for(conditions)
int x, y, timetaken;
x = (get the time for right now);
...more condions...
y = (get the time for right now);
timetaken= y-x;
...rest of code...

#include <stdio.h>
#include <time.h>
 
int main ()
{
  time_t start, endtime;
  unsigned long choice;
  unsigned long t;
  int difference;
  start = time(NULL);
  printf ("%ld seconds have passed since January 1, "
          "1970(Otherwise known as the Epoch)\n\nPlease enter the "
          "number to loop to: ", start);
  scanf("%ld", &choice);
  for(t = 0; t<choice; t++)     
        endtime=time(NULL);
  difference = difftime(endtime, start);
  printf("\n\nThe count to %ld took %d seconds!",t, 
          difference);
 
  return 0;
}