STRUCTURE OF C PROGRAM:

STRUCTURE OF C PROGRAM:

Structure	Example Program
Documentation/Comment Section	/*Program to find perimeter of  a  circle */
Linkage/ Preprocessor directive /File Include Section	#include<stdio.h> #define  PI  3.1415
User defined Function / Subprogram           prototype/Declaration Section	float perimeter();
Global Declaration Section	float radius, result;
Main Function Section       Local Declaration Part       Executable Code Part	void main( ) {      float  p;      printf(“ Enter radius :  “);      scanf(“ %f ”, & radius);      p = perimeter( );      printf(“ Perimeter : %f ”, p); }
User defined Function /Sub Program Definition/Implementation Section Function 1(  )        Local Declaration Part        Executable Code Part Function 2(  ) …………… Function N(  )	float perimeter( ) {    result= 2 * PI * radius;    return (result); }

Documentation/ Comment Section: 

  

  Comments are represented with statements enclosed between /* and */. The statements specify the purpose of the program for better understanding. Any statements enclose within /* and */ are not executed by the compiler. This section is optional and if required can be used in any part of the program.

Linkage/ Preprocessor directive /File Include Section: 

  This section contains instructions which are processed before the compiler executes the program statements. There are two types of pre-processor directives namely File inclusion and Macro (constant) pre-processor directive

User defined Function / Subprogram Prototype/Declaration Section:

   This section serves the purpose of declaring user defined functions that can be used in the program.

Global Declaration Section: 

   Variables declared here for its type can be used till the end of the program and anywhere in the program.

Main Function Section:

   Every program should have a main function. Every C program execution begins from main function. The main function consists of Local Declarations and Executable statements.   For every program the above two parts should be enclosed in flower braces with { indicates the beginning of the main function and } indicates the end of the main Function.

Local variable declaration:

    Variables declared here for its type can be used only in the main( ) function.

Executable Statements:

   The statements can be an input or output or function call or assignment or return statement.    

User defined Function Implementation:

   Functions defined by the user. These are placed mostly after the main( ) function or above the main( ) function.

Tokens:

     The smallest possible individual valid units or components of a C- program are called Tokens. The Tokens in ‘C’ language are

         Key words / Reserved words, Identifiers, Constants, Operators, Strings, Comments

Comments:

•  Any set of statements enclosed within /* and */ are taken as comments.

•  These statements are not executed by the compiler.

•  These statements are given by the programmer to specify the purpose of the program or statement.

• These statements convey information for the programmer and others for proper understanding.

•  Comments are optional for a program and can be written anywhere in the program.

•  Example: /* welcome to programming */

     Key words/ Reserve words :

• These words have predefined meaning. The meaning of these words cannot be changed.

• All keywords must be written in small letters only  (except additional c99 keywords) and  no blank space allowed in keywords

• Keywords should not be used as variable / identifier names. 

• These words can be used  anywhere in the program.

• Examples: auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if,  int, long, register, return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while etc.    

Identifiers :

           It is the name given to identify a memory location(variable), function, structure, union, macro, label, array etc.,  There are two types of identifiers

Rules for declaring User defines Identifiers:

1. An identifier must consist of only alphabetic character , digits, and underscore.

2. First character must be alphabetic character or  under score and should not be a digit.

3. Second character onwards  can be alphabetic character or digit or under score.

4. Identifier name can be up to  31/63 characters depending on the system.( but the first 8 characters are  

      significant)

5. It cannot be same as  key word / reserved word.

6. May not have a white space or any other special symbol except under score.

7. An identifier defined in a C standard library should not be redefined.

8. C – language is Case-sensitive. So that, the variable name should be defined specifically to uppercase or

      lower case letters.

Examples for User defines Identifiers :

--Valid identifiers                       -- In Valid identifiers

Rollnumber, Name                           4you, Do  today,  #welcome

Subject1, marks                              auto, int      

College_name 

    

Note: Programmer should ensure that the name given for the identifier at the declaration , the same name should be used for every subsequent reference in the program.