学步园

     双向链表的建立插入删除的方式与单链表类似，要注意的是双向链表的头部和尾部各有一个NULL指针，指示链表的结束。每个链表节点有两个指针分别是前驱指针和后继指针，指向前后两个节点。下面是双向链表的代码：

# include <stdio.h>
# include <stdlib.h>
struct list{
int num;
list *next,*prior;
};
typedef list *link;
int main()
{   link head=NULL;
    void print(link);
	link deletelist(link,int);
	link createlist(link);
	head=createlist(head);
	print(head);
	head=deletelist(head,1);
	print(head);
system("pause");
return 0;
}

link createlist(link head)
{
int item;
link p1,p2;
head=(link)malloc(sizeof(list));
printf("input the first element\n");
scanf("%d",&head->num);
head->next=NULL;
head->prior=NULL;
p1=head;
printf("input an element\n");
scanf("%d",&item);

while(item!=-1)
{
	p2=(link)malloc(sizeof(list));
	p2->num=item;
	p2->prior=NULL;
	p2->next=p1;
	p1->prior=p2;
	p1=p2;
	printf("input an element\n");
	scanf("%d",&item);
}
return head;
}

void print(link head)
{
link p=head;
for(;p!=NULL;p=p->prior)
	printf("%d\t",p->num);
printf("\n");
}

link deletelist(link head,int x)
{
	link p1=head;
	for(;p1->num!=x;p1=p1->prior)
	{}
	if(p1==head)
	{
		p1->prior->next=NULL;
		head=p1->prior;
		free(p1);
	}
	else if(p1->prior==NULL)
	{
		p1->next->prior=NULL;
	free(p1);
	}
	else{
	p1->prior->next=p1->next;
	p1->next->prior=p1->prior;
	free(p1);
	}
	return head;

}