Unit
2. Introduction to c
# C-Programming :-
·
C is very robust machine
independent, general purpose, concise programming language.
·
C-Programming language was at
first developed by Dennis Ritchie at AT & T Bell Labs, USA in 1972.
·
Famous operating system such as
UNIX, LINUX, MINIX and many system and application program are written in c.
·
C consist of very few number of
keywords (reserved words) in comparison to other programming languages.
·
C is general purpose
programming languages which features economy of expressions, modern control
flow, and data structure a rich set of operators.
·
C is typical programming
language for academic process.
2.1 History of C program :-
1.
By 1960, FORTRAN (Formula
Translation) and COBOL( Common Business Oriented Language) were developed with
specific use and specific purposes.
2. In 1960, a committee was developed ALGOL (Algorithmic Oriented
Language). But it was too abstract and general.
3. In 1963, Cambridge University developed CPL (Combined Programming
Language). But it was too big has too many feature.
4. In 1967, Martin Richards (at Cambridge University) developed BCPL.
But it become less powerful and too much specific.
5. In 1970, Ken Thompson developed a programming language B. But it was too,
like other programming language.
6. Taking all the good points of BCPL, CPL and B programming language was
developed in 1972 bu Dennis Ritchie at AT and T Bell Lab, USA.
7.
2.3 Character set, Token and
Comments :-
2.3.1 character set:
A character denotes any alphabets, digits or special symbol used to
represent information. The table given below shows the valid alphabets, numbers
and special symbols allowed in c.
|
Alphabets |
Uppercase (i.e. A, B,….,Y, Z)or Lowercase (i.e. a, b,……,y, z) |
|
Digits |
0,1,2,…….,9 |
|
Special symbols |
+ - * / = () {} [] < > ‘ “ ! # %
& | ~ \ . , ; : ? |
|
White space characters |
Blank, new line, tab etc |
2.3.2. Token:
Tokens are collection of different characters, symbols, operators or
puntuators. The first job of compiler is to test the validity of these token.
There are six types of tokens as prescribed by C:
i.
Keywords
ii.
Identifiers
iii.
Constants
iv.
String constants
v.
Operators
vi.
Punctuators
Keywords:
Keywords are predefine words
that have strict meaning. For example run has meaning in English but urn is
senseless. So run can can be considered as keywords in English where as urn is
not keyword. There are 32 keywords in ANSI C.
|
auto |
double |
If |
static |
|
break |
else |
int |
struct |
|
case |
enum |
long |
switch |
|
char |
extern |
near |
typedef |
|
const |
float |
register |
union |
|
continue |
far |
return |
unsigned |
|
default |
for |
short |
void |
|
do |
goto |
signed |
while |
Basics usage of these keywords –
if, else, switch, case, default – Used for decision control programming structure.
break – Used with any loop OR switch case.
int, float, char, double, long – These are the data types and used during variable declaration.
for, while, do – types of loop structures in C.
void – One of the return type.
goto – Used for redirecting the flow of
execution.
auto, signed, const, extern, register, unsigned – defines a variable.
return – This keyword is used for returning a
value.
continue – It is generally used with for, while and
dowhile loops, when compiler encounters this statement it performs the
next iteration of the loop, skipping rest of the statements of current iteration.
enum – Set of constants.
sizeof – It is used to know the size.
struct, typedef – Both of these keywords used
in structures (Grouping of data types in a single record).
union – It is a collection of variables, which
shares the same memory location and memory storage.
Identifiers:
Identifiers can be defined
as programmer defined elements like the name of variables, functions, array,
structure etc.
Following are some valid
identifiers names:
LenghtOFBox
Length_of_box
Length2
LemGth
l
constants:
Constant are the entities
that never change. All the integer value can be considered as integer constants
(i.e. 5, 97 etc.) and all the fractional parts can be thought as floating
constants (i.e. 5.7,3.340 etc). Character are also constants which are single
alphabets enclosed by single quotes (i.e. ‘a’, ‘x’,’y’ etc.)
String constants:
1.
A string constant is a sequence of
alphanumeric characters enclosed in double quotation marks whose maximum length
is 255 characters.
2.
String constants are considered to
as array of characters and are enclosed within double quotes. So ‘a’ and “a” are
considered different.
3.
For the double quote or single
quote to be the part of the string, they should be proceded by back slash (\).
For example
|
For string |
String to be written |
|
“Ram is a boy” |
“\”Ram is a boy\”” |
|
Ram’s wife |
“Ram\’s wife” |
|
He said “ health is wealth” |
“He said \”health is wealth\”” |
Operator:
Operators are special
symbols which cause to perform mathematical or logical operations. Following
are the symbols used for arithmetic operators in C.
|
Operators |
Meaning |
|
+ |
Addition |
|
- |
Subtraction |
|
* |
Multiplication |
|
/ |
Division |
|
% |
Remainder |
A + B
Operators
Punctuators:
The special symbols which
act like punctuation marks are called punctuators. Following are the
punctuators used in C.
Parenthesis ()
Braces {}
Commas ,
Semicolons ;
2.3.2. Comments:
1. comments are the remarks or arbitrary string
written by programmer into programming codes and are written in between the
character set/* and */.
2. It is used by programmer
for documentation purpose.
3. it is non-executable part
of program.
4. It is ignored by the
compiler and user is free to write his comment within those symbol.
5. Following are some
example of writing comments on C.
/* this program calculates
area of a tringle*/
/*** test is***/
/**********************
*put your comment in
between*
*these line and boxes, we
are free*
************************/
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