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

float exp_diff_for(float x, float h)
{
    return (exp(x+h) - exp(x))/h ;
}

double exp_diff_back(double x, double h)
{
    return (exp(x-h) - exp(x))/h ;
}

double exp_diff_central(double x, double h)
{
    return (exp(x+h) - exp(x-h))/(2.0 * h);
}

int main()
{
  int n;
  float x = 1.0 , h, fx, err, ex;
  
  ex = exp(x);
  
  printf("# exact = %f\n", ex);
  printf("#   h         diff            error\n");
  for(h = 1e-1; h > 1e-6; h = h / 2.0)
  {
      fx = exp_diff_for(x, h);
      err = fabs((ex - fx) / ex);
      printf("%10.7lf %15.10lf %15.10lf\n", h, fx, err);
  }

  return 0;
}