C/time.h/difftime

    
//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.
*/