Learning c - An extensive guide to learn the C Language

- ABHISHEK DWIVEDI
LEARNING
5 September 2015ABHISHEK DWIVEDI

WHICH TOPIC U WANNA STUDY ???
INTRODUCTION
CONSTANTS & VARIABLES
OPERATORS & EXPRESSIONS
STRUCTURE OF A C PROGRAM
CONTROL STRUCTURES
ARRAYS AND STRINGS
FUNCTIONS
STORAGE CLASSES
STRUCTURES & UNIONS
POINTERS
DYNAMIC MEMORY ALLOCATION
FILE MANAGEMENT IN C
COMMAND LINE ARGUMENTS

C is a programming language developed at AT &T
Bell Laboratories of USA in 1972, designed and
written by Dennis Ritchie .
C is highly portable i.e., software written for one
computer can be run on another computer.
An important feature of C is its ability to extend
itself.A C program is basically a collection of
functions.
Introducing C

ALGOL Algorithmic Language
CPL Combined Programming Language
BCPL Basic Combined Programming
Language
Historical Development of C

A token is an atomic unit (smallest indivisible
units) in a program.
The most basic elements in a C program
recognized by the compiler are a single character or
a group of characters called C tokens.
The compiler cannot breakdown the token any
further. For example, the words main, { brace ,
(parenthesis) are all tokens of C program.
C Tokens

1. Keywords
Examples: float, int, double, while,
for.
2. Identifiers
Examples: main, amount
3. Constants
Examples: 12.4, 7894
4. Strings
Examples: CSM , Thursday
5. Special Symbols
Examples: [,], {, }, (, )
6. Operators
Examples: +, *, /
Types of tokens.

The C character set includes the upper case letters A to
Z, the lower case a to z, the decimal digits 0 to 9 and
certain special characters.
Letters a, b, c, ……………z
Digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Special characters ~ , . ; : ? ! [ ] { } / < > = +
- $ # @ & * % ^
The C character set

Character/
Symbol
Meaning Character/
Symbol
Meaning
~ tilde , Comma
. Period ; Semicolon
? Ques. mark : Colon
“ Double Quote ‘ Single Quote
( Left parenthesis ) Right
Parenthesis
[ Left Bracket ] Right Bracket
{ Left Brace } Right Brace
/ Slash Back Slash
< Less than > Greater than
= Equal to ! Exclamatory
Mark
- Minus + Plus
# Hash $ Dolor Sign
& Ampersand * Asterisk (or
star)
% Percent ^ Carat
_ Underscore | Vertical Bar5 September 2015ABHISHEK DWIVEDI

Identifiers are distinct names given to program
elements such as constants, variables, etc.
An Identifier is a sequence of letters, digits, and the
special character _ underscore .
1. It must start with either a letter or
underscore. _
2. No commas or blanks are allowed within a
variable name.
3.The upper case and lower case letters are
treated as distinct, i.e., identifiers are
case-sensitive.
4. An identifier can be of any length.
5. No special symbol can be used in a variable
name.
Identifiers

Keywords are predefined tokens in C.
These are also called reserved words.
Key words have special meaning to the
C compiler. These key words can be
used only for their intended action; they
cannot be used for any other purpose.
C has 32 keywords.
Keywords

auto break case char const
continue default do double else
enum extern float for goto
if int long register return
short signed sizeof static struct
switch typedef union unsigned void
volatile while
The standard keywords are

A data type defines a set of values and
the operations that can be performed on
them.
Every datatype item (constant, variable
etc.) in a C program has a datatype
associated with it.
C also has a special datatype called void,
which, indicates that any data type, i.e., no
data type, does not describe the data
items.
Data types

Data types Description
Size (No. of
Bytes)
Range
Char Single character 1 0 to 255
Int An integer 2 -32768 to +32767
Float Floating point number 4 -2,147,483,648 to
+2,147,483,647
Double Floating point number 8 Approximately 15
digits of Precision
Void No data type 0
signed char Character 1 -128 to 127
unsigned char Unsigned character 1 0 to 255
short signed int Short signed integer 2 -32768 to +32767
short unsigned int Short unsigned
integer
3 0 to 65535
Long singed int Long signed integer 4 -2,147,483,648 to
+2,147,483,647

A constant is a literal, which remain
unchanged during the execution of a
program.
A constant is a fixed value that cannot be
altered during the execution of a program.
C constants can be classified into two
categories.
Primary Constants
Secondary Constants
Constants and Variables

An integer constant must have at least one digit.
It should not contain either a decimal point or exponent.
If a constant is positive, it may or may not be preceded by a
plus sign. If it is a negative, it must be preceded by a
minus sign.
Commas, blanks and non-digit characters are not allowed in
integer constants.
The value of integer constant cannot exceed specified limits.
The valid range is
–32768 to +32767.
Rules for constructing Integer constants

Real values are often called floating-point constants. There
are two ways to represent a real constant decimal form and
exponential form.
In exponential form of representation, the real constant is
represented in two parts. The part appearing before e is
called mantissa, whereas the part following e is called
exponent.
Real constants

The mantissa part and the exponential part should be
separated by a letter e.
The mantissa part may have a positive or negative sign.
Default sign of mantissa part is positive.
The exponent must have at least one digit, which must be
a positive or negative integer. Default sign is
positive.
Range of real constants expressed in exponential form is
- 3.4e38 to 3.4e38.
Rules for constructing Real constants

A character constant is a single alphabet, a single digit or a
single special symbol enclosed within single inverted
commas. Both the inverted commas point to the left.
For example, A is valid character constant whereas A
is not.
The maximum length of a character constant can be 1
character.
Note: Every character has its ASCII (American Standard
Code for Information Interchange) value. That means every
character is interchange with integer constant. For
example, A value is 65 and a value is 97.
Rules for constructing Characters constants

A string constant is a sequence of characters enclosed in
double quotes. The characters may be letters,
numbers, blank space or special characters.
Note that is null string or empty string. And the
single string constant A is not equivalent to the
single character constant A.
Each string constant must end with a special character .
This character is called null character and used to
terminate the string.The compiler automatically
places a null character at the end of every
string constant.
String constants

Some non-printing characters and some other characters such as double
quote , single quote , question mark ? and backslash ), require an
escape sequence. A list of commonly used backslash character constants is
given below.
Escape sequence
Escape
Sequence
Meaning ASCII value
Escape
Sequence
Meaning ASCII value
a Bell 7 r Carriage
return
13
b Back Space 8 Double
Quote
34
t Tab 9 Single Quote 39
n New line 10 ? Question
Mark
63
v Vertical tab 11 Back Slash 92
f Form feed 12 0 Null 0

A variable can be considered as a name given to the location
in memory.
The term variable is used to denote any value that is referred
to a name instead of explicit value.
A variable is able to hold different values during execution of
a program, where as a constant is restricted to just one
value.
For example, in the equation 2x + 3y = 10; since x and y can
change, they are variables, whereas 2,3 and 10 cannot
change, hence they are constants. The total equation
is known as expression.
Variables

The name of a variable is composed of one to several characters,
the first of which must be a letter .
No special characters other than letters, digits, and underscore can
be used in variable name. Some compilers permit underscore as the
first character.
Commas or Blanks are not allowed with in a variable name.
Upper case and Lower case letters are significant. That is the
variable income is not same as )NCOME .
The variable name should not be a C key word. Also it should not
have the same name as a function that is written either by user or
already exist in the C library.
Rules for constructing variable names

There are basically four types of instructions in C:
Type Declaration Instruction
Input/Output Instruction
Arithmetic Instruction
Control Instruction
C Instructions

The purpose of each instructions
Type Declaration
instruction
to declare the type of
variables used in a C program
Input/Output instruction To perform the function of
supplying input data to a
program and obtaining the
output results from it.
Arithmetic instruction to perform arithmetic
operations between
constants and variables.
Control instruction to control the sequence of
execution of various
statements in a C program.

