Circle in Square Lightoj 1022

 The equation used in this problem is:

Shaded area= area of the Square - Area of the circle

#include<iomanip>
#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    int t,i;
    cin>>t;
    for(i=1;i<=t;i++){
        double r,pi,ca,sa,ra;
        cin>>r;
        pi=2*acos(0.0);
       ca=pi*(r*r);
       sa=(2*r)*(2*r);
       ra=sa-ca;
        cout<<"Case "<<i<<": "<<fixed<<setprecision(2)<<ra<<endl;
}
    return 0;
}