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

#define ERROR_BOUND 1e-10

double f[10];
int d;

void readpoly ( int d )
{
   int i;

   for (i=0; i<=d; ++i) {
      f[i] = (double)(rand() % 11 - 5);
      if (i == d) while (f[i] == 0) f[i] = (double)(rand() % 11 - 5);
      printf("Coefficient of x^%d = %lf\n", i, f[i]);
   }
   printf("The input polynomial is:\n\tf(x) = ");
   for (i=d; i>=0; --i) printf("(%d)*x^%d%c", (int)f[i], i, (i)?'+':'\n');
}

double evalpoly ( double x )
{
   double sum = 0, xpower = 1;
   int i;

   for (i=0; i<=d; ++i) {
      sum += f[i] * xpower;
      xpower *= x;
   }
   return sum;
}

double findroot ( double a, double b )
{
   double m, fm, fa, fb;

   fa = evalpoly(a); fb = evalpoly(b);
   while (fa * fb < 0) {
      m = (a + b) / 2;
      fm = evalpoly(m);
      if (fabs(fm) < ERROR_BOUND) return m;
      if (fa * fm < 0) {
         b = m; fb = fm;
      } else {
         a = m; fa = fm;
      }
   }
   printf("??? Invalid input detected in findroot()\n");
   exit(2);
}

int main ()
{
   double fa, fb, root;
   int i;

   srand((unsigned int)time(NULL));
   printf("Enter degree (2 <= d <= 9): "); scanf("%d", &d);
   if ((d < 2) || (d > 9)) d = 5;
   readpoly(d);
   fa = 0;
   for (i=0; i<=10; ++i) {
      fb = evalpoly((double)i);
      if (abs(fb) < ERROR_BOUND) {
         printf("+++ Integer root located: %d\n", i);
         exit(0);
      }
      if (fa * fb < 0) {
         root = findroot(i-1,i);
         printf("+++ Real root located: %14.12lf\n", root);
         exit(0);
      }
      fa = fb;
   }
   printf("!!! Failure to detect a root\n");
   exit(1);
}