/* bad_roundoff.c  remember 0.1 can not be exactly stored in binary */
/*                 each additional use makes it worse!              */

#include <stdio.h>

double h=0.1;   /* approximate     */
int n3=3;       /* there are exact */
int n80000=80000;
int n10000=10000;

int main(int argc, char *argv[])
{
  double h4 = h;
  double h0001 = 0.0001;
  double abad = 0.0;
  double agood = 0.0;
  int i;

  printf("bad_roundoff.c running \n\n");

  for(i=0; i<n3; i++) h4 = h4*h;
  printf("h4 should be 0.0001, is %20.17f, 10000*h4= %20.17f \n",
	 h4, 10000*h4);
  printf("                         h0001 * 10000  should be 1,  = %20.17f \n\n",
         h0001*10000);

  for(i=0; i<n80000; i++) abad = abad+h4;  /* could use each */
  printf("abad  should be 8, is %20.17f \n", abad);

  for(i=0; i<n80000; i++) agood = (i+1)*h0001;  /* could use each */
  printf("agood should be 8, is %20.17f \n\n", agood);

  printf("abad*abad+abad*abad    128, is %22.17f \n", abad*abad+abad*abad);
  printf("agood*agood+agood*agood     is %22.17f \n\n", agood*agood+agood*agood);
  return 0;
} /* end bad_roundoff.c */