Testpanel = ptr_first (PanelB);
while (Testpanel)
{
do_something_with(Testpanel);
Testpanel = Testpanel->link.next;
}

All objects struct are defined in atypes.h, there you can look up their members, like the C_LINK. BTW, don't set flags to 0 - reset the VISIBLE flag instead. Setting flags to 0 might also delete important internal flags.