950511-1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

main ()
{
  unsigned long long xx;
  unsigned long long *x = (unsigned long long *) &xx;

  *x = -3;
  *x = *x * *x;
  if (*x != 9)
    abort ();
  exit (0);
}