The document discusses the structure and components of a C program. It explains that a C program includes a main function, header files, comments, variables, and code blocks. Header files provide function definitions and declarations. Comments are used to understand the code and do not affect execution. The main function contains the primary code block. Local variables are only accessible within the main function block while global variables can be accessed throughout the program. The document also outlines some basic rules for writing C programs.

1. Structure
C
OF

2. // Addition of two numbers
#include<stdio.h
#include<conio.h>
Int sum;
Void main( )
{
Clrscr( );
Int a, b,;
Printf(“the 2 number is:”);
Scanf(“%d%d”,&a,&b);
Sum=a+b;
Printf(“the sum of two numbers is%d”sum);
Getch();
}
Documentation Block
Link section
Global variable
Main( ) Function
Clear the screen
Local variable
Mainfunction()Block
{
Declaration Block
Executive statement
}
User define function
block
Fun 1
Fun 2

3. 1. Comments are use to understand the section of the
program
2. What ever you have written inside the comment entry , it
may not affect the code.
3. Comment entry Two types
singe line comment- If the comment entery in a single line then
“//” symbol is used for single line comment entry
Example-// print “Hello”
Multi Line comment-If the comment entries are sveral lines or
Multiple lines then multi line comment is used.
Example-/*print the program
“Hello”*/

4. Link block
The link block provides instruction to the
compiler to link function from the system
library
Example- #include<stdio.h>
On the above program “#” is said to be
preprocessor directive and “include” is
said to be include processor directive.

5. Header file
The header file are the files that contains various
function definition , constants value and data type .
* The extension name of the header file is “.h” .
Types of header file
Stdio.h-its stands for input/output header file.
Its holds the inbult function like printf(), scanf() etc.
Conio.h- its holds the function “clrscr()” , “getch()” etc.
Math.h- its holds the some mathematical function like abs() ,
Sqrt() etc.
String.h-use for string character.

6. Main block
Every program execution can be started from mani()
function
Use of void
The keyword “void” along with the main() function
signifies that the function does not return any value.
Main function block
The block which is cover by curly bracket is known as
Main function block.
Clrscr();
It is used for clear the screen

7. Local variable
The variable which are declared or accessed only inside the
mainfunction( ) block , these type of variable are said to be
local variable
Global variable
The variable or identifier is declared on the above of the main
function( ) is known as Global variable
Declaration block
In this block we write the program and those
statement are used in write a program is known as
Executive statement
User define function
• The function is defined by the user is said to be user define function.
• In user defined function the user can creat a function as per the
requirement
• Example= array

8. Rules for writing C-Programing
1. There is a special function such as main() function should
be defined during the program.
2. Each statement should be terminated with semicolon(;).
3. Each line in a ‘c’ program that ends with a semicolon is a
statement.
4. Each statement always in lower case.
5. Blank space should not be allowed while defining the
program statement.
6. The body of main function should be placed any where of
the program.
7. We cant change the library function.
8. We have to define header file
9. All key words must be in small later.