C/time.h/difftime

difftime: returns the difference, in seconds, between time1 and time2( time2 - time1)

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//Declaration: double difftime(time_t time2, time_t time1);

 #include <time.h>
 #include <stdio.h>
 int main(void)
 {
   time_t start, end;
   volatile long unsigned t;
   start = time(NULL);
   for(t=0; t<500; t++) ;
   end = time(NULL);
   printf("Loop used %f seconds.\n", difftime(end, start));
   return 0;
 }
        

/* Loop used 0.000000 seconds.

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