#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

#define NPOINTS 20

int main ()
{
   int i;
   float X[NPOINTS], Y[NPOINTS], maxR, minR, r;

   srand((unsigned int)time(NULL));

   for (i=0; i<NPOINTS; ++i) {
      X[i] = (float)(rand() % 21 - 10);
      Y[i] = (float)(rand() % 21 - 10);
   }

   maxR = -15; minR = 15;
   for (i=0; i<NPOINTS; ++i) {
      printf("Point %2d : (%8.4f,%8.4f).  ", i, X[i], Y[i]);
      r = sqrt(X[i]*X[i]+Y[i]*Y[i]);
      printf("Distance from origin : %7.4f.\n", r);
      if (r > maxR) maxR = r;
      if (r < minR) minR = r;
   }
   printf("Radii of the smallest ring:\n");
   printf("Inner radius : %7.4f\n", minR);
   printf("Outer radius : %7.4f\n", maxR);
   printf("Area : %8.4f\n", 3.141593 * (maxR*maxR - minR*minR));
}