双向链表的实现

　　由于一直对链表不太熟，所以今天晚上就趁着没什么事，写个双向链表玩玩。

#include<iostream>
using namespace std;
struct Node
{
    int Num=0;
    Node *Next=nullptr;
    Node *Pre=nullptr;
};

int main()
{
    Node *head, *current, *pre=nullptr;
    int count = 2;
    //为什么一开始就给head分配内存，而不是像单向链表那样由current将内存分配给head呢？
    //原因是如果一开始没有给head分配内存，那么在实现双向链表最关键的一步----head->next=current,current=head,这一步上就会出错
    //因为一开始head是没有分配内存给他的，所以将current的内存给了head，而current本身只能和head共享一块内存了，这样就不能实现双向性了

    head = new Node;
    head->Num = count - 1;
    while (count <= 10)
    {
        current = new Node;
        if (head->Next == nullptr)
        {
            head->Next = current;
            current->Pre = head;
            current->Num = count;
        }
        else
        {
            pre->Next = current;
            current->Pre = pre;
            current->Num = count;
        }
        pre = current;
        current = current->Next;
        ++count;
    }
    //正序输出
    current = head;
    while (current->Next != nullptr)
    {
        cout << current->Num << " ";
        current = current->Next;
    }
    cout << current->Num;
    cout << endl;
    //逆序输出
    current = current;
    while (current != nullptr)
    {
        cout << current->Num << " ";
        current = current->Pre;
    }





    system("pause");
    return 0;
}