void swap(Node* node1, Node* node2, List* l)
{
         Node* temp_node1;
         Node* temp_node2;
         Node* temp;

         temp_node1 = node1;
         temp_node2 = node2;
         if ( temp_node1 == l->first){l->first = temp_node2;}
         else if ( temp_node2 == l->first){l->first = temp_node1;}
         if ( temp_node1 == l->last){l->last = temp_node2;}
         else if ( temp_node2 == l->last){l->last = temp_node1;}

         if (temp_node1->next!=NULL) { temp_node1->next->previous = temp_node2; }
         if (temp_node2->next!=NULL) { temp_node2->next->previous = temp_node1; }
         temp = temp_node1->next;
         temp_node1->next = temp_node2->next;
         temp_node2->next = temp;

         if (temp_node1->previous!=NULL) { temp_node1->previous->next = temp_node2;  }
         if (temp_node2->previous!=NULL) { temp_node2->previous->next = temp_node1;  }
         temp = temp_node1->previous;
         temp_node1->previous = temp_node2->previous;
         temp_node2->previous = temp;

         node1 = temp_node2;
         node2 = temp_node1;
}


//------------------------------------------------------------------------------

void sort(List* l)
{
    Node* current;
    Node* item;
    Node* min;
    if ( l->first != NULL)
    {
        for(item = l->first; item != NULL; item = item->next)
        {
            min = item;
            for(current = item->next; current != NULL; current = current->next)
            {
                if (current->element < min->element)
                {
                    min = current;
                }

            }
            if ( min != item)
            {
                swap(item, min, l);
                item = l->first;
            }
        }
    }
    else
    {
        cout<<"Een lege lijst kan niet gesorteerd worden"<<endl;
    }
}