An operator is a symbol that tells the computer to
perform certain mathematical or logical
manipulations.
Operators are used in program to manipulate data
and variables.The data items that operators
act upon are called operands.
Some operators require two operands, while
others act upon only one operand.The
operators are classified into unary, binary and
ternary depending on whether they operate on
one, two or three operands respectively.
Operators & Expressions

C has four classes of operators
1. Arithmetic Operators
2. Relational Operators
3. Logical Operators
4. Bit-wise Operators
In addition, C has some special operators, which
are unique to C, they are
1. Increment & Decrement Operators
2. Conditional Operators
3. Assignment Operators, etc.
Types of operators

There are five arithmetic operators in C.
The following table lists the arithmetic operators allowed in C:
Arithmetic Operators
Operator Meaning
+ Addition
_ Subtraction; also for unary minus
* Multiplication
/ Division
% Modulo division (remainder after integer
division)

Relational Operators are symbols that are used to test the relationship
between two variables or between a variable and a constant. We often
compare two quantities, and depending on their relation takes certain
decisions. These comparisons can be done with the help of relational
operators.
C has six relational operators as shown below.
Relational Operators
Operator Meaning
> Greater than
>= Greater than or Equal to
< Less than
<= Less than or Equal to
== Equal to
!= Not equal to

Logical Operators are symbols that are used to combine or negate
expressions containing relational operators.
C has three logical operators as defined below.
Logical Operators
Operator Meaning
&& Logical AND
|| Logical OR
! Logical NOT

The lowest logical element in the memory is bit. C allows the
programmer to interact directly with the hardware of a particular
system through bitwise operators and expression.
These operators work only with int and char datatypes and cannot
be used with float and double type.
The following table shows the bitwise operators that are available in
C.
Bitwise operators
Operator Meaning
- One s Complement
| Bitwise OR
& Bitwise AND
^ Bitwise Exclusive OR (XOR)
>> Right Shift
<< Left Shift

C has two very useful operators for adding and subtracting a variable.
These are the increment and decrement operators, ++ and -- .These two
operators are unary operators.
The increment operator ++ adds 1 to its operand, and the decrement
operator -- subtracts 1 from its operand. Therefore, the following are
equivalent operations.
++i is equivalent to i = i + 1;
--i is equivalent to i = i – 1;
These operators are very useful in loops.
Increment & Decrement operators

In addition to usual assignment operator =, C has a set of shorthand operators, that
simplifies the coding of a certain type of assignment statement.
It is of the form
var op = exp
where var is a variable, op is a C binary arithmetic operator and exp is an
expression.
Assignment operators
Statement Equivalent Statement
a + = b a = a + b
a - = b a = a - b
a * =b a = a * b
a * = b + c a = a * ( b+ c)
a % = b a = a % b
a * = a a = a * a

C provides a peculiar operator ? : which is useful in reducing the code. It is
ternary operator requiring three operands.
The general format is
exp1 ? exp2 : exp3;
where exp1, exp2 and exp3 are expressions.
In the above conditional expression, exp1 is evaluated first. If the value of
exp1 is non zero (true), then the value returned will be exp2. if the value
of exp1 is zero (false), then the value returned will be exp3.
Conditional Operator

The priority or precedence in which the operations of an arithmetic
statement are performed is called the hierarchy of operators.
The operators of at the higher level of precedence are evaluated first. The
operators of the same precedence are evaluated either from left to right
or from right to left, depending on the level. This is known as the
Associativity property of an operator.
PRECEDENCEOF OPERATORS (Arithmetic operators only)
Hierarchy (precedence) of operators
Operator Description Associativity Rank
* Multiplication Left to right 3
/ Division 3
% Modulo 3
+ Addition 4
- Subtraction 4

C programs consist of one or more functions. Each function performs a
specific task. A function is a group or sequence of C statements that are
executed together.
The following is a simple C program that prints a message on the screen.
/* A simple program for printing a message */
# include <stdio.h>
# include <conio.h>
void main( )
{
clrscr( );
printf Welcome to C ;
getch( );
}
Structure of a ‘C’ program

The first line
/* A simple program for printing a message */
is a comment line. Comments in the c program are optional and may
appear anywhere in a C program. Comments are enclosed between /*
and */.
The second line
# include <stdio.h>
tells the compiler to read the file stdio.h and include its contents in this
file. stdio.h, one of header files, contain the information about input and
output functions. stdio.h means Standard Input Output Header file.This
file contains the information about printf() function.
Description

The third line
# include <conio.h>
tells the compiler to read the file conio.h and include its contents in this file.
conio.h means Consoled Input Output Header file. This file contains the
information about clrscr() and getch() functions.
The fourth line
void main( )
is the stat of the main program. The word main is followed by a pair of ordinary
parenthesis ( ), which indicates that main is also a function.
The fifth line
{
the left brace represents the beginning of the program.
The sixth line
clrscr( );
tells the compiler to clear the screen and kept the cursor at left side corner.
Description (contd…)

The seventh line
printf Welcome to C ;
this function causes its arguments to be printed on the screen on the
computer.
The eight line
getch( );
is reads the single character directly from the keyboard without printing
on the screen.
The ninth line
}
the right brace represents the ending of the program.
Description (contd…)

1. All C statements must end with semicolon.
2. C is case-sensitive.That is, upper case and lower case characters
are different. Generally the statements are typed in lower case.
3. A C statement can be written in one line or it can split into multiple
lines.
4. Braces must always match upon pairs, i.e., every opening brace {
must have a matching closing brace }.
5. Every C program starts with void main( ) function.
6. Comments cannot be nested. For example,
/*Welcome to C ,/* programming*/ */
A comment can be split into more than one line.
Rules to write a C program

Steps to be followed in writing and running a C program.
Creation of Source Program
Create a C program file in various C compilers are available under MS-DOS,
Turbo C Editor etc.
Compilation of the Program
Turbo C compiler is user friendly and provides integrated program
development environment. Thus, selecting key combination can do
compilation. That means press Alt + F9 for compilation.
Program Execution
InTurbo C environment, the RUN option will do the compilation and
execution of a program. Press Ctrl + F9 for execution the program.
Execution of C Program

