a text file in both reading and writing mode

a+ opens a text file in both reading and writing mode

rb opens a binary file in reading mode

wb opens or create a binary file in writing mode

ab opens a binary file in append mode

rb+ opens a binary file in both reading and writing mode

wb+ opens a binary file in both reading and writing mode

ab+ opens a binary file in both reading and writing mode

Closing a File

The fclose() function is used to close an already opened file.

General Syntax :

int fclose( FILE *fp );

Here fclose() function closes the file and returns zero on success, or EOF if there is an

error in closing the file. This EOF is a constant defined in the header file stdio.h.

Input/Output operation on File

In the above table we have discussed about various file I/O functions to perform reading

and writing on file. getc() and putc() are simplest functions used to read and write

individual characters to a file.

#include<stdio.h>

#include<conio.h>

main()

{

FILE *fp;

char ch;

fp = fopen("one.txt", "w");

printf("Enter data");

while( (ch = getchar()) != EOF) {

putc(ch,fp);

}

fclose(fp);

fp = fopen("one.txt", "r");

while( (ch = getc()) != EOF)

printf("%c",ch);

fclose(fp);

}

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