一、双向循环列表
head.h
#ifndef __head_h__
#define __head_h__
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
enum
{
SUCCESS,
FALSE=-1
};
typedef char datatype;
//双向列表结构体
typedef struct Node
{
//存数据域
datatype data;
//存上一个地址
struct Node *back;
//存下一个地址
struct Node *next;
}*Doublelink;
//头插
Doublelink insert_head(datatype element,Doublelink head);
//输出
void output_head(Doublelink head);
//头删
Doublelink delete_head_link(Doublelink head);
//尾插
Doublelink insert_back_link(Doublelink head,datatype element);
//尾删
Doublelink delete_back_link(Doublelink head);
#endif main.c
#include "head.h"
int main(int argc, const char *argv[])
{
Doublelink head=NULL;//定义双向列表头节点
int n;
printf("请输入n的值：");
scanf("%d",&n);
datatype element;
for(int i=0;i<n;i++)
{
printf("请输入%d个数的值：",i+1);
getchar();
element=getchar();
head=insert_head(element,head);
}
//输出
output_head(head);
//头删
printf("头删后的结果为：\n");
head=delete_head_link(head);
output_head(head);
//尾插
printf("请输入在末尾要插入的值：");
getchar();
element=getchar();
printf("尾插后的结果为：\n");
head=insert_back_link(head,element);
output_head(head);
//尾删
printf("尾删后的结果为：\n");
head=delete_back_link(head);
output_head(head);
return 0;
} test.c
#include "head.h"
//创建节点
Doublelink create_node()
{
Doublelink s=(Doublelink)malloc(sizeof(struct Node));
if(NULL==s)
return NULL;
//新节点的数据域初始化
s->data=0;
//指针域初始化
s->next=s->back=s;
return s;
}
//头插
Doublelink insert_head(datatype element,Doublelink head)
{
//创建新节点
Doublelink s=create_node();
s->data=element;
//链表为空
if(head==NULL)
head=s;
//存在至少一个节点
else
{
Doublelink rear=head->back;
s->next=head;
head->back=s;
head=s;
rear->next=head;
head->back=rear;
}
return head;
}
//遍历(正向)
void output_head(Doublelink head)
{
//链表为空
if(head==NULL)
{
printf("输出失败\n");
return;
}
else
{
Doublelink p=head;
do
{
printf("%c ",p->data);
p=p->next;
}while(p!=head);
putchar(10);
}
}
//头删
Doublelink delete_head_link(Doublelink head)
{
//链表为空
if(head==NULL)
{
printf("删除失败\n");
return head;
}
else
{
Doublelink p=head;
head=head->next;
head->back=p->back;
p->back->next=head;
free(p);
p=NULL;
return head;
}
}
//尾插
Doublelink insert_back_link(Doublelink head,datatype element)
{
Doublelink s=create_node();
s->data=element;
if(head==NULL)
head=s;
Doublelink p=head;
while(p->next!=head)
{
p=p->next;
}
p->next=s;
s->next=head;
s->back=p;
head->back=s;
return head;
}
//尾删
Doublelink delete_back_link(Doublelink head)
{
//判断为空
if(head==NULL)
{
printf("尾删失败\n");
return head;
}
Doublelink p=head->back;
Doublelink q=p->back;
q->next=head;
head->back=q;
free(p);
p=NULL;
return head;
} 
二、双向链表的尾删
//尾删
void delete_back_link(Doublelink head)
{
//判断为空
if(head==NULL)
{
printf("尾删失败\n");
return ;
}
Doublelink p=head;
if(p->next==NULL)
{
head=delete_head_link(head);
return;
}
while(p->next!=NULL)
{
p=p->next;
}
p->back->next=NULL;
free(p);
p=NULL;
return ;
} 