The printf( ) function is used to write information to standard output
(normally monitor screen). The structure of this function is
printf(format string, list of arguments);
The format string contains the following:
1. Characters that are simply printed on the screen.
2. Specifications that begin with a % sign and define the output format
for display of each item.
3. Escape sequence characters that begin with a sign such as n, t, b
etc.
printf( ) Function: Writing Output Data
Character Argument Resulting Output
c Character A single character
d Integer Signed decimal integer
s String Prints character strings
f Floating
point
Single floating point number

The real power of a technical C program is its ability to interact with the
program user. This means that the program gets input values for variables
from users.
The scanf( ) function is a built-in C function that allows a program to get
user input from the keyboard. The structure of this function is
scanf(format string &list of arguments);
Examples
scanf %d , &a ;
scanf %d %c %f ,&a, &b, &c ;
scanf( ) Function: getting user input

The control flow statements of a language determine the order in which
the statements are executed.
We also need to be able to specify that a statement, or a group of
statements, is to be carried out conditionally, only if some condition is
true.
Also we need to be able to carry out a statement or a group of statements
repeatedly based on certain conditions.
These kinds of situations are described in C using Conditional Control and
Loop Control structures.
CONTROL STRUCTURES

A conditional structure can be implemented in C using
The if statement
The if-else statement
The nested if-else statement
The switch statement.
whereas loop control structures can be implemented in C using
while loop
do-while loop
for statement
Conditional & loop structures

The if statement is used to control the flow of execution of statements.
The general form of if statement is
if (condition)
statement;
Suppose if it is required to include more than one statement, then a
compound statement is used, in place of single statement. The form of
compound statement is
if (condition)
{
statement1;
statement2;
}
If the condition is true, then the statement/statements will be executed.
If the condition is false, then the statement/statements will not be
executed.
The if statement

Program
/* Inputting year is Leap or not */
#include<stdio.h>
#include<conio.h>
void main()
{
int year;
clrscr();
printf Enter year: ;
scanf %d ,&year);
if(year%4==0)
printf Leap year ;
if(year%4!=0)
printf Not leap year ;
getch();
}
The if statement : Program
Output 1
Enter year:1990
Not leap year
Output 2
Enter year:1996
Leap year

The general form of if-else statement is…
if (condition)
statement1;
else
statement2;
If the condition is true, then statement1 is executed. Otherwise if the condition is
false, then the statement2 is executed. Here statements statement1 and statement2
are either simple statements or compound statements.
That is…
if (condtion)
{
statements /* if block */
}
else
{
statements /* else */
}
The if-else Statement

Program
/* Single digit or not */
#include<stdio.h>
#include<conio.h>
void main()
{
int n;
clrscr();
printf Enter a number: ;
scanf %d ,&n);
if(n<=9)
printf Single digit ;
else
printf Not single digit ;
getch();
}
The if-else Statement : Program
Output 1
Enter a number:5
Single digit
Output 2
Enter a number:12
Not single digit

When a series of conditions are involved, we can use more than one if-else
statement in nested form.
This form is also known as if-else if-else statements. The general form of
if-else if-else statement is
if (condition)
statements;
else if (condition)
statements;
else
statements;
Note that a program contains number of else if statements and must be
ended with else statement.
Nested if-else Statements

Program
/*To check whether +ve, -ve or zero */
#include<stdio.h>
#include<conio.h>
void main()
{
int n;
clrscr();
printf Enter a number: ;
scanf %d ,&n);
If(n>0)
printf +ve ;
else if(n<0)
printf -ve ;
else
printf zero ;
getch();
}
Nested if-else Statements : Program
Output 1
Enter a number: -2
-ve
Output 2
Enter a number:0
zero
Output 3
Enter a number:5
+ve

The Switch statement is an extension of the if-else if-else statement. The
switch makes one selection when there are several choices to be made. The
direction of the branch taken by the switch statement is based on the value of
any int (or int compatible) variable or expression.
The general form of Switch statement is shown below.
switch (variable)
{
case constant1:statement 1;
case constant n:statement n;
default :statement;
}
The Switch Statement

Program
/* Letter -> color name */
#include<stdio.h>
#include<conio.h>
void main()
{
char x;
clrscr();
printf Enter a char: ;
scanf %c ,&x);
switch(x)
{
case w :printf w->white ;
break;
case b :printf b->black ;
break;
default:printf No color ;
}
getch();
}
The Switch Statement : Program
Output 1
Enter a char:w
w->white
Output 2
Enter a char:b
b->black
Output 3
Enter a char:c
No color

The exit( ) is a function in the standard library of C. This function causes
immediate termination of the program and execution control return to
the operating system.
In general, the termination to exit( ) function is 0 to indicate that
termination is normal. Other arguments may be used to indicate some
sort of an error.
The exit( ) Function

A portion of program that is executed repeatedly is called a loop.
The C programming language contains three different program
statements for program looping. They are
For loop
While loop
Do-While loop
LOOPS

The for loop is used to repeat the execution statement for some fixed
number of times.
The general form of for loop is
for(initialization;condition;increment/decrement)
statement;
where the statement is single or compound statement.
initialization is the initialization expression, usually an assignment to the
loop-control variable. This is performed once before the loop actually
begins execution.
condition is the test expression, which evaluated before each iteration of
the loop, which determines when the loop will exist.
increment is the modifier expression, which changes the value of loop
control variable. This expression is executed at the end of each loop.
The For Loop

Program
/* Print 1 to 10 numbers */
#include<stdio.h>
#include<conio.h>
void main()
{
int i;
clrscr();
for(i=1;i<=10;i++)
printf n%d ,i);
getch();
}
The For Loop : Program
Output
1
2
3
4
5
6
7
8
9
10

The while loop is best suited to repeat a statement or a set of statements
as long as some condition is satisfied.
The general form of while loop is
initial expression;
while(conditional-expression)
{
statement;
increment/decrement;
}
where the statement (body of the loop) may be a single statement
or a compound statements. The expression (test condition) must results
zero or non-zero.
The While Loop

Program
/* Print a message 3 times */
#include<stdio.h>
#include<conio.h>
void main()
{
int i=1;
clrscr();
while(i<=3)
{
printf nJiffy Solutions ;
i++;
}
getch();
}
The While Loop : Program
Output
Jiffy Solutions
Jiffy Solutions
Jiffy Solutions

The structure of do-while loop is similar to while loop. The difference is
that in case of do-while loop the expression is evaluated after the body of
loop is executed. In case of while loop the expression is evaluated before
executing body of loop.
The general form of do-while statement is
do
{
statement;
}while(expression);
where statement is a single statement or compound statement. In
contrast to while loop statement (body of loop), do-while loop is executed
one or more times.
The do-while loop

An Array is a collection of same data type. The elements of an array are
referred by a common name and are differentiate from one another by their
position with in an array. The elements of an array can be of any data type but
all elements in an array must be of the same type.
The general form of declaring a array is
type array_name[size];
where type is a valid datatype, array_name is the name of the array and size
is the number of elements that array_name contains.
Example:
int A[100];
int data type of elements that an array
A name of array
100 size of an array
ARRAYS

