add: liste_tmp = liste_tmp -> next;
context: cached_exchange_rate ( struct struct_devise * currency1, 		       struct struct_devise * currency2 ){  GSList * liste_tmp = cached_exchange_rates;  struct cached_exchange_rate * tmp;  while ( liste_tmp )    {      tmp = liste_tmp -> data;      if ( currency1 == tmp -> currency1 && currency2 == tmp -> currency2 )	return tmp;    }  return NULL;}