C++如何停止键盘循环输入

Question

键盘输入head1之后，通过按Ctrl+z停止输入，但也无法进入head2的cin输入了。
程序需要如果改？谢谢。

#include <iostream>
#include <cstdio>
using namespace std;
template <class T>
class Node
{
public:
    Node *prev, *next;
    T value;
    Node():prev(this),next(this){}
    Node(T x):prev(NULL),next(NULL),value(x){}
    Node(T x, Node *p, Node *n):prev(p),next(n),value(x){}
};
template <class T>
int calcLength(Node<T>* head)
{
    int nLen=0;
    Node<T> *p=head->next;
    while(p!=head)
    {
        nLen++;
        p=p->next;
    }
    return nLen;
}
int main()
{
    int tmp;
    cout << "input link1:" << endl;
    Node<int> *head1 = new Node<int>();
    Node<int> *p=head1;
    while (cin >> tmp)
    {
        if(tmp==NULL)break;
        Node<int> *p = new Node<int>(tmp, head1, head1->next);
        head1->next = head1->next->prev = p;
    }
    int len1=calcLength(p);

    cout << "input link2:" << endl;
    Node<int> *head2 = new Node<int>();
    p=head2;
    while (cin >> tmp)
    {
        if(tmp==NULL)break;
        Node<int> *p = new Node<int>(tmp, head2, head2->next);
        head2->next = head2->next->prev = p;
    }
    int len2=calcLength(p);

    cout << len1 << endl;
    cout << len2 << endl;
    return 0;
}

Answer 1

1.用ctrl+d试试;
2.或者修改代码
......
cin>>tmp;
while(tmp!=-1){
.......
cin>>tmp;
}
.......