The individual elements of an array can be referenced by means of its subscript (or
index)
SupposeA is an array of 20 elements, we can reference each element as
A[0] 1st element
A[1] 2nd element
A[2] 3rd element
:
:
A[19] 20th element
Note: Subscript enclosed within parenthesis.
In C subscript starts from 0. That is, if we declare an array of size n, then we can refer the
elements from 0 to (n-1)th element.
Arrays are of 3 types. They are
Single Dimensional Array
Double Dimensional Array
Multi Dimensional Array
ARRAYS (Contd…)

The general form of Single Dimensional array is:
datatype variable[size];
Example:
int A[20];
Initialization of arrays during declaration
Similar to other datatypes, the array also can be initialized at the time of
declaration.
int num[5] ={3,2,1,5,4};
char name[ ] = { c , o , m , p , u , t , e , r , s };
float rate[] = {20.5,15.75,12.34};
Single Dimensional Array

Program illustrating Single Dimensional Array
#include<stdio.h>
#include<conio.h>
void main()
{
int a[5],i;
clrscr();
printf Enter elements into an array: ;
for(i=0;i<=4;i++)
scanf %d ,&a[i]);
printf The elements are: ;
for(i=0;i<=4;i++)
printf n%d ,a[i]);
getch();
}
Single Dimensional Array : Program

The general form ofTwo-DimensionalArrays is
type array_name[row_size][column_size];
Example:
int a[2][2];
InitializingTwo-Dimensional Arrays
Like the one-dimensional arrays, following their declaration with a list of
initial values enclosed in braces may initialize two-dimensional arrays.
For example,
int a[2][2] ={1,2,5,4};
initializes the elements of the first row to zero and the second row to one.
The initialization is done row by row. The above statement can be
equivalently written as
int a[2][2]={{1,2},{5,4}};
Two-Dimensional Array

Program IllustratingTwo Dimensional arrray
#include<stdio.h>
#include<conio.h>
void main()
{
int a[2][2],i,j;
clrscr();
printf Enter elements into array: ;
for(i=0;i<=1;i++)
{
for(j=0;j<=1;j++)
{
scanf %d ,&a[i][j]);
}
}
Two-Dimensional Array : Programs
printf The elements are:n ;
for(i=0;i<=1;i++)
{
for(j=0;j<=1;j++)
{
printf %d ,a[i][j]);
}
printf n ;
}
getch();
}

A string is an array of characters. There is no string built-in data type in
C. But we can declare string as an array of characters. To recognize a
character array, it should end with a null character .
For example, the string SCIENCE would be stored as
S C ) E N C E
The length of a string is the number of characters it contains
excluding null character. Hence, the number of locations needed to store
a string is one more than length of string.
In this example, the length of the string is 7.
Handling of Character Strings

The general form of declaration of string variable is
char string-name[size];
where, string-name is the name of a string and size is the maximum
number of characters the string-name can contain.
Example:
char name[30];
String variables can be initialized at the time of declaration.
Example:
char name[ ] = Millennium ;
A string can also be initialized at the time of declaration in the following ways.
char name[ ] = Millennium ;
or
char name[ ] ={ M , i , l , l , n , n , i , u , m , };
Declaring and initializing string variables

The scanf(), printf() function is used with %s with format specification to
read and print a string.
Example:
char str[30];
scanf %s ,str);
printf %s ,str);
In the case of reading strings, the ampersand (&) is not required before
the string variable name.As mentioned earlier, one of the limitations of
the scanf() function is that it is not capable of holding multiword strings,
even though it can read them.
Reading and writing strings

Program
#include<stdio.h>
#include<conio.h>
void main()
{
char line[80];
clrscr();
printf Enter a linen ;
scanf %s ,line);
printf The entered line is:%s ,line);
getch();
}
Reading and writing strings : Program

Every C compiler provides a large set of string handling library functions,
which are contained in the header file string.h
The following table shows some of the functions available in string.h
header file.
String handling Functions: string.h
Function Meaning
strcat() String concatenate. Append one string to another. First
character of string2 overwrites null character of string1.
strlen() Returns the length of the string not counting the null
character.
strlwr() Converts a string to lower case.
strupr() Converts a string to upper case.
strcpy() Copies a string into another.
strcmp() Compares two strings
strrev() Reverses a string

The strcat() function concatenates the source string at the end of the
target string. For example Computing and Techniques on
concatenation would result in string ComputingTechniques .
The general form is
strcat(string1, string2);
strong2 appends to string1 and the first character to string2 overwrites
null character of first string1.This function returns the first argument
i.e., string1. The string2 remains unchanged.
strcat() function

Program
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char s1[30],s2[15];
clrscr();
printf Enter String : ;
gets(s1);
printf Enter String : ;
gets(s2);
printf The entire string is:%s ,strcat(s1,s2));
getch();
}
strcat() function : Program
Output
Enter String1:Jiffy
Enter String2:Solutions
The entire string is:
Jiffy Solutions

strcmp() function compares two strings to find out whether they
are same or different.
The two strings are compared character by character until there
is a mismatch or end of one of the strings is reached, whichever
occurs first.
The general form is:
strcmp(string1, string2);
If the two strings are same, strcmp() returns a value 0.
If they are not same, it returns the numeric difference between
the ASCII values of the first non-matching characters.
That is, it returns less than 0 if string1 is less than string2, and
greater than 0 if string1 is greater than string2.
strcmp() function

Program
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char s1[25],s2[25];
int c;
clrscr();
printf Enter string : ;
gets(s1);
printf Enter string : ;
gets(s2);
c=strcmp(s1,s2);
if(c>0)
printf String > String ;
else if(c<0)
printf String > String ;
else
printf Both are equal ;
getch();
}
strcmp() function : Program
Output
Enter String1:abc
Enter String2:ABC
String1 > String2

strcpy(String1, String2);
The strcpy() function is used to copy the character string from String2 to
String1.
This function returns the result string String1 the String2 remains
unchanged. String2 may be a character array or a string constant.
strcpy() function

Program
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char s1[15],s2[15];
clrscr();
printf Enter String :
gets(s1);
printf The String is:%s ,strcpy(s2,s1));
getch();
}
strcpy() function : Program
Output
Enter String1:Millennium
The String2 is:Millennium

This function strlen() counts the number of characters
present in a string. The counting ends at the first null
character.
The general form is
strlen (String1);
The strlen() function returns the length of the argument
String1 excluding the null character. The argument may be
a string constant.
strlen() function

Program
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char str[30];
clrscr();
printf Enter a string: ;
gets(str);
printf The length of a string
is:%d ,strlen(str));
getch();
}
strlen() function : Program
Output
Enter a string:
Millennium Software
Solutions
The length of a string
is:29

The strupr() function is used to convert the string
into upper case.
The strlwr() function is used to convert the string
into lower case.
The strrev() function prints the entire string in
reverse order.
strupr(), strlwr(), strrev() functions

Program
#include<stdio.h>
#include<conio.h>
#include<string.h>
void main()
{
char str[15];
clrscr();
gets(str);
printf The upper case string is:%s ,strupr(str));
printf nThe lower case string is:%s ,strlwr(str));
printf nThe reverse string is:%s ,strrev(str));
getch();
}
strupr(), strlwr(), strrev() functions : Program
Output
Enter a string:millennium
The upper case string
is:MILLENNIUM
The lower case string
is:millennium
The reverse string
is:muinnellim

