双向链表循环

双向列表尾插

//尾删
doublelink del_last(doublelink head)
{
	if(head==NULL)
	{
		printf("数据为空，无法尾删");
		return head;
	}
	else if(head->next==NULL)
	{
		head=del_head(head);//头删即尾删
	}
	else
	{
		doublelink s=head;
		while(s->next!=NULL)
		{
			s=s->next;
		}
		doublelink del=s;
		s->prev->next=NULL;
		free(del);
		del=NULL;
		return head;

	}

}

head.h

#ifndef __HEAD_H__
#define __HEAD_H__
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct node
{
	char data;
	struct node *next;
	struct node *prev;
}*doublelink;
typedef char datatype;
doublelink create();
doublelink del_head(doublelink head);
doublelink putout(doublelink head);
doublelink del_last(doublelink head);
doublelink insert_last(doublelink head,datatype element);
doublelink insert_head(datatype element,doublelink head);
#endif

main.c

#include "head.h"
int main(int argc, const char *argv[])
{
	int n;
	doublelink head=NULL;
	printf("请输入创建的元素个数：");
	scanf("%d",&n);
	datatype element;
	for(int i=0;i<n;i++)
	{
		printf("请输入元素 %d element：",i+1);
		getchar();
		element=getchar();
//头插

		head=insert_head(element,head);
	}
	putout(head);
	
//头删
	head=del_head(head);
	putout(head);
//尾插

	printf("请输入尾插的元素element：");
	getchar();
	element=getchar();
	insert_last(head,element);
	putout(head);

//尾删
	
	printf("尾删后结果：\n");
	del_last(head);
	putout(head);
	
	
	return 0;
}

test.c

#include "head.h"
//创建空表
doublelink create()
{
	doublelink s=(doublelink)malloc(sizeof(struct node));	
	if(s==NULL)
	{
		return NULL;
	}
	s->data='\0';
	s->next=s;
	s->prev=s;
	return s;
}
//头插
doublelink insert_head(datatype element,doublelink head)
{
	doublelink s=create();
	s->data=element;
	//为空
	if(head==NULL)
	{
		head=s;
	}
	else
	{
		doublelink p=head;
		while(p->next!=head)
		{
			p=p->next;
		}
		s->next=head;
		head->prev=s;
		p->next=s;
		s->prev=p;
		head=s;
	}
	return head;

}
//遍历(逆向)
doublelink putout(doublelink head)
{
	doublelink p=head;
	if(head==NULL)
		printf("数据为空");
	else
	{
	do{
		printf("%c",p->data);
		putchar(32);
		p=p->next;
	}while(p!=head);
	}
	putchar(10);
	return head;

}
//头删除
doublelink del_head(doublelink head)
{
	if(head==NULL)
	{
		return NULL;	
	}
	else if(head->next==head)
	{
		free(head);
		head=NULL;
		return head;
	}
	else
	{
		doublelink rear=head;
		while(rear->next!=head)
		{
			rear=rear->next;
		}
		doublelink s=head;
		head=head->next;
		head->prev=rear;
		rear->next=head;
		free(s);
		s=NULL;
		return head;
	}
}
//尾插
doublelink insert_last(doublelink head,datatype element)
{
	if(head==0)
	{
		head=insert_head(element,head);	
	}
	else
	{
		doublelink rear=head;
		while(rear->next!=head)
		{
			rear=rear->next;
		}
		doublelink p=create();
		p->data=element;
		p->prev=rear;
		rear->next=p;
		p->next=head;
		head->prev=p;
		return head;

	}
}
//尾删
doublelink del_last(doublelink head)
{
	if(head==NULL)
	{
		printf("数据为空，无法尾删");
		return head;
	}
	else if(head->next==head)
	{
		head=del_head(head);//头删即尾删
	}
	else
	{
		doublelink del=head;
		while(del->next!=head)
		{
			del=del->next;
		}
		del->prev->next=head;
		head->prev=del->prev;
		free(del);
		del=NULL;
		return head;

	}

}