// Compute total weight of a batch of washers
#include <stdio.h>
#include <math.h>
#define PI 3.14159

double circle_area(double);

int main(void) {
	double d1,             // hole circle's diameter
	       d2,             // big circle's diameter
	       thickness,      
	       density;        
	int    qty;            

	double unit_weight,    // single washer's weight
	       total_weight,   // a batch of washers' total weight
	       rim_area;       // single washer's rim area 

	printf("Inner diameter in cm: ");
	scanf("%lf", &d1);
	printf("Outer diameter in cm: ");
	scanf("%lf", &d2);
	printf("Thickness in cm: ");
	scanf("%lf", &thickness);
	printf("Density in grams per cubic cm: ");
	scanf("%lf", &density);
	printf("Quantity: ");
	scanf("%d", &qty);

	// compute weight of a single washer
	rim_area = circle_area(d2) - circle_area(d1);
	unit_weight = rim_area * thickness * density;

	// compute weight of a batch of washers
	total_weight = unit_weight * qty;

	printf("Total weight of %d washers is %.2f grams.\n", 
	       qty, total_weight);

	return 0;
}

double circle_area(double diameter) {
	return pow(diameter/2, 2) * PI;
}