Introduction to C:
C is a general-purpose,
structured programming language. Its instructions consists of terms that
resemble algebraic expression, augmented by certain English keywords such as
if, else, for, do and while, etc. C contains additional features that allow it
to be used at a lower level, thus bridging the gap between machine language and
the more conventional high level language. This flexibility allows C to be used
for system programming (e.g. for writing operating systems as well as for
applications programming such as for writing a program to solve mathematical
equation or for writing a program to bill customers). It also resembles other
high level structure programming language such as Pascal and FORTRAN.
2.1 Historical Development of C:
C was an offspring of the
‘Basic Combined Programming Language’ (BCPL) called B, developed in 1960s at Cambridge University
C was used mainly in academic environments for many
years, but eventually with the release of C compiler for commercial use and the
increasing popularity of UNIX, it began to gain populuide spread support among
compiler professionals. Today, C is running under a number of operating systems
including Ms-DOA. C was now standardized by American National Standard
Institute. Such type of C was named ANSI C.
2.2 Importance of C:
Now-a-days, the popularity of C
is increasing probably due to its many desirable qualities. It is a robust
language whose rich set of built-in functions and operators can be used of
built-in functions and operators can be used to write any complex program. The
C compiler combines the capabilities of an assemble language with the features
of a high-level language and therefore it well suited for writing both system
software and business packages. In fact, many of the C compilers available in
the market are written in C.
Programs written in C are efficient and fast. This is
due to its variety of data types and powerful operators. It is many times
faster than BASIC (Beginners All Purpose Symbolic Instruction Code – a high
level programming language). There are only 32 keywords and its strength lies
in its built-in functions. Several standard functions are available which can
be used for developing programs. C is highly portable. This means that C
programs written for one computer can be seen on another with little or no
modification. Portability is important if we plan to use a new computer with a different
operating system. C Language is well suited for structure programming thus
requiring the user to think of a problem in terms of function modules or
blocks. A proper collection of these modules would make a complete program.
This modular structure makes program debugging, testing and maintenance.
Another important feature of C is its ability to
extend itself. A C program is basically a collection of functions that are
supported by the C library. We can continuously add our own function to the C
library. With the availability of a large number of functions, the programming
task becomes simple.
2.3 Basic Structure of C programs:
Every C program consists one or more modules called
function. One of the function must be called main( ).A function is a
sub-routine that may include one or more statements designed to perform a
specific task. A C program may contain one or more sections shown in figure:
 |
|||
The documentation section consists of a set of comment lines giving the name of the program, the author and other details which the programmer would like to use later. The link section provides instructions to the compiler to link function from the system library. The definition defines all the symbolic constants. There are some variables that are used in more than one function. Such variables are called global variables and are declared in global declaration section that is outside of all the function. Every C program must have one main( ) function section. This section consists two parts: declaration part and executable part. The declaration part declares all the variables used in the executable part. These two parts must appear between the opening and the closing braces. The program execution begins at the opening braces and ends at the closing brace. The closing brace of the main ( ) function section is the logical end of the program. All the statements in the declaration and executable parts ends with a semicolon. The subprogram section contains all the user-defined functions that are called in the main ( ) function. User-defined functions are generally placed immediately after the main ( ) function, although they may appear in any order. All section, except the main ( ) function section may be absent when they are not required.
2.4 Executing a C Program
Executing a program written in C involves a series of
steps:
1. Creating the program;
2. Compiling the program;
3. Linking the program with functions that are needed
from the C library; and
4. Executing the program.
The program can be created using any word processing
software in non-document mode. The file name should end with the characters
“.c” like program .c, lab1.c, etc. Then the command under Ms DOS operating
system would load the program stored in the file program .c i.e.
(User-defined Functions)
MSC pay .C
And generate the object code. This code is stored in
another file under name ‘program.obj’.
In case any language errors are found, the compilation is not completed. The
program should then be corrected and compiled again. The linking is done by the
command LINK program.obj which
generates the executable code with the filename program.exe. Now the command .program
would execute the program and give the results.
/* First
Program written in C */
/* Save it as hello.c */
#
include <stdio.h> /* header file */
Void main
( ) /* main ( ) function */
{
Print
(“hello, world in”); /* statement */v
}
Output:
hello, world
/* Program to
calculate the area of a circle */
/*
area.c */
#
include <stdio.h> /* library file access */
Void main(
) /* function heading */
{
float
radius, area; /* variable decleration */
printf
(“Enter radious?=”) /* output statement */
scanf
(“%f”, & radius); /* input statement */
area =
3.14159 * radius; /* assignment statement */
printf
(“Area=%f”, area); /* output statement */
}
Comments
Post a Comment