Give the structure of 'C' programming. Also, give significance of math.h and string.h header files.

The basic structure of a C program is : 

Preprocessor directives to include libraries required for execution of the program

Declaration of global variables and macros

main() function{

                 code   ;

}

other function definitions

1. math.h is a header file that is to be include in the program if functions like sqrt(), pow(), abs() sin() etc. are to be called.

2. string.h is a header file that includes various funcitons for working on strings. These include strlen(), strcmp(), strcat(), etc.

General form of c program is...

Global declarations
int main(parameter list)
{
statement sequence
}
return-type f1(parameter list)
{
statement sequence
}
return-type f2(parameter list)
{
statement sequence
}...
return-type fN(parameter list)
{
statement sequence
}

This form is mainly concerned with Functions and Declarations.

Significance of math.h file

math.h header files drives hundreds of maths functions along with one macro. This header file returns result as double and takes double as an argument.

Significance of string.h file

string.h header file drives string related functions . This header file defines any one variable type, one macro, and number of functions.

Basically header file contains Declarations, Definitions, and Macro of related number of functions which is defined in that particular header file.

Thanks

Regards

Mahesh v Kondawar

Following is the basic structure of a C program.

Documentation Consists of comments, some description of the program, programmer name and any other useful points that can be referenced later.
Link Provides instruction to the compiler to link function from the library function.
Definition Consists of symbolic constants.
Global declaration Consists of function declaration and global variables.
main( )
{

} Every C program must have a main() function which is the starting point of the program execution.
Subprograms User defined functions.
Lets explore the sections with an example.

Write a program to print area of a circle.
In the following example we will find the area of a circle for a given radius 10cm.

Formula
The formula to compute the area of a circle is πr2 where π is PI = 3.1416 (approx.) and r is the radius of the circle.

Lets write the C code to compute the area of the circle.

#include <stdio.h>

#define PI 3.1416

float area(float r);

int main(void)
{
float r = 10;
printf("Area: %.2f", area(r));
return 0;
}

float area(float r) {
return PI * r * r;
}
The above code will give the following output.

Area: 314.16
Different sections of the above code
Documentation
This section contains a multi line comment describing the code.

In C, we can create single line comment using two forward slash // and we can create multi line comment using /* */.

Comments are ignored by the compiler and is used to write notes and document code.

Link
This section includes header file.

#include <stdio.h>
We are including the stdio.h input/output header file from the C library.

Definition
This section contains constant.

#define PI 3.1416
In the above code we have created a constant PI and assigned 3.1416 to it.

The #define is a preprocessor compiler directive which is used to create constants. We generally use uppercase letters to create constants.

The #define is not a statement and must not end with a ; semicolon.

Global declaration
This section contains function declaration.

float area(float r);
We have declared an area function which takes a floating number (i.e., number with decimal parts) as argument and returns floating number.

main( ) function
This section contains the main() function.

int main(void)
{
float r = 10;
printf("Area: %.2f", area(r));
return 0;
}
This is the main() function of the code. Inside this function we have created a floating variable r and assigned 10 to it.

Then we have called the printf() function. The first argument contains "Area: %.2f" which means we will print floating number having only 2 decimal place. In the second argument we are calling the area() function and passing the value of r to it.

Subprograms
This section contains a subprogram, an area() function that is called from the main() function.

float area(float r) {
return PI * r * r;
}
This is the definition of the area() function. It receives the value of radius in variable r and then returns the area of the circle using the following formula PI * r * r.

The math.h header defines various mathematical functions and one macro. All the functions available in this library take double as an argument and return double as the result. 

string.h is the header in the C standard library for the C programming language which contains macro definitions, constants and declarations of functions and types used not only for string handling but also various memory handling functions; 

Hi Ishwari, I am glad to see students like you who are keen to learn to programme. As we all know that c is an excellent programming language which made a platform for various other software and operating systems. To make it such a secure language header file were made, which includes several functions. The header file like math.h is responsible for doing several mathematical calculations like power calc, sqrt calc and several trigonometrical calc and string.h is accountable for doing wonders like string copy, concatenation, changing upper case letters to lower case and vice versa with strings(a combination of characters).

The syntax for including math.h and string.h is:-

#include<math.h>

#include<string.h>

Thank you. I hope this will help you. Good luck.

#include<stdio.h> //header file

main() // entry point for a program

{

// variables declaration

//logic which you want to achieve

}

math.h is a header file for working with mathmatical functions like abs() sum() etc..

string.h is also header file for working with string functions like strupr(),strlwr() etc.. 

without writing any manual code you can use these functions in your program for your purpose

ex: strlwr("nani") is automatically converted to "NANI" which is the output

Hello Ishwari
We know we have already defined data types like int, char, float, double.
Let's take int
When we declare
int i ;
It simply means an area of 2 Bytes(architecture dependent) gets allocated and the area is named as i and as our houses get some address in a street, in the same manner, this area will also have an address.

Now if we want some area which must contain say some 5 Bytes and that area has to be divided into 3 areas.
we want to give the first division to an int , the 2nd division to a char, the 3rd division to another int.
So this type of data type is not already defined.

So we need to make a data type like this on our own.

How to do that?
We use structure.

struct datatype
{
    int i;
    char c;
    int j;
};

Now if we declare
datatype x;
Then x will have our desired memory allocation.


Math.h 
has function definitions of the mathematical functions that we use.
example : pow()

Similarly, string.h has functions that we use t manipulate strings.