#include 
    
     enum {kIsSmaller,kIsLarger, kIsSame};class Data{    public:        Data(int newVal):value(newVal){}        ~Data(){}        int compare(const Data&);        void show(){std::cout << value << "\n";}    private:        int value;};int Data::compare(const Data& otherData){    if(value < otherData.value)        return kIsSmaller;    if(value > otherData.value)        return kIsLarger;    else        return kIsSame;}class Node;class HeadNode;class TailNode;class InternalNode;class Node{    public:        Node() {}        virtual ~Node(){}        virtual Node* insert(Data*data) =0;        virtual void show() = 0;    private:};class InternalNode: public Node{    public:        InternalNode(Data*dara, Node*next);        virtual ~InternalNode() {delete next;delete data;}        virtual Node *insert(Data*data);        virtual void show(){            data -> show();            data -> show();        }    private:        Data *data;        Node *next;};InternalNode::InternalNode(Data* newData, Node *newNext):    data(newData), next(newNext){    }Node *InternalNode::insert(Data *otherData){    int result = data->compare(*otherData);    switch(result){        case kIsSame:        case kIsLarger:{                           InternalNode *dataNode = new InternalNode(otherData, this);                           return dataNode;                       }        case kIsSmaller:                       next = next->insert(otherData);                       return this;    }}class TailNode:public Node{    public:        TailNode(){}        virtual ~TailNode(){}        virtual Node *insert(Data *data);        virtual void show(){}    private:};Node * TailNode::insert(Data *data){    InternalNode *dataNode = new InternalNode(data,this);    return dataNode;}class HeadNode:public Node{    public:        HeadNode();        virtual ~HeadNode() {delete next;}        virtual Node * insert(Data *data);        virtual void show(){next ->show();}    private:        Node *next;};HeadNode::HeadNode(){    next = new TailNode;}Node * HeadNode::insert(Data*data){    next = next -> insert(data);    return this;}class LinkedList{    public:        LinkedList();        ~LinkedList(){delete head;}        void insert(Data*data);        void showAll() {head -> show();}    private:        HeadNode * head;};LinkedList::LinkedList(){    head = new HeadNode;}void LinkedList::insert(Data* pData){    head -> insert(pData);}int main(){    Data * pData;    int val;    LinkedList ll;    while(true){        std::cout << "What value (0 to stop)?";        std::cin >> val;        if (!val)            break;        pData = new Data(val);        ll.insert(pData);    }    ll.showAll();    return 0;}