#include <fstream.h>
#include "clist.h"
#include "clistf.h"
#include "poly.h"

void main (void)
{
     Poly      equation[5];        // Array of equations
     Poly      derivative[5];      // Array of derivatives
     Poly      sum;                // Sum of equations
     Poly      dsum;               // Derivative of sum
     double    point[3];           // Three data points
     double    slope;              // Slope of tangent at point
     double    value;              // Value of sum equation
     int       j, k;               // Loop counters
     fstream   fi;                 // Input stream
     fstream   fo;                 // Output stream

     fi.open ("a:\\poly.dat", ios::in);
    if (fi.fail())
     {
          cout << "Problem opening data file\n";
          return;
     }
     fo.open ("a:\\poly.ans", ios::out);
     if (fo.fail())
     {
          cout << "Problem opening result file\n";
          return;
     }
     for (k = 0; k < 3; k++)
          fi >> point[k];
     for (j = 0; j < 5; j++)
     {
          equation[j].Get(fi);                  // Read an equation
          derivative[j] = equation[j].Dx();    // Create the derivative
          sum = sum + equation[j];             // Add equation to sum
          fo << "\nFor ";
          equation[j].Put(fo);               // Output equation
          for (k = 0; k < 3; k++)
          {                                    // Evaluate at a point
               slope = derivative[j].Eval(point[k]); 
               fo << "The slope at " << point[k]
                    << " is " << slope << "\n";
          }
     }
     fi.close();
     dsum = sum.Dx();                             // Take derivative of sum
     fo << "\nSum polynomial:\n";
          sum.Put(fo);
     fo << "Derivative:\n";
     dsum.Put(fo);
     fo << endl;
        for (k = 0; k < 3; k++)
        {    value = sum.Eval(point[k]);          // Compute value at point
             fo << "At " << point[k] << " the value is "   // Compute slope
                << value << "; the slope is " << dsum.Eval(point[k]) << endl;
        }

//          The following statements should be uncommented if you do 
//          the extra credit
//   fo << "The net area between " << point[0] << " and " << point[2];
//   fo << " is " << sum.Integrate(point[0], point[2]) << endl;
    fo.close();
}