C PROGRAMMING
FUNDAMENTALS - A REVIEW TOPICS COVERED
1. Conditional
statements
2. Control
statements
3. Functions
4. Arrays
5. Pre-processor
6. Pointers
Variation in pointer declarations
7. Function
Pointers
8. Function
with Variable number of arguments
INTRODUCTION TO C
C is a general purpose,
structured programming language. Its instructions consist of terms that
resemble algebraic expressions, augmented by certain English keywords such as
if, else, for, do and while. In this respect it resembles high level structured
programming languages such as Pascal and Fortran. C also contains additional
features, that allow it to be used at a lower level, thus bridging the gap
between machine language and high level language. This flexibility allows C to
be used for systems programming as well as for applications programming.
Therefore C is called a middle level language.
C is characterized by
the ability to write very concise source programs, due in part to the large
number of operators included within the language. It has a relatively small
instruction set, though actual implementations include extensive library
functions which enhance the basic instructions. C encourages users to create
their own library fuctions.
An important
characteristic of C is that its programs are highly portable. The reason for
this is that C relegates most computer dependent features to its library
functions. Thus, every version of C is accompanied by its own set of library
functions which are relatively standardized. Therefore most C programs can be processed
on many different computers with little or no alteration.
History of C:
C was developedDennisinRitchietheatBell1970′sTelephoneLaboratoriesby,Inc.
(now a part of AT&T). It is an outgrowth of two earlier languages, called
BCPL and B, which were also developed at Bell Laboratories.
The Combined Programming
Language(CPL) was developed at Cambridge University in 1963 with the goal
of developing a common programming language which can be used to solve
different types of problems on various hardware platforms. However it turned
out to be too complex, hard to learn and difficult to implement. Subsequently
in 1967, a subset of CPL, Basic CPL(BCPL) was developed by
Martin Richards incorporating only the essential features. However
it was not found to be sufficiently powerful. Around the same time another
subset of CPL, a language called B was developed by Ken Thompson
at Bell Labs. However it also turned out to be insufficient . Then, in 1972,
Dennis Ritchie at Bell Labs developed the C language incorporating the best
features of both BCPL and B.
C was largely confined to use within
Bell Labs until 1978, when Brian Kernighan and Ritchie published a definitive
description of the language . The Kerninghan and Ritchie description
of C is commonly referred to as ‘K &R. C’
Following the publication of ‘K&R
C’,compu desirable features, began to promote the use of C. By t become
widespread-many c compilers and interpreters had been written for computers of
all sizes
and many commercial application programs had been
developed. Moreover, many commercial software products that had originally been
written in other languages were rewritten in C in order to take advantage of
its efficiency and portability.
Early commercial implementations of C
diff original description, resulting in minor incompatibilities between
different implementations. As a
result, the American National Standards
Institute(ANSI committee X3J11) developed a standardized definition of C.
Virtually all commercial compilers and interpreters adhere to the ANSI
standard. Many provide additional features of their own.
C
and Systems Programming:
There are several features of C, which
make it suitable for systems programming. They are as follows:
a.
C is a machine independent and highly
portable language.
b.
It is easy to learn; it has only 28
keywords.
c.
It has a comprehensive set of operators
to tackle business as well as scientific applications with ease.
d.
Users can create their own functions and
add to the C library to perform a variety of tasks.
e.
C language allows the manipulation of
bits, bytes and addresses.
f.
It has a large library of functions.
g.
C operates on the same data types as the
computer, so the codes generated are fast and efficient.
Structure
of a C Program:
Every C program consists of one or more
modules called functions. One of the functions must be called main.
The program will always begin by executing the main function, which may
access other functions. The main function is normally,but not necessarily located
at the beginning of the program. The group of statements within main( ) are
executed sequentially. When the closing brace of main( ) is encountered,
program execution stops and control is returned to the operating system.
Any other function defintions must be defined
separately, either ahead or after main( ). Each function must contain:
1. A
function heading, which consists of the function name,
followed by an optional list of arguments, enclosed in parantheses.
2. A
return type written before the function name. It denotes the type
of data that the function will return to the program.
3. A
list of argument declarations, if arguments are included in the
heading.
4. A
compound statement, which comprises the remainder of the
function.
The arguments(also called parameters) are symbols
that represent information being passed between the function and other parts of
the program.
