1.1 Basic Structure of C Program in C Language

 

C Language Tutorials 

 Basic Structure of C Program 

The format of writing C program
The basic structure of a C program is very flexible
It consists of following parts:

• Preprocessor directive
• main() function
• Program body (C statements)

Example:

#include <stdio.h>

void main()

{

 printf("Hello World .");

}

Preprocessor Directive

• First line in a processor directive to include the header file stdio.h
• It gives instructions to C preprocessor
• Preprocessor is a program that modifies C source program before compilation
• Preprocessor directives starts with hash # symbol

main() Function

• main () function is the place where execution of C program starts
• When a program executes, the control enters main () function and  starts executing its Statements

 

Program Body

• Statements are written in curly braces
• The braces are also known as delimiters
• These statements are collectively known as the body of program
• Every statement program is terminated with a semi colon;

Define Preprocessor

• It is used to define a constant
• It starts with # symbol
• It is not terminated with semicolon ;

 Syntax

# define identifier value

# It indicates the start of preprocessor directive

Example

 # define PI 3.141593

 

Header Files

• It is collection of standard library functions to perform different tasks
• Standard library functions or simply C Library functions are built-in functions in C programming
• Each header file contains different types of predefined functions
• Many header files can be included in one program
• Header file must be included before calling of its function in the program
• Extension of header file is .h
• The include preprocessor directive is used to include header files in program
• These files are provided by C compiler system
• Header files are normally stored in INCLUDE subdirectory

Syntax:

# include<Header file name> or # include “header_file_name”

 

Example

# include<stdio.h>

#include<math.h>

#include<conio.h>

 

 

main() function

• main() function is the place where the execution starts
• When the program is executed, the control enters main() function and starts its execution
• Each program contains main() function
• If a program does not contains main function, it can be compiled but not executed
• Statements are written in the body of main function
• Body is enclosed in curly braces { }

Syntax

void main ()

{

Body of main function

}

 

• The definition of main function starts with keyword void
• void means that the function will return no value