/* An example on the use of functions :
               function with multiple returns       file: 5ex3.cpp
   FALL 1998
   ___________________________________
   Jacob Y. Kazakia   jyk0
   October 5, 1998
   Example 3 of week 5
   Recitation Instructor: J.Y.Kazakia
   Recitation Section  01
   ___________________________________
 
Purpose: This program uses a function  named properties
to calculate the volume and total surface of a right prizm
which has as base a n-sided regular polygon inscribed in
a circle of a given radius.
 
The function properties has the following parameters:
a)  The radius  of the base  ( in meters )
b)  The height   ( in meters )
c)  An integer m denoting the number of sides of the
    regular polygon
d)  The volume
e)  The area denoting the total surface area of the solid.
 
The first 3 arguments are inputs, the last two are ouputs.
 
Algorithm:  The length of each side of the regular polygon
is calculated by:
 
side = 2 * r * sin( pi / m )     Why?
 
The area of the base is calculated by :
 
base_area = pi * r * r * { sin(2*pi/m) / (2*pi/m) }   why?
 
               The volume is:
 
               volume = base_area * height
 
               The total surface area is:
 
               area = 2 * base_area + m * side * height
 
 
 
                */

 #include <iostream.h>
 #include <math.h>
 
  // Prototype the function
 
void properties(float radius, float height, int m, 
                float& volume, float& area);

//  Define the constant pi
 
const float PI = 3.14159265358979 ;
 
void main()
{
 
// declare the variables of the main function
 
int m ;    // integer denoting the number of sides
float r ;  // the radius
float h ; // the height of the object
 
float volume, area ;
 
//  "hard code"  the input  variables
 
r  = 2.34 ; // meters
h  = 1.12 ; // meters
m  = 9 ;

// calculate volume and area ( the output variables)
by invoking the function
 
properties( r, h, m, volume, area );

// output the variables
 
cout<<"\n\n  For the given geometry:  radius = "<< r <<"
height = "<< h;
cout<<" both in meters" << endl;
cout<<"  and for a "<< m <<"-sided solid we have volume = ";
cout << volume << " cubic meters" << endl;
cout<<"                  and total surface area = ";
cout << area << " square meters" << endl;
 
 
// hold the screen
 
cout<<" \n\n enter e (exit) to terminate the program....";
char hold;
cin>>hold;
}

 //  definition of function volume
 
void properties(float radius, float height, int m, 
                float& volume, float& area)
{
// declare the local variables
 
float pi = 3.141592654;
float side, base_area;
 
side = 2 * radius * sin(pi/m);
 
base_area = pi * radius * radius * (sin(2*pi/m)/(2*pi/m));
 
area = 2 * base_area + m * side * height;
 
volume = base_area * height;
 
// no returns here
}

/*      HERE IS THE OUTPUT
 
 
 
For the given geometry:  radius = 2.34  height = 1.12 both in meters 
and for a 9-sided solid we have volume = 17.739 cubic meters
                and total surface area = 47.8114 square meters
 
 
enter e (exit) to terminate the program....
 
 
*/