NCTU LAB 02/04 NUM 3

#include <iostream>
#include <iomanip>
using namespace std;

#define PI 3.1415926
#define pTwo(x) x*x

struct Circle{
    double radius;
};

struct Ring{
    Circle c1, c2;
}ring;

double area(Ring ring){
    return PI*pTwo(ring.c2.radius) - PI*pTwo(ring.c1.radius);
}

int main(){
    double startX, startY, smallRadius, largeRadius;
    while(cin >> startX >> startY >> largeRadius >> smallRadius){
        ring.c1.radius = smallRadius;
        ring.c2.radius = largeRadius;
        cout << fixed << setprecision(6) << "Area: " << area(ring) << endl;
    }
    return 0;
}