/* File: washer3.c

   This program computes the area of a flat washer.

   This time we give main() a return type.
   There should be no warnings now, when compiled with -Wall.
*/

#include <stdio.h>
#include <math.h>

#define PI 3.1415927


// This is a function prototype
double circleArea(double) ;


int main() {
   double outerDiameter, innerDiameter ;
   double outerArea, innerArea ;
   double washerArea ;

   printf("Outer Diameter = ") ;
   scanf("%lf", &outerDiameter) ;

   printf("Inner Diameter = ") ;
   scanf("%lf", &innerDiameter) ;

   // Compute some values using x & y

   outerArea = circleArea(outerDiameter) ;
   innerArea = circleArea(innerDiameter) ;
   washerArea = outerArea - innerArea ;

   printf("The area of a washer with outer diameter = %f ", 
      outerDiameter) ;
   printf("and inner diameter = %f ", innerDiameter) ;
   printf("is %f \n", washerArea) ;

   return 0 ;
}


/* Calculate the area of a circle. */
double circleArea (double diameter) {
   double area, radius ; 

   radius = diameter / 2.0 ;
   area = PI * radius * radius ;

   // printf("diameter = %f, radius = %f and area = %f\n", 
   //   diameter, radius, area) ;

   return area ;
}