/* From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
   by RH Landau, MJ Paez, and CC Bordeianu 
   Copyright Wiley-VCH, 2007.
   Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
   MJ Paez, Univ Antioquia, 2007; & CC Bordeianu, Univ Bucharest, 2007
   Support by National Science Foundation
*/
// area.c: Area of a circle, sample I/O  

#include <stdio.h> 
#define PI 3.1415926535897932385E0
main() { 
	
   double radius, area;                          // declare variables
	 
   printf("Enter the radius of a circle \n");       // ask for radius
   scanf("%lf", &radius);                           // read in radius
   area = radius * radius * PI;                       // area formula
   printf("radius=%f, area=%f\n", radius, area);     // print results
}