A language
written by Brian Kernighan and Dennis Ritchie. This was to be the language that
UNIX was written in to become the first "portable" language.
Why use C?
Mainly
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
•
A computer program is set of instructions, written in any of the computer languages, as a step by step solution of
problems.
•
Programming is the process of planning, designing,
writing, testing and maintaining these procedures or programs according to user
need.
History of C
•
In
1972 Dennis Ritchie at Bell Labs writes C and in 1978 the publication of
The C Programming Language by Kernighan & Ritchie caused a
revolution in the computing world
•
In
1983, the American National Standards Institute (ANSI) established a committee
to provide a modern, comprehensive definition of C. The resulting definition,
the ANSI standard, or "ANSI C", was completed late 1988.
•
Why C Still Useful?
•
C provides:
•
Efficiency,
high performance and high quality s/ws
•
flexibility
and power
•
many
high-level and low-level operations à middle level
•
Stability
and small size code
•
Provide
functionality through rich set of function libraries
•
Gateway
for other professional languages like C à C++ à Java
•
C is used:
•
System
software Compilers, Editors, embedded systems
•
data
compression, graphics and computational geometry, utility programs
•
databases,
operating systems, device drivers, system level routines
•
there
are zillions of lines of C legacy code
•
Also
used in application programs
Characteristics of C
- C is a Middle Level/Intermediate
Language
•
Directly access the memory through pointer
for manipulation.
•
Supports high-level programming language
syntax.
•
It has the capability to access the system's low
level functions
2. C is a Case Sensitive Language
• The
commands in ‘C’ are written in lowercase.
• The
variables written in C in upper case letters have different meaning than the
variables used in lower case letters.
3. C is a Structured Programming
Language
• It divides
the programs in small module to perform a specific task.
• Through
this approach one can have accurate, error free code.
• Each module
can have – sequence, selection or iterative statements.
4. C is Portable Language:
• C programs are run on different environment.
• E.g. if u
have written a C program in windows 95, then it can be executed in UNIX without
any or little modification
5. C is a Extendible:
• Enhance our
program with new code.
• That means
a user can write numbers of functions, subprograms according to the
requirement.
Description: This program prints the greeting “Hello,
World!” */
#include
<stdio.h>
int main ( void )
{
printf (
“Hello, World!\n” ) ;
return 0
;
}
Comment:
• A comment
is descriptive text used to help a reader of the program understand its
content.
• All
comments must begin with the characters
/* and end with the
characters */
• These are
called comment delimiters.
• The program
header comment always comes first.
• Text surrounded
by /* and */ is ignored by computer.
• Used to
describe program
Preprocessor directives
• Lines that
begin with a “ # ” are called preprocessor directives (commands).
• It tells
the computer to load contents of a certain header file.
• For
Example:
#include
<stdio.h>
#include
<stdlib.h>
#include <string.h>
•
The #include directives “paste” the contents of the
files stdio.h, stdlib.h and string.h into your source code, at the very place
where the directives appear.
•
These files contain information about some library
functions used in the program:
–
stdio
stands for “standard I/O”,
–
stdlib
stands for “standard library”,
–
string.h
includes useful string manipulation functions
The
Function Body
•
A left brace (curly bracket)
-- { --
begins
the body of every function.
•
A corresponding right brace
-- } --
ends
the function body.
The main
( ) function
•
main ( ) is always the first function called in a
program execution.
•
Every program must have a function called main.
- Here program execution begins.
•
Void indicates that the function takes no arguments.
- “void” means nothing.
•
The reserved word “int” indicates that main( )
returns an integer value.
•
The parentheses following the reserved word “main”
indicate that it is a function.
•
Braces { and } indicate a block.
•
The bodies of all functions must be contained in
braces
The
printf( ) function
printf( “Prog. In C is easy. %s \n", input );
•
printf( ) is a library function declared in
<stdio.h>
•
Syntax:
printf(
FormatString, Expr, Expr...)
•
Format String: String of
text to print.
•
Format String has
placeholders to show where to put the values.
•
Placeholders:
%s (print as string),
%c (print as char),
%d (print as integer),
%f (print as floating-point)
•
\n indicates a new line character
Expr: Values to print
printf (“Hello, World!\n”) ;
•
All statements in C end with a semi colon(;).
•
Entire line is called a statement.
•
printf() prints the text/string of characters within
double quotes (“ ”).
•
Escape character (\) indicates that printf( ) should
do something out of the ordinary.
•
return 0 ;
•
Because function main () returns an integer value,
there must be a statement that indicates what this value is.
