Thread: circle problem

Hello all,
I have tried unsuccessfully to create program using a header file, implemenation file, document file, and driver program that compute the area of a circle given only the radius. I was told to use the header file for the function header only and the implementation file for the actual code. Can someone explain to me what I did wrong. Here is the code;
header file.h

Code:

/* area.h provides an interface for a library of the area of a circle.
***************************************************************/
#include <cmath>
#include <iostream>

const double PI = 3.14159;

double radius;

double area(double radius, const double PI)
{
	return PI * pow(radius, 2);
}

implementation file.cpp

Code:

/* area.cpp converts a given radius of a circle to the area of a circle.
*  using function area() that is stored in the library area.
*
*  Input: Radius of a circle
*  Output: Area of a circle
**************************************************************/

#include <iostream>
using namespace std;
#include "area.h"
#include <cmath>

int main()
{
	double radius, area1;
	

	cout << "This program converts a given radius of a circle\n"
		 << "to the area of a circle.\n";
	cout << "\nEnter the length of your radius: ";
	cin >> radius;
	area1 = area(radius,PI);
	
	cout << "A radius length of: " << radius <<"," << "\nusing the correct equation converts to an area of: "
		 << area1 << endl;
}

driver

Code:

/*driver.cpp test the functions and constants in area.h .
*
*********************************************************/


#include<iostream>
using namespace std;
#include "area.h"
#include <cmath>

double area(double radius, const double PI);

int main()
{ 
	cout << "2 => " << area(2, PI) << "\n";
	cout << "4 => " << area(4, PI) <<"\n";
}

It works the way that I made it, however, i was told to I was told to use the header file for the function header only and the implementation file for the actual code. I am lost.

Some compilers provide M_PI, although it's non-standard.

http://www.dbforums.com/showthread.php?t=428391

Code:

#include <cmath>

const double Pi = 4.*atan(1.);

Yes, I keep forgetting that. Using gcc, it doesn't complain when I forget to put in the std::. I think I read something about the <c*> include files putting everything in both the global and std namespaces for now, or is it just gcc doing that?

I appreciate u explaining it to me. I was unsure as to why i would compile the 2 .cpp together when one is user activated by inputing a radius and the other had fixed values i didnt know that I could do that thanks again.

Originally Posted by QuestionC

Understand that the header/implementation/driver distinction is really of importance for larger programs. Headers and implementation are generally seperated for compiling efficiency.

You appear to be confused on terms. Here is a very bare-bones 3-file program which converts between temperature formats.

This is the header file.

Code:

// Header files should only contain function prototypes.
float farenheit_to_celcius (float celcius);

This is the implementation file.

Code:

#include "f2c.hpp"
// The implementation file contains the functions which are prototyped in the header.

// Convert from farenheit temperature to Celcius.
float farenheit_to_celcius (float farenheit) {
	return (farenheit - 32) * 5.0 / 9.0;
}

This is the driver.

Code:

#include <iostream>
#include "f2c.hpp"
// The driver function is the one that actually -uses- the functions prototyped in the header.

int main (void) {
	float celcius;
	float farenheit;

	std::cin >> farenheit;

	celcius = farenheit_to_celcius (farenheit);

	std::cout << celcius;

	return 0;
}

Note that we have two .cpp files which rely on each other. We have to compile them together, using this command (assuming you are using linux)

Code:

$ g++ main.cpp f2c.cpp