Introduction: 1.     Overview, History, Features, Advantages and Disadvantages of C Language. 2.     Structure of C program. 3.     Compiling Process. 4.       C Preprocessor and Header Files

C Programming

Overview of C language

           C is a general-purpose, structured, procedural, compiled, high-level programming language that was originally developed by Dennis M. Ritchie at AT&T’s Bell Lab for use with the UNIX operating system by inheriting the features of B and BPCL with his own features. C was originally first implemented on the DEC PDP-11 computer in 1972. It is suitable for preparing system software as well as application software. The file extension of c program is .c.

           C is also called middle (intermediate language) level language because it combines the best features of high level language and low level language.

A Brief History of C Language

The C programming language was developed by Dennis Ritchie at Bell Labs during the early 1970's. Quite unpredictably it derived from a computer language named B and from an earlier language BCPL. Initially designed as a system programming language under UNIX it, expanded to have wide usage on many different systems. The earlier versions of C became known as K&R C after the authors of an earlier book, "The C Programming Language" by Kernighan and Ritchie. C was standardized by ANSI (American National Standard Institute) in 1980. It is still used for some system and network programming as well as for embedded systems.

Features and Importance of C:

a)      It is highly portable language: - it means C programs written for one computer can be run on another computer without little or no modifications.

b)     It is structured language: - because it has a fixed structure.

c)      It is efficient and fast: - it is efficient and fast due to its verities of data types and powerful operators.

d)     It can handle low-level activities

e)      It can be compiled on a variety of computer platforms

f)       It contains a powerful instructions set of data operators that tell computer how to manipulate the data within a program.

g)      It has both the features of high level language as well as low level language.

h)     It has rich system library: - because it has large numbers of predefined keyword and library functions.

Advantages of C

a)      It is one of the efficient and fast executing programming languages.

b)     It is easy for debugging, testing and maintaining.

c)      There is no limitation while programming using C. We can develop any kinds of program.

d)     C is powerful language and the use of pointer has made it unique.

e)      Its compiler is easily available.

f)       Length of programs can be reduced by using function.

g)      Reusability of function increases.

Disadvantages of C

a)      There is no runtime checking.

b)     There is no strict type checking.

c)      It is very difficult to fix the bugs.

d)     It is not powerful like as object oriented programming.

e)      Pointer is one of the unique features which have made C powerful but if it is mishandled the system may crash so it is risky too.

Basic structure of C program

      Here, we can easily illustrated each component of a basic structure of C program as below

·         Documentation section: - it contains a set of comments lines about the name of program, the author, algorithm, methods used and other detail. E.g. // WAP to find sum of two number.

·         Link Section: -it provides instruction to the compiler to link functions with program from the system library. E.g. #include<stdio.h>, #include<conio.h> etc.

·         Definition section: - in this section, all symbolic constants are defined. E.g. #define pi 3.147

·         Global declaration section: - In this section, declared variable as global which are used in more than one functions.

·         Main () function section: - Every C program starts and ends with a main () function. It contains declaration and executables parts where declaration part declares all the variables used in the execution part. E.g. int a=2, b=5;

a=a+2;

b=b+8;

·         Subprogram section: -This section contains all the user-defined functions that are called in the main function.

Documentation Section

Link Section

Definition Section

Global Declaration Section

Declaration part Executable part Main() function section { }

Subprogram Section Function 1 {} Function 2 {} - - Function n {} User-defined functions

Fig. Basic structure of a C program

Example

// WAP to calculate the area of circle using function.          : Documentation section

#include<stdio.h>                                : link section

#include<conio.h>

#define pi 3.147                                  : definition section

float r;                                                                                     :global declaration section

float area(float x);

void main()                                          : starting from here to main function

{  float value;                                       :declaration part

clrscr();

printf("Enter a radius of circle\t");

scanf("%f",&r);

value=area(r);             :executable part and also calling user defined function

printf("\nArea of cirlce is: %f",value);

getch();

}

float area(float x)                               :user defined function

{

return(pi*x*x);

}

Compiling process

Compilation refers to the processing of source code files (.c, .cc, or .cpp) and the creation of an 'object' file. This step doesn't create anything the user can actually run. Instead, the compiler merely produces the machine language instructions that correspond to the source code file that was compiled. In c programming compiling process consists of following steps:

v  Preprocessing: - They instruct compiler to do required pre-processing before actual compilation. You can call this phase text substitution or interpreting special preprocessor directives denoted by #.

v   Compiler – the compiler translates the high-level instructions in the .i file into low-level Assembly language instructions. The generated file containing the translation is in text format and typically has a .s file extension.

v  Assembling – the assembler converts the Assembly language text instructions in the .s file into machine code. The generated object file containing the conversion is in binary format and typically has a .o file extension.

v  Linking –Linking refers to the creation of a single executable file from multiple object files. If these piece of code need some other source file to be linked then linker link them to make it a executable file.

v  Loader: - It loads the executable code into memory. Program and data stack are created, register get initialized.

Header files and C preprocessor

Header Files:

Header files are a collection of macros, types, functions and constants. Any program that needs those functions can include the corresponding header files.

List of some commonly used Header file and their purposes:

Header Files	Purpose	Functions Declared
stdio.h	Used for standard input and output (I/O) operations.	printf(), scanf(), getchar(), putchar(), gets(), puts(), getc(), putc(), fopen, fclose(), feof()
conio.h	Contains declaration for console I/O functions.	clrscr(), exit(), getch()
ctype.h	Used for character-handling or testing characters.	isupper(), is lower, isalpha()
math.h	Declares mathematical functions and macros.	pow(), squr(), cos(), tan(), sin(), log()
stdlib.h	Used for number conversions, storage allocations.	rand(), srand()
string.h	Used for manipulating strings.	strlen(), strcpy(), strcmp(), strcat(), strlwr(), strupr(), strrev()

C Preprocessor:

The C Preprocessor is not a part of the compiler, but is a separate step in the compilation process. C Preprocessor is just a text substitution tool and it instructs the compiler to do require pre-processing before the actual compilation. All preprocessor commands begin with a hash symbol (#). 

Preprocessor directive is a collection of special statement that is executed at the beginning of a compilation process. It is placed in the source program before the main function. They all begin with the symbol # (hash) and do not require a semicolon at the end.

#define directive: it defines a text substitution, macro substitution and symbolic constant.

Syntax:

#define identifier substitution_token

For Example:

#define TRUE 1

#define FALSE

#define MAX 100

#define PI 3.14

#include directive:  -This directive searches for a header or source file, which can be processed by the implementation, to be include in the program.

Syntax:

#include <filename>

For example:

 #include<stdio.h>