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。

1 #include
     
       2 using namespace std; 3 struct Node 4 { 5     int Num=0; 6     Node *Next=nullptr; 7     Node *Pre=nullptr; 8 }; 9 10 int main()11 {12     Node *head, *current, *pre=nullptr;13     int count = 2;14     //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？15     //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16     //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17 18     head = new Node;19     head->Num = count - 1;20     while (count <= 10)21     {22         current = new Node;23         if (head->Next == nullptr)24         {25             head->Next = current;26             current->Pre = head;27             current->Num = count;28         }29         else30         {31             pre->Next = current;32             current->Pre = pre;33             current->Num = count;34         }35         pre = current;36         current = current->Next;37         ++count;38     }39     //正序输出40     current = head;41     while (current->Next != nullptr)42     {43         cout << current->Num << " ";44         current = current->Next;45     }46     cout << current->Num;47     cout << endl;48     //逆序输出49     current = current;50     while (current != nullptr)51     {52         cout << current->Num << " ";53         current = current->Pre;54     }55 56 57 58 59 60     system("pause");61     return 0;62 }