Pr11-2

 // This program stores data about a circle in a structure.

#include <iostream>
#include <cmath>  // For the pow function
#include <iomanip>
using namespace std;

// Constant for Pi.
const double PI = 3.14159;

// Structure declaration
struct Circle
{
   double radius;      // A circle's radius
   double diameter;    // A circle's diameter
   double area;        // A circle's area
};

int main()
{
   Circle c;    // Define a structure variable

   // Get the circle's diameter.
   cout << "Enter the diameter of a circle: ";
   cin >> c.diameter;

   // Calculate the circle's radius.
   c.radius = c.diameter / 2;

   // Calculate the circle's area.
   c.area = PI * pow(c.radius, 2.0);

   // Display the circle data.
   cout << fixed << showpoint << setprecision(2);
   cout << "The radius and area of the circle are:\n";
   cout << "Radius: " << c.radius << endl;
   cout << "Area: " << c.area << endl;
   return 0;
}