gistfile1.c

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

#define PHI ((1 + sqrt (5)) / 2)

/**
 * Get an integer above a given minimum value.
 *
 * @param The prompt to display
 * @param The minimum value
 *
 * @return Integer in the range [min, INT_MAX]
 */
int
getint (char* prompt, int min)
{
  int out;

  do
    {
      printf (prompt);
      scanf  ("%i", &out);
    }
  while (out <= min);

  return out;
}

int
main (void)
{
  int result = 1, lastresult = 0, resultbeforelast = 0, increment, limit;
  double phi, error;

  limit = getint ("Enter upper bound greater than zero: ", 0);

  do
    {
      printf ("%i \n", result);
      
      resultbeforelast = lastresult;
      lastresult       = result;
      result           = result + increment;
      increment        = lastresult;
      
      phi   = (double)lastresult / (double)resultbeforelast;
      error = fabs ((100 * (PHI - phi)) / PHI);
    }
  while (result <= limit);
  
  printf ("Approximation of phi = %i / %i = %f \n", lastresult, resultbeforelast, phi);
  printf ("True value of phi    = %f\n", PHI);
  printf ("Percentage error     = %f%%\n", error);

 return 0;
}