struct snake* New_Head
New_Head = (struct snake*)malloc(sizeof(struct snake))
/* 新的头结点的位置自己写吧。*/
New_Head ->next = head/*head 是这个链表的头指针,自己改。*/
head ->previous = New_Head/*这是双向链表所要的。*/
tail ->previous ->next = NULL
tail ->previous = NULL
free(tail)