lightoj - 1022 - Circle in Square

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
double pi= 2* acos(0.0);
int main()
{
   int t,c;
   cin>>t;
   for(c=1;c<=t;c++)
   {
       double r,l;
       cin>>r;
       l=r*2;
       double x=l*l-pi*r*r;
       cout<< "Case "<<c<<setprecision(2)<<fixed<< ": "<<x<<endl;
   }
}