Functions are building blocks of C. Function performs the same set of instructions
on different sets of data or at different portions of a program.
C functions can be classified into two categories, namely
library functions and user-defined functions.
main is an example of user-defined functions. printf and scanf belong to the
category of library functions.
The main distinction between these two categories is that library functions are not
required to be written by us whereas a user-defined function has to be developed
by the user at the time of writing a program.
The general form of C function is
Return-type Function-name (parameter list)
parameter declaration;
{
Body of function;
}
Functions

It facilitates top-down modular programming. In this
programming style, the high level logic of the overall problem is
solved first while the details of each lower-level function are
addressed later.
The length of a source program can be reduced by using functions at
appropriate places. This factor is particularly critical with
microcomputers where memory space is limited.
Many other programs may use a function. This means that a C
programmer can build on what others have already done, instead
of starting over, from scratch.
As mentioned earlier, it is easy to locate and isolate a faulty function for
further investigations.
Advantages of user-defined functions:

A function, depending on whether arguments are
present or not and whether a value is returned or
not, may belong to one of the following categories:
Category 1: Functions with no arguments and no
return values.
Category 2: Functions with arguments and no
return values.
Category 3: Functions with arguments and return
values.
Category of functions

Program
#include<stdio.h>
#include<conio.h>
Function Declaration
void printline(); void main()
{
clrscr();
printline(); /*Function Declaration*/
printf This illustrates the use of C functionsn ;
printline();
getch();
}
void printline() /*ReturnType & Function Name*/
{
int i;
for(i=1;i<=40;i++)
printf - ;
printf n ;
}
Functions with no arguments and no return values

Program
#include<stdio.h>
#include<conio.h>
void swap(int,int);
void main()
{
int a,b;
clrscr();
printf Enter numbers: ;
scanf %d%d ,&a,&b);
swap(a,b); /* Function Call*/
getch();
}
void swap(int x, int y) /*Called Function*/
{
int z;
z = x;
x = y;
y = z;
printf nAfter swapping:%d,%d ,x,y);
}
Arguments but no Return values

Program
#include<stdio.h>
#include<conio.h>
int big(int,int);
void main()
{
int a,b,max;
clrscr();
scanf %d%d ,&a,&b);
max = big(a,b);
printf nThe biggest number is:%d ,max);
getch();
}
int big(int x, int y)
{
if(x>y)
return x;
else
return y;
}
Arguments with Return Values

Recursion is a technique to be used to call itself.
In C, it is possible for the functions to call
themselves.
A function is called recursive if a statement with in
the body of a function calls the same function itself.
Program
#include<stdio.h>
#include<conio.h>
long int fact(int);
void main()
{
int n;
long int res;
clrscr();
printf Enter a positive number: ;
scanf %d ,&n);
res = fact(n);
printf The factorial is:%ld ,res);
getch();
}
Recursion
long int fact(int n)
{
long int f;
if(n==1)
return 1;
else
f = n*fact(n-1);
return f;
}

All C programs must contain atleast one function. [The main() function
serves this rule]
A function can return only one value.Thus we should not specify two
values to return.
The return type in function declaration is optional. If no return type is
specified it is assumed to be an integer which is default.
When a function is not returning any value, void type can be used as
return type.
Parameter list is optional.
C provides a statement return
return expression
Return statement is used in function definition to communicate the
return value to the calling function.
Important points about functions

Return statement indicates exit from the function and return to the point
from where the function was invoked.
There may be any number of return statements in function definition,
but only one return statement will activate in a function call.
The variable declarations within the function (between braces { }) are
local to the function and are not available outside the function.
If there is no return statement, the program will return to the calling
point after it reaches the end of the function body (}).
A function call can be used wherever a variable of same type is used
(except the left side of an assignment statement).
There should be one to one correspondence between the actual and
formal parameters in type, order and number.
C allows recursion. That is a function can call itself.
A C function cannot be defined in another function.
Important points (Contd…)

Like the values of simple variables, it is also possible to pass the values of
an array to a function.
To pass an array to a called function, it is sufficient to list the name of the
array, without any subscripts, and the size of the array as arguments. For
example, the call
largest(a,n);
will pass all the elements contained in the array a of size n. The called
function expecting this call must be appropriately defined. The largest
function header might look like:
int largest(array,size);
int array[];
int size;
Functions with Arrays

There are three basic places in a C program
where variables will be declared:
inside the function,
in the definition of function parameters,
or outside of all functions.
These variables are called local variables, formal
parameters, and global variables respectively.
Variables

The body of any function comprises of two parts:
declaration of variables and a set of executable
statements.
Variables declared inside a function are called local
variables. This name derives from the fact that a
variable inside a function can be used only inside
that function.
An attempt on our part or access the local variable
of one function in another, will draw an error from
the compiler: Identifier undefined.
Local Variables

C program consists of three sections
namely: the preprocessor directives,
the global variable section and finally
the functions.
The variables that are declared in the
global variable section are called global
variables.
While a local variable can be used only
inside a function in which it is declared,
a global variable can be used anywhere
in the program.
Global Variables Block Variables
Yet another place to declare
variables is inside any block:
these variables are called block
variables and these can be used
only inside that block.

The storage class of a variable dictates how, when
and where storage will be allocated for the
variable. The different storage classes available
are:
1. Auto
2. Register
3. Extern
4. Static
Storage classes

Automatic variables are declared inside a function in which they are to be
utilized.They are created when the function is called and destroyed
automatically when the function is exited, hence the name automatic.
Automatic variables are therefore private (or local) to the function in which
they are declared. Because of this property, automatic variables are also
refereed to as local or internal variables.
A variable declared inside a function without storage class specification is,
by default, an automatic variable.
One important feature of automatic variables is that their value cannot be
changed accidentally by what happens in some other function in the
program. This assures that we may declare and use the same variable name
in different functions in the same program without causing any confusion to
the compiler.
Auto

#include<stdio.h>
#include<conio.h>
void function1();
void function2();
void main()
{
int m = 1000;
clrscr();
function2();
printf %dn ,m);
getch();
}
Auto : Program
void function1()
{
int m = 10;
printf %dn ,m);
}
void function2()
{
int m = 100;
function1();
printf %dn ,m);
}

It is possible for use to attribute the register storage class to certain
variables.
We can tell the compiler that a variable should be kept in one of the
machine s registers, instead of keeping in the memory where normal
variables are stored).
Since a register access is much faster than a memory access, keeping the
frequently accessed variables in the register will lead to faster execution of
programs. This is done as follows:
register int count;
The important point while using register variables is, registers of CPU do
not have addresses. Thus, we should not refer the address of a register
variable.
For example,
The following statement will result an error :
register int i;
scanf %d ,&i);
Register

#include<stdio.h>
#include<conio.h>
void main()
{
register int count;
int sum;
clrscr();
for(count=0;count<10;count++)
sum = sum + count;
printf The sum is:%d ,sum);
getch();
}
Register : Program