Each compound statement is enclosed
between a pair of braces{ }. The braces may contain one or more elementary
statements (called expression statements) and other compound
statements. Thus compound statements may be nested one within another. Each
expression statement must end with a semicolon(;).
Comments (remarks) may
appear anywhere within a program as long as they are enclosed within the
delimiters /* and */. Comments are used for documentation and are useful in
identifying the
program’s principal features
or in explaining
Components
of C Language:
There
are five main components of the C Language:-
1. The
character set: C uses the uppercase letters A to Z, the
lowercase letters a to z, the digits 0 to 9 and certain special
characters as building blocks to form basic program elements(e. g. constants,
variables, expressions, statements etc. ).
2. Data
Types: The C language is designed to handle five primary
data types, namely, character, integer,
float, double and void; and secondary data types like array,
pointer, structure, union and enum.
3. Constants:
A
constant is a fixed value entity that does not change its value throughout
program execution.
4. Variables:
A
variable is an entity whose value can change during program execution. They are
used for storing input data or to store values generated as a result of
processing.
5. Keywords:
Keywords
are reserved words which have been assigned specific meanings in
the C language. Keywords cannot be used as variable names.
The components of C language will be
discussed in greater detail in the following articles. This section gives only
a brief introduction to the components of C.
Example 1: The
following program reads in the radius of a circle, calculates the area and then
prints the result.
/*
program to calculate the area of a circle*/
#include<stdio.h>
/*Library file access*/
#include<conio.h>
/*Library file access*/
void main( ) /*
Function Heading*/
{
float
radius, area; /*Variable declarations*/
/*Output
Statement(prompt)*/
printf("Enter
the radius :");
/*Input
Statement*/
scanf("%f",
&radius);
/*Assignment
Statement*/
area
= 3.14159*radius*radius;
/*Output
Statement*/
printf("Area
of the circle :%f", area);
getch(
);
}
Program
output:-
Enter
the radius: 3
Area
of the circle: 28. 27431
The
following points must be considered to understand the above program:-
1. The
program is typed in lowercase. C is case sensitive i. e. uppercase and
lowercase characters are not equivalent in C. It is customary to type C
instructions in lowercase. Comments and messages(such as those printed using
printf() ) can be typed in anycase.
2. The
first line is a comment that identifies the purpose of the program.
3. The
instruction #include <stdio.h> contains a reference to a special
file called stdio. h . This file contains the definition of certain functions
required to read and print data such as printf() and scanf() . It is a header
file and hence the extension . h.
4. Similarly
#include <conio.h> links the file conio. h which is another header
file that contains the definitions of functions used for reading and printing
data at the console. The function getch() is defined in conio. h. #
denotes a preprocessor directive. More about this in a later article.
5. The
instruction void main() is a heading for the function main( ). The
keyword void denotes the return type of main and indicates that the
function does not return any value to the program after the program has
finished executing. The empty parantheses ( ) after main indicates that this
function does not include any arguments. Program execution always begins from
main( ).
6. The
remaining five lines of the program are indented and enclosed in a pair of
braces { }. These five lines comprise the compound statement within the
function main( ).
7. The
instruction float radius, area;
is a variable declaration. It establishes the symbolic
names ‘radius’asandfloating‘area’ point variables. These var numbers containing
a decimal point or an exponent.
8. The next four instructions are expression
statements. The instruction printf(“Enter
the :”);generates a request for information namely,the value for the
radius. This statement generates a prompt where the user enters the value .
9. The
value of the radius is read into (or stored in) the variable radius with
the help of the scanf ( ) function. The instruction scanf(“%f”, is&radius);usedforreadingdata.
“%f”conversionisa character which is used to accept
a floating point value.
10.The
next instruction, area = 3.14159*radius*radius; is called an assignment
statement. This instruction calculates the area by using the value of
radius entered by the user and assigns the value to the variable area.
11.
The next printf( ) statement prints the
message Area of the circle followed by the calculated area.
12.The
statement getch(); is used to pause the screen so that you can read the
output. If getch( ) is not used the screen will just flash and go away. This
function waits for the user to input some character(as it accepts a character
as input), after the program has finished executing. Any key present on the
keyboard pressed by the user is accepted by the getch function as input and its
ASCII value is returned to main( ).
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