求救!一个关于线性表的插入操作,要求用C++;写一个完整的程序.请哪位大虾帮一下.

#include<iostream.h>
template <class elem>
class link
{
public:
elem element;
link *next;
link(const elem &elemval,link *nextval=NULL)
{
element=elemval;next=nextval;
}
link(link *nextval=NULL)
{
next=nextval;
}
};
template<class elem>
class llist:public link<elem>
{
private:
link<elem> *head;
link<elem> *tail;
link<elem> *fence;
int leftcnt,rightcnt;
void init()
{
fence=tail=head=new link<elem>;
leftcnt=rightcnt=0;
}
void removeall()
{
while(head!=NULL)
{
fence=head;
head=head->next;
delete fence;
}
}
public:
llist(int size=DefaultLstsizeSize)
{
init();
}
~llist()
{
removeall();
}
bool insert(elem);
bool