This is the default storage class for all global variables.
Extern storage class variables get initialized (to zero in the
case of integers) automatically, retain their value
throughout the execution of the program and can be
shared by different modules of the same program.
(owever, assuming int intvar; is present in a.c., to be also
to have proper binding with the same variable, b.c
another file should have extern int intvar .
Extern

a.c file
#include<stdio.h>
#include<conio.h>
int intvar;
extern float f;
void main()
{
char ch;
funct(ch,intvar);
printf %f ,f);
getch();
}
Extern : Program
b.c file
float f = 84.237;
extern int intvar;
funct(char c, int intvar)
{
char c1,c2;
:
:
}

The static storage class has a number of implications depending upon its
usage.
The default storage class for all local variables is auto. This can be
changed to static by prefixing the declaration with the keyword static as
in
static int intvar.
A local variable with static storage class is still a local variable as far as its
scope is concerned, it is still available only inside the function in which it is
declared. But certain other properties of the variable change; It gets
initialized to zero automatically, is initialized only once, (during program
startup) and it retains its value throughout the execution of the program.
When applied to a global variable, the global variable becomes
inaccessible outside the file in which it is declared.
This storage class can be applied to functions too. Similar to case 2, the
functions become inaccessible outside the file.
Static

Program:
#include<stdio.h>
#include<conio.h>
void main()
{
function1( );
function1( );
function1( );
getch();
}
void function1()
{
static int n;
n++;
printf nThe value of n is:%d ,n);
}
Static : Program
Output
The value of n is 1
The value of n is 2
The value of n is 3

Storage
class
Type Default
initial
value
Where
declared
Scope Life Storage
Auto
or
none
Local garbage
value
within the function within the function
where it is declared
until function is no
longer active
Memory
Register Local garbage
value
within the function within the function
until function is no
longer active
CPU
registers
Static Local Zero within the function within the function
until program
ends, value of the
variable persists
between different
function calls
Memory
Extern Global Zero A heat of all
functions within a
file
All files including
other files where
declared extern
While any of these
files are active.
That is, as long as
the program’s
execution doesn’t
come to an end
Memory

A structure is a convenient tool for
handling a group of logically related
data items. These fields are called
structure elements or members.
Declaring A Structure
The general form of a structure
declaration statement is given below:
struct <structure name>
{
structure element1;
structure element2;
structure element3;
……….
……….
}
Structures
Example:
struct book
{
char name[20];
char author[15];
int pages;
float price;
}

The closing brace in the structure type declaration must be
followed by a semicolon.
It is important to understand that a structure type
declaration does not tell the compiler to reserve any
space in memory. All a structure declaration does
is, it defines the form of the structure.
Usually structure type declaration appears at the top of the
source code file, before any variables or functions are
defined.
Important points while declaring a structure type:

We can assign values to the members of a structure in a number of ways.
As mentioned earlier, the members themselves are not variables. They
should be linked to the structure variables in order to make them
meaningful members. The link between a member and a variable is
established using the member operator . Which is also known as dot
operator or period operator .
The general form is
Structure-Variable. Structure-Member;
For example,
book1.price;
We can also use scanf to give the values through the keyboard.
scanf %s ,book .name ;
scanf %d ,&book .pages ;
are valid input statements.
ACCESSING STRUCTURES ELEMENTS

we may declare an array of structures, each element of the array
representing a structure variable. For example,
struct class student[100];
defines an array called student, that consists of 100 elements. Each
element is defined to be of the type struct class. Consider the following
declaration:
struct marks
{
int sub1;
int sub2;
int sub3;
}s[5];
ARRAYS OF STRUCTURES

C permits the use of arrays as structure members.
We have already used arrays of characters inside a
structure. Similarly, we can use single-or multi-
dimensional arrays of type int or float.
For example, the following structure declaration is
valid:
struct marks
{
int number;
float sub[3];
}s[2];
ARRAYS WITHIN STRUCTURES

Structures within a structure means
nesting of structures. Nesting of
structures is permitted in C. Let us
consider the following structure
definition:
struct salary
{
char name[20];
char dept[10];
struct
{
int dearness;
int house_rent;
int city;
}allowance;
}employee;
STRUCTURES WITHIN STRUCTURES
The salary structure contains a
member named allowance which itself
is a structure with three members.
The members contained in the inner
structure namely dearness,
house_rent, and city can be referred to
as
employee.allowance.dearness
employee.allowance.house_rent
employee.allowance.city

Unions are a concept borrowed from structures and therefore follow the
same syntax as structures. However, there is major distinction between
them in terms of storage. In structures, each member has its own storage
location, whereas all the members of a union use the same location. This
implies that, although a union may contain many members of different
types, it can handle only one member at a time. Like structures, a union
can be declared using the keyword union as follows:
union item
{
int m;
float x;
char c;
}code;
UNIONS

We normally use structures, unions, and arrays to create variables of large
sizes. The actual size of these variables in terms of bytes may change
from machine to machine. We may use the unary operator sizeof to tell
us the size of a structure (or any variable).
The expression
sizeof(struct x)
will evaluate the number of bytes required to hold all the members of the
structure x. If y is a simple structure variable of type struct x, then the
expression
sizeof(y)
would also give the same answer.
SIZE OF STRUCTURES

Pointers are another important feature of C language. They are a
powerful tool and handy to use once they are mastered. There are a
number of reasons for using pointers.
A pointer enables us to access a variable that is defined outside the
function.
Pointers are more efficient in handling the data tables.
Pointers reduce the length and complexity of a program.
They increase the execution speed.
The use of a pointer array to character strings results in saving of data
storage space in memory.
Pointers

The actual location of a variable in the memory is system
dependent and therefore, the address of a variable is not known
to us immediately. We can determine the address of the variable
with the help of the operator & in C. We have already seen the use
of this address operator in the scanf function. The operator &
immediately preceding a variable returns the address of the
variable associated with it.
For example,
p = &quantity;
would assign the address to the variable p. The & operator can be
remembered as address of .
ACCESSING THE ADDRESS OF A VARIABLE

#include<stdio.h>
#include<conio.h>
void main()
{
char a;
int x;
float p, q;
clrscr();
a = A ;
x = 125;
p = 10.25, q = 18.76;
printf %c is stored at address %u , a, &a ;
printf n%d is stored at address %u , x, &x ;
printf n%f is stored at address %u , p, &p ;
printf n%f is stored at address %u , q, &q ;
getch();
}
ACCESSING ADDRESSES OF VARIABLES : PROGRAM

In C, every variable must be declared for its
type. Since pointer variables contain
addresses that belong to a separate data
type, they must be declared as pointers
before we use them.
The declaration of a pointer variable takes
the following form:
datatype *pt_name;
This tells the compiler three things about
the variable pt_name.
The asterisk (*) tells the variable
pt_name is a pointer variable.
pt_name needs a memory location.
pt_name points to a variable of type
datatype.
DECLARING POINTERS
For example,
int *p;
declares the variable p as a pointer
variable that points to an integer data
type.
Remember that the type int refers to
the data type of the variable being
pointed to by p and not the type of the
value of the pointer.
Similarly, the statement
float *x;
declares x as a pointer to a floating
point variable.

