Removal of tail recursion in C++

static void new_tristrip(polygon_node **tn, edge_node *edge,
                         double x, double y)
{ polygon_node *temptn,*Stemp;

  #if 0
/* this part is the code i want to work */
    MALLOC(temptn, sizeof(polygon_node), "tristrip node creation", polygon_node);
    (temptn)->next= NULL;
    (temptn)->v[LEFT]= NULL;
    (temptn)->v[RIGHT]= NULL;
    (temptn)->active= 1;
    add_vertex(&(temptn->v[LEFT]), x, y);
    edge->outp[ABOVE]= temptn;
   if(!(*tn))
      tn=&temptn;
   else
     { Stemp=(*tn)->next;
       while((Stemp->next))Stemp=Stemp->next;
        Stemp->next=temptn;
     }
    return;

  #else
/* this is the tail recursive code */
  if (!(*tn))
  {
    MALLOC(*tn, sizeof(polygon_node), "tristrip node creation", polygon_node);
    (*tn)->next= NULL;
    (*tn)->v[LEFT]= NULL;
    (*tn)->v[RIGHT]= NULL;
    (*tn)->active= 1;
    add_vertex(&((*tn)->v[LEFT]), x, y);
    edge->outp[ABOVE]= *tn;
  }
  else
    /* Head further down the list */
    new_tristrip(&((*tn)->next), edge, x, y);
  #endif
}