/*
 *  ===========================================================================
 *  Compute Area of a Circle : Coefficients are defined in main program.
 *                           : Radius and area of circle are printed to screen.
 *                                                                     
 *  Copyright (C) 1998 by Mark Austin and David Chancogne.
 *                                                                     
 *  This software is provided "as is" without express or implied warranty.
 *  Permission is granted to use this software on any computer system,
 *  and to redistribute it freely, subject to the following restrictions:
 * 
 *  1. The authors are not responsible for the consequences of use of
 *     this software, even if they arise from defects in the software.
 *  2. The origin of this software must not be misrepresented, either
 *     by explicit claim or by omission.
 *  3. Altered versions must be plainly marked as such, and must not
 *     be misrepresented as being the original software.
 *  4. This notice is to remain intact.
 *                                                                     
 *  Written by: Mark Austin                                       January, 1994
 *  ===========================================================================
 */

#include <stdio.h>   /* Standard Input/Output function declarations        */
#include <math.h>    /* Math functions, such as sqrt(x), and constant M_PI */
#include <stdlib.h> 

int main( void ) {
float fRadius; /* Radius of circle  */
float   fArea; /* Area of circle    */
float     fPi; /* Variable for "pi" */

   /* [a] : Prompt User for "radius of circle" */

   printf("============================================\n");
   printf("Please input the circle radius (Radius > 0):");
   scanf("%f", &fRadius);

   /* [b] : Check that the radius in greater than zero */

   if( fRadius <= 0 ) {
       printf("ERROR >> Circle radius must be greater than zero\n");
       exit (1);
   }

   /* [c] : Compute Area of Circle */

   fPi   = 4.0*atan( 1.0 );
   fArea = fPi*fRadius*fRadius;

   /* [d] : Print Radius and Area */

   printf("Radius of Circle = %8.3f \n", fRadius );
   printf("Area of Circle   = %8.3f \n", fArea );

   return (0);
}