Once a pointer variable has been
declared, it can be made to point to a
variable using an assignment
statement such as
p = &quantity;
which causes p to point to quantity.
That is, p now contains the address of
quantity.
This is known as pointer initialization.
Before a pointer is initialized, it should
not be used.
INITIALIZING POINTERS
A pointer variable can be
initialized in its declaration itself.
For example,
int x, *p=&x;
is perfectly valid. It declares x as
an integer variable and p as a
pointer variable and then
initializes p to the address of x.
Note carefully that this is an
initialization of p, not *p. And
also remember that the target
variable x is declared first. The
statement
int *p=&x, x;
is not valid.

Once a pointer has been assigned the address of a
variable, the question remains as to how to access
the value of the variable using the pointer. This is
done by using another unary operator * (asterisk),
usually known as the indirection operator.
Consider the following statements:
int quantity, *p, n;
quantity = 179;
p = &quantity;
n = *p;
ACCESSING A VARIABLE THROUGH ITS POINTER

The first line declares quantity and n as integer variables and p as
a pointer variable pointing to an integer.
The second line assigns the value 179 to quantity.
The third line assigns the address of quantity to the pointer
variable p.
The fourth line contains the indirection operator *. When the
operator * is placed before a pointer variable in an expression,
the pointer returns the value of the variable of which the pointer
value is the address.
In this case, *p returns the value of the variable quantity,
because p is the address of quantity. The * can be remembered
as value of address . Thus the value of n would be 179.
ACCESSINGA VARIABLETHROUGHITS POINTER
(CONTD…)

When an array is declared, the
compiler allocates a base address and
sufficient amount of storage to contain
all the elements of the array in
contiguous memory locations.
The base address is the location of the
first element (index 0) of the array. The
compiler also defines the array name
as a constant pointer to the first
element.
POINTERS AND ARRAYS
If we declare p as an integer pointer,
then we can make the pointer p to
point to the array x by the following
assignment:
p = x;
This is equivalent to
p = &x[0];
When handling arrays, instead of
using array indexing, we can use
pointers to access array elements.
Note that *(p+3) gives the value of
x[3]. The pointer accessing method is
much faster than array indexing.

C language requires the number of elements in an
array to be specified at compile time. But we may
not be able to do so always. Our initial judgment of
size, if it is wrong, may cause failure of the program
or wastage of memory space.
Many languages permit a programmer to
specify an array s size at run time. The process of
allocating memory at run time is known as dynamic
memory allocation.
In C language there are four library routines
known as memory management functions that
can be used for allocating and freeing memory
during program execution.
DYNAMIC MEMORY ALLOCATION

Memory Allocation Functions
Function Task
malloc Allocates requested size of bytes and returns a pointer to the first byte
of the allocated space.
calloc Allocates space for an array of elements, initializes them to zero and then
returns a pointer to the memory.
Free Frees previously allocated space.
realloc Modifies the size of previously allocated space.

A block of memory may be allocated
using the function malloc. The malloc
function reserves a block of memory
of specified size and returns a pointer
of type void. This means that we can
assign it to any type of pointer.
It takes the following form:
ptr = (datatype *)malloc(byte-size);
ptr is a pointer of type datatype. The
malloc returns a pointer (of datatype)
to an area of memory with size byte-
size.
Example:
x = (int *) malloc (sizeof(int) * n);
Allocating a Block of Memory
Use of malloc Function
#include<stdio.h>
#include<conio.h>
void main()
{
int *p, n, i;
clrscr();
printf Enter n value: ;
scanf %d ,&n);
p = (int) malloc(sizeof(int)*n);
printf nEnter %d numbers: ,n ;
for(i=0;i<n;i++)
scanf %d ,* p+i));
printf nThe numbers are: ;
for(i=0;i<n;i++)
printf n%d ,* p+i));
getch();
}

calloc is another memory allocation function that is normally used for
requesting memory space at run time for storing derived data types such as
arrays and structures.
While malloc allocates a single block of storage space, calloc allocates
multiple blocks of storage, each of the same size, and then sets all bytes to
zero.
The general form of calloc is:
ptr = (datatype *) calloc (n,elem-size);
The above statement allocates contiguous space for n blocks, each of size
elem-size bytes. All bytes are initialized to zero and a pointer to the first byte
of the allocated region is returned. If there is not enough space, a NULL
pointer is returned.
Allocating Multiple Blocks of Memory

Compile-time storage of a variable is allocated and
released by the system in accordance with its
storage class.
With the dynamic run-time allocation, it is our
responsibility to release the space when it is not
required.
The release of storage space becomes important
when the storage is limited. We may release that
block of memory for future use, using the free
function:
free(ptr);
ptr is a pointer to a memory block which has
already been created by malloc or calloc.
Releasing the Used Space

It is likely that we discover later, the previously allocated memory is not
sufficient and we need additional space for more elements.
It is also possible that the memory allocated is much larger than
necessary and we want to reduce it.
In both the cases, we can change the memory size already allocated
with the help of the function realloc. This process is called the
reallocation of memory. For example, if the original allocation is done by
the statement
ptr = malloc(size);
then reallocation of space may be done by the statement
ptr = realloc(ptr, newsize);
Altering the Size of a Block

We know that a string is an array of
characters, terminated with a null
character.
Like in one-dimensional arrays, we can
use a pointer to access the individual
characters in a string.
POINTERS AND CHARACTER STRINGS
Program
#include<stdio.h>
#include<conio.h>
void main()
{
char *str;
int i=0;
clrscr();
gets(str);
while(*str!=
{
i++;
str++;
}
printf nThe length is:%d ,i);
getch();
}

In functions we can pass the duplicate
values for the actual parameters, but
we can pass the address of a variable as
an argument to a function in the
normal fashion.
When we pass addresses to a function,
the parameters receiving the addresses
should be pointers. The process of
calling a function using pointers to pass
the addresses of variable is known as
call by address.
POINTERS AND FUNCTIONS
Program : Pointers as function Parameters
#include<stdio.h>
#include<conio.h>
void main()
{
int a,b;
clrscr();
scanf %d %d ,&a,&b);
printf nBefore exchange: a=%d, b=%d ,a, b);
swap(&a,&b);
printf nAfter exchange: a=%d, b=%d ,a, b);
getch();
}
void swap(int *x, int *y)
{
int z;
z = *x;
*x = *y;
*y = z;
}

We know that the name of an array stands for
the address of its zeroth element. The same
thing is true of the names of arrays of structure
variables.
Suppose product is an array variable of struct
type. The name product represents the
address of its zeroth element.
Consider the following declaration:
struct inventory
{
char name[30];
int number;
} product[3], *ptr;
POINTERS AND STRUCTURES
Program: Pointers to Structure variables
#include<stdio.h>
#include<conio.h>
struct invent
{
char name[20] ;
int number;
}product[3], *ptr;
void main()
{
clrscr();
printf )NPUTnn ;
printf Enter name and number records : ;
for(ptr = product;ptr<product+3;ptr++)
scanf %s %d ,ptr->name,&ptr->number);
printf nnOUTPUT ;
for(ptr = product;ptr<product+3;ptr++)
printf n%st%d ,ptr->name,ptr->number);
getch();
}

A file is a place on the disk where a group of related data is
stored. Like most other languages, C supports a number of
functions that have the ability to perform basic file
operations, which include:
Naming a file,
Opening a file,
Reading data from a file,
Writing data to a file, and
Closing a file.
File Management in C

High level I/O functions
Function Name Operation
fopen() Creates a new file for use
Opens an existing file for use.
fclose() Closes a file which has been opened for use.
Getc() Reads a character from a file.
putc() Writes a character to a file.
fprintf() Writes a set of data values to a file.
fscanf() Reads a set of data values from a file.
getw() Reads an integer from a file.
putw() Writes an integer to file.
fseek() Sets the position to a desired point in the file
Ftell() Gives the current position in the file
rewind() Sets the position to the beginning of the file.

