// This program calculates the area of a circle.
// The formula for the area of a circle is Pi times
// the radius squared. Pi is 3.14159.
#include <iostream>
#include <cmath>   // needed for pow function
using namespace std;

int main()
{
   const double PI = 3.14159;
   double area, radius;

   cout << "This program calculates the area of a circle.\n";
   cout << "What is the radius of the circle? ";
   cin >> radius;
   area = PI * pow(radius, 2.0);
   cout << "The area is " << area << endl;
   return 0;
}