谁帮我看看这是哪里有问题啊，结果很多没有输出了

img

img

img

img

int main()
{
List L;
cout<<"enter 10 integers:\n";
int item;
for(int i=0;i<10;i++)
{
cin>>item;
L.Push_back(item);
}
List::iterator itr=L.Begin();
cout<<"after operator++():"<<endl;
cout<<(++itr)<<endl;
cout<<"after operator--():"<<endl;
cout<<(--itr)<<endl;
L.Erase(itr); //删除第一个元素
cout<<"after erasing the first:"<<endl;
display_list(L.Begin(),L.End());

L.Pop_back();                //尾删
cout<<"after erasing the last:"<<endl;
display_list(L.Begin(),L.End());

cout<<"the first and the last:"<<endl;
cout<<L.Front()<<endl;    //输出首元素
cout<<L.Back()<<endl;    //输出尾元素

//新增的语句
cout<<"update the first and the last:"<<endl;
L.Front()=100;
L.Back()=200;
display_list(L.Begin(),L.End());
return 0;
}

img