#include <math.h>
main()  /* Program 5: Approximate a Derivative by a 
                      Difference Quotient*/
{
   int n = 1;
   double x = 1.0, h = 1.0, deriv = cos(x), diffquo, error;

   printf(" deriv =%13.6e \n", deriv);
   printf("   h      diffquo  abs(deriv - diffquo) \n");

   /* Let h range from 10^{-1} down to 10^{-20} */

   while(n <= 20) {
      h = h/10;                       /* h = 10^(-n) */
      diffquo = (sin(x+h)-sin(x))/h;  /* difference quotient */
      error = fabs(deriv - diffquo);  
      printf("%5.1e %13.6e %13.6e \n", h, diffquo, error);
      n++;
   }
}