// time.c
//
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include <stdio.h>
#include <math.h>

main()
{
  time_t  t0, t1; /* time_t is defined on <time.h> and <sys/types.h> as long */
  clock_t c0, c1; /* clock_t is defined on <time.h> and <sys/types.h> as int */

  long count;
  double a, b, c;

  printf ("using UNIX function time to measure wallclock time ... \n");
  printf ("using UNIX function clock to measure CPU time ... \n");

  t0 = time(NULL);
  c0 = clock();

  printf ("\tbegin (wall):            %ld\n", (long) t0);
  printf ("\tbegin (CPU):             %d\n", (int) c0);

  printf ("\t\tsleep for 5 seconds ... \n");
  sleep(5);

  printf ("\t\tperform some computation ... \n");
  for (count = 1l; count < 10000000l; count++) {
     a = sqrt(count);
     b = 1.0/a;
     c = b - a;
  }

  t1 = time(NULL);
  c1 = clock();

  printf ("\tend (wall):              %ld\n", (long) t1);
  printf ("\tend (CPU);               %d\n", (int) c1);
  printf ("\telapsed wall clock time: %ld\n", (long) (t1 - t0));
  printf ("\telapsed CPU time:        %f\n", (float) (c1 - c0)/CLOCKS_PER_SEC);
}