961213-1.c

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

int
g (unsigned long long int *v, int n, unsigned int a[], int b)
{
  int cnt;
  *v = 0;
  for (cnt = 0; cnt < n; ++cnt)
    *v = *v * b + a[cnt];
  return n;
}

main ()
{
  int res;
  unsigned int ar[] = { 10, 11, 12, 13, 14 };
  unsigned long long int v;

  res = g (&v, sizeof(ar)/sizeof(ar[0]), ar, 16);
  if (v != 0xabcdeUL)
    abort ();

  exit (0);
}