•
The statement return 0 indicates that main ()
returns a value of zero to the operating system.
•
A value of 0 indicates that the program successfully
terminated execution
C
Syntax and Program Structure:
/* A first C Program*/
#include <stdio.h>
void main()
{
printf("Hello World \n");
}
Line
1: #include <stdio.h>
•
As part of compilation, the C compiler runs a
program called the C preprocessor. The preprocessor is able to add and remove
code from your source file.
•
In this case, the directive #include tells the
preprocessor to include code from the file stdio.h.
•
This file contains declarations for functions that
the program needs to use. A declaration for the printf function is in this
file.
Line 2:
void main ()
•
This statement declares the main function.
•
A C program can contain many functions but must
always have one main function.
•
A function is a self-contained module of code that
can accomplish some task.
•
Functions are examined later.
•
The "void" specifies the return type of
main. In this case, nothing is returned to the operating system.
Line 3: {
•
This opening bracket denotes the start of the
program.
Line 4:
printf("Hello World From About\n");
•
Printf is a function from a standard C library that is
used to print strings to the standard output, normally your screen.
•
The compiler links code from these standard
libraries to the code you have written to produce the final executable.
•
The "\n" is a special format
modifier that tells the printf to put a line feed at the end of
the line.
•
If there were another printf in this
program, its string would print on the next line.
Line 5: }
•
This
closing bracket denotes the end of the program.
Escape Sequence:
•
\n new
line
•
\t tab
•
\r carriage
return
•
\a alert
•
\\ backslash
•
\” double
quote
Anatomy
of a C Program
program
header comment
preprocessor directives
(if any)
int main ( void )
{
statement (s);
return 0
;
}
C
Character Set:
•
The C language consists of:
- Alphabets: A to
Z (Upper case) , a to z (lower case)
2. Digits: 0 to 9
3. Special Symbols: !
* : &
( ) =
# [ ]
{ } <
> ” +
- ? ’
^ ~ ;
| / .
~
Identifiers
•
Identifier is the name given to various program
elements.
•
These are user defined names that consists of
alphabets, digits and underscore,
•
Both uppercase & lowercase letters are permitted
but they cannot be used interchangeably.
e.g. 
and 
both are different variables.
Rules
for constructing an identifier:
- First
letter must be a character.
- It
should not start with a digit.
- Special
characters are not allowed.
- The
name of the identifier is so chosen that its usage & meaning becomes
clear.
- The
name of the identifier should not be same as the keyword.
Constants:
•
A constant is a quantity which does not change its
value during execution of the program.
•
The syntax for constant declaration is:
Variable:
•
Variables are memory locations in computer memory to
hold different types of data.
•
It may vary during the program execution.
•
The syntax of variable declaration is:
<datatype>
<variable name>;
- here ‘datatype’ is the type value
stored in variable ‘varname’
Keyword
•
These are the reserved words in C.
•
They have a fixed meaning.
•
The keywords are always written in lowercase.
•
There are 32 keywords in C.
•
For example:- Auto, Break, If, Else, For, Goto,
Return, Static, Union, Default, Switch, Case, Do, While, Continue, Int, Struct,
Char, Float, Long, Enum, Extern, Double, Short, Void, Const, ………….. ……..more
Data
Types
•
C programming language which has the ability to
divide the data into different types.
•
The ‘type’ of a variable determines what kind of
values it may take on.
•
Data type of an object determines the set of value
it can have & what operations can be performed on it.
Integer Data Type
•
The integer data type holds the integer value.
•
The integer number is stores in short int, int and
long int.
•
For Example
int
x; //integer variable
int
y = 454; //integer constant
short
int x1; //short integer variable
long
int y1; //long integer variable
Character Data Type
•
The character data type hold a single character.
•
It is declared by the Keyword ‘char’.
•
I/O conversion must be performed using %c conversion
code.
•
For Example:-
char
x1=‘h’; // character constant
char
x2; // character variable
Floating Point
•
The floating point data type provides the means to
store & manipulate numbers with fractional points & a very large range
of sizes.
•
The floating point number are stores in float,
double and long double.
•
For Example
float x = 2.88; //floating
point constant
float y; //floating point variable
double x1=9.8778; //floating point constant
Array Data Type
•
An array is a collection of identical data objects
which are stored in consecutive memory locations.
•
The objects are called elements of the array and are
numbered consecutively 0, 1, 2, 3, 4.....
•
These numbers are called Index values of the array
•
These numbers locate the elements position within
the array.
•
An array is used to perform the operations on a
collection of similar data items.
