Every C program is basically a group of different section that is used for different purpose. The structure gives us a basic idea of the order of the sections in a program. A well-defined structured layout makes program more readable, easy to modify, consistent format and gives better clarity and the concept of a program. Whenever we write a program in ‘C’ language, we can divide that program into six different sections. These sections are as follows:
- Documentation section
- Linkage section
- User definition section
- Global declaration section
- Main() function section
- Subprogram section
Pictorial Representation of Basic Structure of C Programming:
Figure: Basic Structure of C Program
A program in ‘C’ may not contain all the sections shown above but main() function is a must as the program execution always starts with main() .
Brief explanation of each section is given
below:
Documentation Section:
Documentation
section is generally description of program. It is only a set of comments for
program documentation. Documentation section consist program’s name, objective
of the program, author’s name and other useful details like the creation date,
title etc. that can be referenced later. It provides an overview of the program.
Example
/*
Author: Eliza Begum
Date: 2/2/2022
Description: This
program calculate simple interest
Linkage Section:
The linkage section consists of the header files that are used in the
program.
It provides instruction
to the compiler to link function from the system library. If
the programmer wants any one of the functions, from any one of the header
files, there should be a mechanism to inform the compiler. From the link section,
we instruct the compiler to link those header files from the system libraries,
which we have declared in the link section in our program.
Example:
#include<stdio.h>
#include<conio.h>
#include<string.h>
User Definition Section:
This section is used to define symbolic constants. Symbolic constants are used
for better understanding of certain names that are not going to change
throughout the program. Generally capital letter is used to define symbolic
constants. The keyword define is used in this part. Macros are used in this
section.
Example:
#define PI 3.1415
#define MAX 5
Here, PI, MAX are
symbolic constants.
Global Declaration Section:
The global variables
that can be used anywhere in the program are declared in global declaration
section. Global variables can be used by all the functions. The
user-defined functions are also declared in this part. The user defined
functions specified the functions specified as per the requirements of the
user.
Example:
int sum(int x,int y);
int a;
float b;
Main() Function Section:
The
main() function has control over the program. Every C program must have a main
function which
is the starting point of the program execution. It contains 2 parts,
namely, local variable declaration part and Executable statement part and these
two parts must be written in between opening and closing braces. Local variable
declaration part is used for declaring local variables which are to be used in
executable statement part. Executable statement contains all the instructions
to be executed.
int main()
{
int a=5; // Declaration Part
printf(“a=%d”,a); // Execution Part
return 0;
}
Sub-Program Section:
The subprogram section
contains all the user defined functions that are used to perform a specific
task. All
the function subprograms are user defined with an optional list of arguments
enclosed in parentheses and generally placed after the main() definition is
over. There can be placed in any order.
int
sum(int a, int b)
{
return
a+b;
}
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