List node

#include<iostream>using namespace std;struct node{int data;node *next;};class List{public:List();List(List &L);~List();void insert(const int);bool IsEmpty();size_t ListLen();int GetElem(size_t);void append(size_t,int);//在第i个位置插入数值void Display();void remove(size_t);int FindElem(int elm);void merge(List &L);    node* GetFN();node* GetEN();private:node *p;};List::List(){p = new node;p->next = NULL;}//这里还是有问题的List::List(List &L){p = L.GetFN();}List::~List(){delete p;}node* List::GetFN(){return p;}node* List::GetEN(){node *q = p->next, *pre = q;while (q){pre = q;q = q->next;}    return pre;}void List::insert(const int a){node *q = p;while (q->next){q = q->next;}node *m = new node;m->data = a;m->next = NULL;q->next = m;}void List::Display(){node *q = p->next;while(q){cout << q->data << " ";q = q->next;}cout << endl;}bool List::IsEmpty(){   node *q = p->next;   return q==NULL?1:0;}size_t List::ListLen(){if(IsEmpty())return 0;node *q = p->next;size_t i = 0;while (q){++i;q = q->next;}return i;}int List::GetElem(size_t i){node *q = p->next, *pre = q;while (i--){if(!q)  throw runtime_error("error"); pre = q;       q = q->next;}return (*pre).data;}void List::append(size_t i,int a){node *q = p->next, *pre = q;while (i--){if(!q)throw runtime_error("error"); pre = q;q = q->next;}node *m = new node;m->data = a;m->next = q;pre->next = m;}void List::remove(size_t i){node *q = p->next, *pre = q;while (--i){if(!q)throw runtime_error("error"); pre = q;q = q->next;}    pre->next = q->next;delete q;}void List::merge(List &L){   this->GetEN()->next = L.GetFN()->next;}int List::FindElem(int elm){node *q = p->next, *pre = q;int i = 0;while (q){++i;    if((*q).data == elm)return i;pre = q;q = q->next;}    if(q == NULL)throw runtime_error("can't find");  }int main(){List l,m;l.insert(1);l.insert(12);l.insert(10);l.Display();m.insert(0);m.insert(-90);m.Display();l.merge(m);l.Display();    cout << endl;//cout << l.GetElem(3);}