•
The syntax of an array is
<data
type> <array name>[size];
- Data type specifies the
data type of array.
- Array name tells the
name of array.
-
Size tells the number of elements in the array.
•
Example of Array
int
X[6];
-
It contains the array of integer data type having
the name “X” that holds the six elements
from 0 to 5.
•
Each have different integer value in it.
•
All the data elements are stored in contiguous
memory locations.
Structure
Data Type
•
The Structure is a group of different data items in
a single unit.
•
Syntax of Structure: Example
struct
<struct name> struct student
{ {
member 1;
char name[20];
member 2; int
rollno;
…………..
float marks;
} ; }
;
Union
Data Type
•
The Union is same as a Structure in C language.
•
The difference is only in the memory allocation.
•
The syntax of Union is
Union <struct
name>
{
member
1;
member
2;
…………..
}
;
String
Data Type
•
The string is a group of characters.
•
It also called an array of characters.
•
It is a sequence of characters.
•
The syntax of String is
char
string name [size];
•
For Example
char
a [10];
Operators
•
An operator is a function which is applied to values
to give a result.
•
An operand is a symbol that operates on a certain
data type.
Arithmetic
Operator
This operator perform arithmetic operations like addition, subtraction,
multiplication &so on
|
Operator
|
Meaning
|
|
+
|
Addition
|
|
-
|
Subtraction
|
|
*
|
Multiplication
|
|
/
|
Division
|
|
%
|
Module
|
Relational
Operator
•
Relational operators are used to compare their first
operand to second operand to test the validity of their relationship.
|
Operators
|
Meaning
|
Example
|
|
<
|
Less than
|
x < 5
|
|
>
|
Greater than
|
x > 2
|
|
<=
|
Less than equal to
|
x <= 4
|
|
>=
|
Greater than equal to
|
x >= 4
|
|
==
|
Equal to
|
x == 4
|
|
!=
|
Not equal to
|
x != 5
|
Logical
Operator
|
Operators
|
Meaning
|
|
&&
|
Logical
AND
|
|
||
|
Logically
OR
|
|
!
|
Logically
NOT
|
Bitwise
Operator:
|
Operators
|
Meaning
|
|
&
|
Bitwise
AND
|
|
|
|
Bitwise
OR
|
|
^
|
Bitwise
XOR
|
|
>>
|
Bitwise
right shift
|
|
<<
|
Bitwise
left shift
|
|
-
|
One’s
component
|
Conditional
Operator (?):
• It is used
to carry out conditional operations.
•
It can be used in place of if – else.
•
Syntax is:
expr1?
expr2: expr3
Condition
•
E.g. x
= (y>12) ? 2 : 400
•
If y>12 holds true, the value 2 is assigned to
variable x. else value 400 is assigned to variable x.
Assignment
Operator:
• It is used
to assign the result of an expression to a variable.
•
The most commonly used assignment operator is “=”
•
Syntax is: identifier
= expression
•
E.g. x =
5, means the value 5 is assigned to variable ‘x’.
•
x = y, in this expression the value of ‘y’ is assigned
to variable ‘x’ i.e. the value of variable on RHS is assigned to a variable on
LHS.
Expressions
•
An expression represents a single data item such as
a number or a character.
•
The expression may consist of a single entity such
as a constant, variable, an array or reference to a function.
•
Expression can also represent logical condition that
is either true or false.
•
E.g. C =
A+ B
X
= = Y
i
= i+1
Statements
•
A statement causes the computer to carry out some
action.
•
There are three different classes of statements:
- Expression Statement: It
consist of an expression followed by a semicolon (;)
e.g. a = 5; /*assignment
type statement*/
c = a+b; /*assignment
type statement*/
++i;
/*increment type statement*/
printf(“Area= %f”, area); /*function to be
evaluated*/
; /*Does
nothing. Only a semicolon*/
- Compound Statement: It
consist of several individual statements in it enclosed within a pair of
braces { }.
•
It provides a capability for embedding statements
within another statement.
e.g. { pi
= 3.142;
circumference
= 2 * pi *radius;
area
= pi *radius *radius; }
•
Above compound statement consist of three assignment
type expression statement, though it is considered in a single entity within
the program in which it appears.
3. Control Statements: These are used to create
special program features like logical tests, loops & branches.
•
E.g. while
(count < =n) {
printf(“x= ”);
scanf(“%f”, &x);
Sum + = x;
++ count; }
•
The compound statement will continue to be executed
as long as the value of count does not exceed the value of ‘n’.
•
Count increases in value during each pass through
the loop.
