Learn C Language

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hiStory
• 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 .

hiStory
• 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?
1. Many of the ideas of C language were derived and
taken from 'B' language.
2. BCPL and CPL are previous versions of 'B' language.
3. As many features came from B it was named as 'C'.

Summary of hiStory
1. B language developed by Ken Thompson
2.
Operating system developed
by C language
UNIX
3.
Developed at AT&T Bell
Laboratories
4.
Creator of Traditional C Dennis Ritchie
5.
Year 1972

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

1. 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 . , : ; ' $ "
+ - / * =

the fOrm Of a c PrOgram
• All C programs will consist of at least one function, but
it is usual (when your experience grows) to write a C
program that comprises several functions.
• The only function that has to be present is the function
called main. For more advanced programs the main
function will act as a controlling function calling other
functions in their turn to do the dirty work! The main
function is the first function that is called when your
program executes.

the fOrm Of a c PrOgram
C makes use of only 32 keywords
which combine with the formal
syntax to the form the C
programming language. Note that
all keywords are written in lower
case - C, like UNIX, uses upper
and lowercase text to mean
different things. If you are not sure
what to use then always use
lowercase text in writing your C
programs. A keyword may not be
used for any other purposes. For
example, you cannot have a
variable called auto.

The layouT of C Programs
The general form of a C program is as follows (don't worry about what
everything means at the moment - things will be explained later):
pre-processor directives
global declarations
main()
{
local variables to function main ;
statements associated with function main ;
}

f1()
{
local variables to function 1 ;
statements associated with function 1 ;
}
f2()
{
local variables to function f2 ;
statements associated with function 2 ;
}

 Note the use of the bracket set () and {}. () are used in conjunction with function
names whereas {} are used as to delimit the C statements that are associated with that
function. Also note the semicolon - yes it is there, but you might have missed it! a
semicolon (;) is used to terminate C statements. C is a free format language and long
statements can be continued, without truncation, onto the next line. The semicolon
informs the C compiler that the end of the statement has been reached. Free format
also means that you can add as many spaces as you like to improve the look of your
programs.
 A very common mistake made by everyone, who is new to the C programming
language, is to miss off the semicolon. The C compiler will concatenate the various
lines of the program together and then tries to understand them - which it will not be
able to do. The error message produced by the compiler will relate to a line of you
program which could be some distance from the initial mistake.

PreProCessor DireCTives
• C is a small language but provides the programmer with all the tools to be
able to write powerful programs. Some people don't like C because it is too
primitive! Look again at the set of keywords that comprises the C language
and see if you can find a command that allows you to print to the computer's
screen the result of, say, a simple calculation. Don't look too hard because it
doesn't exist.
• It would be very tedious, for all of us, if every time we wanted to
communicate with the computer we all had to write our own output
functions. Fortunately, we do not have to. C uses libraries of standard
functions which are included when we build our programs. For the novice C
programmer one of the many questions always asked is does a function
already exist for what I want to do? Only experience will help here but we
do include a function listing as part of this course.
• All programs you will write will need to communicate to the outside world - I
don't think I can think of a program that doesn't need to tell someone an
answer. So all our C programs will need at least one of C's standard libraries
which deals with standard inputting and outputting of data. This library is
called stdin.h and it is declared in our programs before the main function.
The .h extension indicates that this is a header file.

• All pre-processor directives begin with a # and the must start in the first
column. The commonest directive to all C programs is:
#include <stdio.h>
• Note the use of the angle brackets ($$$$ and &&&&) around the header's
name. These indicate that the header file is to be looked for on the system
disk which stores the rest of the C program application. Some text books will
show the above statement as follows:
• #include "stdio.h"
• The double quotes indicate that the current working directory should be
searched for the required header file. This will be true when you write your
own header files but the standard header files should always have the angle
brackets around them.
• NOTE: just to keep you on your toes - pre-processor statements, such as
include, DO NOT use semi-colons as delimiters! But don't forget the # must
be in the first column.

THANKYOU
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Learn C Language

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