C++ if-else Statement to check double type value

#include <iostream>
#include <cmath>
using namespace std;
int main()//from w  w w.  ja  v a2  s .  c om
{
   double radius;
   cout << "Please type in the radius: ";
   cin  >> radius;
   if (radius < 0.0)
      cout << "A negative radius is invalid" << endl;
   else
      cout << "The area of this circle is " << 3.1416 * pow(radius,2) << endl;
      return 0;
}