If we want to store data in a file in the secondary
memory, we must specify certain things about the file,
to the operating system. They include:
Filename.
Data Structure.
Purpose.
Following is the general format for declaring
and opening a file:
FILE *fp;
fp = fopen filename , mode ;
DEFINING AND OPENING A FILE

The first statement declares the variable fp as a pointer to the data type
FILE . As stated earlier, FILE is a structure that is defined in the I/O library.
The second statement opens the file named filename and assigns as
identifier to the FILE the pointer fp. This pointer which contains all the
information about the file is subsequently used as a communication link
between the system and the program.
The second statement also specifies the purpose of opening this file. The
mode does this job. Mode can be one of the following:
r open the file for reading only.
w open the file for writing only.
a open the file for appending (or adding) data to it.
Note that both the filename and mode are specified as strings. They
should be enclosed in double quotation marks.
DEFINING AND OPENING A FILE (CONTD…)

When trying to open a file, one of the
following things may happen:
When the mode is writing a file with
the specified name is created if the file
does not exist.The contents are
deleted, if the file already exists.
When the purpose is appending , the
file is opened with the current contents
safe. A file with the specified name is
created if the file does not exist.
)f the purpose is reading , and if it
exists, then the file is opened with the
current contents safe; otherwise an
error occurs.
DEFINING AND OPENING A FILE (CONTD…)
Consider the following statements:
FILE *p1, *p2;
p1 = fopen data , r ;
p2 = fopen results , w ;
Many recent compilers include
additional modes of operation. They
include:
r+The existing file is opened to the
beginning for both reading and writing.
w+ Same as w except both for reading
and writing
a+ Same as a except both for reading
and writing.
We can open and use a number of files
at a time. This number however
depends on the system we use.

A file must be closed as soon as all
operations on it have been completed.
fclose(file_pointer);
CLOSING A FILE

Once a file is opened, reading out of or writing to it is accomplished using the standard
I/O routines that are listed.
The getc and putc Functions
The simplest file I/O functions are getc and putc. These are analogous to getchar and
putchar functions and handle one character at a time. Assume that a file is opened
with mode w and file pointer fp1. Then, the statement
putc(c, fp1);
writes the character contained in the character variable c to the file associated with
FILE pointer fp1. Similarly, getc is used to read a character from a file that has been
opened in read mode. For example, the statement
c = getc(fp2);
would read a character from the file whose file pointer is fp2.
The file pointer moves by one character position for every operation of getc
or putc. The getc will return an end-of-file marker EOF, when end of the file has been
reached. Therefore, the reading should be terminated when EOF is encountered.
INPUT/OUTPUT OPERATIONS ON FILES

PROGRAM
#include<stdio.h>
#include<conio.h>
void main()
{
FILE *f1;
char c;
clrscr();
printf Data )nputnn ;
f1 = fopen )NPUT , w ;
while((c=getchar()!=EOF)
putc(c,f1);
fclose(f1);
printf nDataOutputnn ;
f1 = fopen )NPUT , r ;
while((c=getc(f1))!=EOF)
printf %c ,c);
fclose(f1);
getch();
}
Program : Writing to and Reading from a File

The functions fprintf and fscanf perform I/O operations that are identical
to the familiar printf and scanf functions, except of course that they work
on files.
The first argument of these functions is a file pointer which specifies the
file to be used.
The general form of fprintf is
fprintf(fp, control string , list ;
where fp is a file pointer associated with a file that has been opened for
writing. The control string contains output specifications for the items in
the list. The list may include variables, constants and strings. Example:
fprintf f , %s %d %f ,name,age,7.5 ;
Here, name is an array variable of type char and age is int variable.
The fprintf & fscanf Functions

The general format of fscanf is
fscanf(fp, control string , list ;
This statement would cause the reading of the items in the list from the
file specified by fp, according to the specifications contained in the
control string.
Example:
fscanf f , %s %d , item, &quantity ;
Like scanf, fscanf also returns the number of items that are successfully
read. When the end of file is reached, it returns the value of EOF.
The fscanf Function

It is a parameter supplied to a program when the program
is invoked. This parameter may represent a filename the
program should process.
For example, if we want to execute a program to copy the
contents of a file named X_FILE to another one named
Y_FILE, then we may use a command line like
C:TC>PROGRAMX_FILEY_FILE
PROGRAM is the filename where the executable code of
the program is stored. This eliminates the need for the
program to request the user to enter the filenames during
execution.
COMMAND LINE ARGUMENTS

We know that every C program should have
one main function and that it marks the
beginning of the program.
But what we have not mentioned so far is that
it can also take arguments like other
functions. In fact main can take two
arguments called argc and argv and the
information contained in the command line is
passed on to the program through these
arguments, when main is called up by the
system.
The variable argc is an argument counter that
counts the number of arguments on the
command line. The argv is an argument vector
and represents an array of character pointers
that point to the command line arguments
How do these parameters get into the program?
The size of this array will be equal to the
value of argc. For instance, for the
command line given above, argc is three and
argv is array of three pointers to strings as
shown below:
argv[0] PROGRAM
argv[1] X_FILE
argv[2] Y_FILE
In order to access the command line
arguments, we must declare the main
function and its parameters as follows:
main(argc,argv);
int argc;
char *argv[];
The first parameter in the command line is
always the program name and therefore
argv[0] always represents the program
name.

#include<stdio.h>
#include<conio.h>
void main(argc,argv)
int argc;
char *argv[];
{
FILE *fp;
int i;
char word[15];
clrscr();
fp = fopen(argv[1],"w");
printf("nNo.of arguments in Command
line=%dnn",argc);
Program : Command line Arguments
for(i=2;i<argc;i++)
fprintf(fp,"%s",argv[i]);
fclose(fp);
printf("Contents of %s filenn",argv[1]);
fp=fopen(argv[1],"r");
for(i=2;i<argc;i++)
{
fscanf(fp,"%s",word);
printf("%s",word);
}
fclose(fp);
printf("nn");
for(i=0;i<argc;i++)
printf("%*sn",i*5,argv[i]);
getch();
}

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Learning c - An extensive guide to learn the C Language

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Learning c - An extensive guide to learn the C Language