history of c.ppt

Introduction
 C is a general purpose language which is very
closely associated with UNIX for which it was
developed in Bell Laboratories.
 Most of the programs of UNIX are written and run
with the help of 'C'.
 Many of the important ideas of 'c' stem are from
BCPL by Martin Richards.
 In 1972, Dennies Ritchie at Bell Laboratories wrote C
Language which caused a revolution in computing
world .
 From beginning C was intended to be useful for busy
programmers to get things done easily because C is
powerful,dominant and supple language.

Why Name 'C' was given to this
language?
 Many of the ideas of C language
were derived and taken from 'B'
language.
 BCPL and CPL are previous
versions of 'B' language.
 As many features came from B it
was named as 'C'.

ABOUT “C”
o C is a structured programming language
o C supports functions that enables easy maintainability of code, by
breaking large file into smaller modules
o Comments in C provides easy readability
o C is a powerful language.
o C programs built from
• Variable and type declarations
• Functions
• Statements
• Expressions
 C programming language - Structured and disciplined approach to
program design.

Structure Of “C” Programs
 Before going and reading the structure of C
programs we need to have a basic knowledge of
the following:
1.C's Character Set
2.C's Keywords
3.The General Structure of a 'C' Program
4.How To End A Statement
5.Free Format Language
6.Header Files & Library Functions

C's Character Set
C does not use every character set and key found
on
modern computers . The only characters that C -
Language uses for its programs are as follows:
 A-Z all alphabets
 a-z all alphabets
 0-9
 # % & ! _ {} [] () $$$$ &&&& |
 space . , : ; ' $ "
 + - / * =

 "Keywords" are words that have special
meaning to the C compiler.
 Their meaning cannot be changed at any
instance.
 Serve as basic building blocks for
program statements.
 All keywords are written in only
lowercase.
The keywords

#include<stdio.h>
#include<conio.h>
void main()
{
-- other statements
}
Basic Structure Of “C”
Programs
Header Files
Indicates
Starting of
Program
Entry Point Of
Program

 The files that are specified in the include
section is called as Header File.
 These are precompiled files that has some
functions defined in them.
 We can call those functions in our
program by supplying parameters.
 Header file is given an extension .h .
 C Source file is given an extension .c .
Header files

 This is the “Entry Point” of a program.
 When a file is executed, the start point is
the main function.
 From main function the flow goes as per
the programmers choice.
 There may or may not be other functions
written by user in a program.
 Main function is compulsory for any C
program.
Main function

 Type a program.
 Save it.
 Compile the program – This will generate an .exe file
(executable)
 Run the program (Actually the exe created out of
compilation will run and not the .c file)
 In different compiler we have different option for
compiling and running.
Running a ‘C’ Program

 The smallest individual units in a C program are known
as tokens. In a C source program, the basic element
recognized by the compiler is the "token." A token is
source-program text that the compiler does not break
down into component elements.
 C has 6 different types of tokens viz.
1. Keywords [e.g. float, int, while]
2. Identifiers [e.g. main, amount]
3. Constants [e.g. -25.6, 100]
4. Strings [e.g. “SMIT”, “year”]
5. Special Symbols [e.g. {, }, [, ] ]
6. Operators [e.g. +, -, *]
 C - programs are written using these tokens and the
general syntax.
“C” language TOKENS
Stri
ngs

Keywords in Ansi “C”
switch
typedef
union
unsigned
void
volatile
while
long
register
return
short
signed
sizeof
static
struct
int
double
else
enum
etern
float
for
goto
if
auto
break
case
char
const
continue
default
do

 They are programmer-chosen names to represent parts of
the program: variables, functions, etc.
 Cannot use C keywords as identifiers
 Must begin with alpha character or _, followed by alpha,
numeric, or _
 Upper- and lower-case characters are important (case-
sensitive)
 Must consist of only letters, digits or underscore ( _ ).
 Only first 31 characters are significant.
 Must NOT contain spaces ( ).
The Identifiers

 Constants in C are the fixed values that do
not change during the execution of a program.
Constants
CONSTANTS
Numeric constants Character constants
Integer
Constants
Real
Constants
Single
Character
Constants
String
Constants

• Integer Constants
– Refers to sequence of digits such as decimal integer, octal
integer and hexadecimal integer.
– Some of the examples are 112, 0551, 56579u, 0X2 etc.
• Real Constants
– The floating point constants such as 0.0083, -0.78, +67.89 etc.
• Single Character Constants
– A single char const contains a single character enclosed within
pair of single quotes [ ‘ ’ ]. For example, ‘8’, ‘a’ , ‘i’ etc.
• String Constants
– A string constant is a sequence of characters enclosed in double
quotes [ “ ” ]; For example, “0211”, “Stack Overflow” etc.
Constants Examples

DECLARATIONS
 Constants and variables must be declared before
they can be used.
 A constant declaration specifies the type, the
name and the value of the constant.
 any attempt to alter the value of a variable
defined
 as constant results in an error message by
the compiler
 A variable declaration specifies the type, the
name and possibly the initial value of the
variable.
 When you declare a constant or a variable, the
compiler:
 Reserves a memory location in which to store the
value of the constant or variable.
 Associates the name of the constant or variable
with the memory location.

• A Variable is a data name that is used to store any
data value.
• Variables are used to store values that can be
changed during the program execution.
• Variables in C have the same meaning as
variables in algebra. That is, they represent some
unknown, or variable, value.
x = a + b
z + 2 = 3(y - 5)
• Remember that variables in algebra are
represented by a single alphabetic character.

Variables in C may be given representations containing
multiple characters. But there are rules for these
representations.
Variable names in C :
 May only consist of letters, digits, and underscores
 May be as long as you like, but only the first 31
characters are significant
 May not begin with a number
 May not be a C reserved word (keyword)
 Should start with a letter or an underscore(_)
 Can contain letters, numbers or underscore.
 No other special characters are allowed including space.

 C is a case sensitive language.
 It matters whether an identifier, such as a
variable name, is uppercase or lowercase.
 Example:
area
Area
AREA
ArEa
are all seen as different variables by the
compiler.

 Before using a variable, you must give the compiler some
information about the variable; i.e., you must declare it.
 The declaration statement includes the data type of the
variable.
 Examples of variable declarations:
int length ;
float area ;
 Variables are not automatically initialized. For example, after
declaration
int sum;
the value of the variable sum can be anything (garbage).
 Thus, it is good practice to initialize variables when they are
declared.
 Once a value has been placed in a variable it stays there
until the program alters it.

• There are three classes of data types here::
• Primitive data types
– int, float, double, char
• Aggregate OR derived data types
– Arrays come under this category
– Arrays can contain collection of int or float or char or
double data
• User defined data types
– Structures and enum fall under this category.

Type Size Representation Minimum range Maximum range
char, signed char 8 bits ASCII -128 127
unsigned char bool 8 bits ASCII 0 255
short, signed short 16 bits 2's complement -32768 32767
unsigned short 16 bits Binary 0 65535
int, signed int 16 bits 2's complement -32768 32767
unsigned int 16 bits Binary 0 65535
long, signed long 32 bits 2's complement -2,147,483,648 2,147,483,647
unsigned long 32 bits Binary 0 4,294,967,295
float 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38
double 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38
long double 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38

/* HELLO.C -- Hello, world */
#include <stdio.h>
Void main()
{
printf("Hello, worldn");
Getch();
}
Example of “C” Program

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