与单链表相比只是修改略微的代码就可实现

为啥返回为h?

#include<stdio.h>
#include<malloc.h>
#define ListSize 100
struct Data{
	int bookID;
	char bookName[20];
	double bookPrice;
};
typedef Data DataType;
typedef struct BookList{
	DataType data;
	struct BookList *next;
};
//单链表初始化 
BookList * InitList(BookList *h){
	h=(BookList *)malloc(sizeof(BookList));//创建头结点 
	if(h==NULL){
		return 0;
	}
	h->next=h;
	return h;
}
//创建循环单链表
 BookList * InputList(BookList *h){
 	BookList *s,*r;
	int num; 
	r=h;
	printf("==============================创建图书信息==============================\n");
	printf("请输入图书的数量:\n");
	scanf("%d",&num);
	for(int i=0;i<num;i++){
		printf("请输入第%d个图书信息：\n",i+1);
		s=(BookList*)malloc(sizeof(BookList));//创建存储数据的新结点 
		printf("请输入图书编号：\n");
		scanf("%d",&s->data.bookID);
		printf("请输入图书名称：\n");
		scanf("%s",&s->data.bookName);
		printf("请输入图书价格：\n");
		scanf("%lf",&s->data.bookPrice);
		r->next=s;
		r=s;
	}
	r->next=h;
    printf("创建成功！\n");
	return h;   //为啥返回h不返回的是r 
 }
 //输出图书信息 
void OutputList(BookList *L){
	int i=0;
	printf("==============================输出图书信息==============================\n");
	printf("图书编号  图书名称  图书价格\n");
	BookList *p,*d;
	p=L->next;
	while(p->next!=L->next){
		printf("      %d        %s       %.2lf\n", p->data.bookID, p->data.bookName, p->data.bookPrice);
		p=p->next;
	}
	printf("\n");
}
//增加图书信息表
int InsertList(BookList *L){
	printf("==============================增加图书信息==============================\n");
	BookList *p,*s;
	int num,j=0;
	p=L->next;
	printf("请输入新增数据的位置：\n");
	scanf("%d",&num);
	while(p!=L&&j<num-1){
		p=p->next;
		j++;
	}
	if(j!=num-1){
		printf("插入位置不存在\n");
		return 0;
	}
	
	s=(BookList*)malloc(sizeof(BookList));
	printf("请输入图书编号：\n");
	scanf("%d",&s->data.bookID);
	printf("请输入图书名称：\n");
	scanf("%s",&s->data.bookName);
	printf("请输入图书价格：\n");
	scanf("%lf",&s->data.bookPrice);
	s->next=p->next;
	p->next=s;
	printf("新增成功\n");
	return 1;
}
//删除图书信息表
int DeleteList(BookList *L){
	BookList *r,*pre;
	int num,j=0;
	r=L->next;
	printf("==============================删除图书信息==============================\n");
	printf("请输入删除的图书编号：\n");
	scanf("%d",&num);
	while(r!=L){
		if(r->data.bookID==num){		
			pre->next=r->next;
			free(r);
			printf("删除成功\n"); 
			return 1;
		}
		pre=r;
		r=r->next;
	}
	return 0;
}
//修改图书信息表
int UpdateList(BookList *L){
	BookList *pre,*r;
	int num;
	r=L->next;
	printf("==============================修改图书信息==============================\n");
	printf("请输入修改的图书编号：\n");
	scanf("%d",&num);
	while(r!=L){
		if(r->data.bookID==num){
			printf("请输入图书编号：\n");
			scanf("%d",&r->data.bookID);
			printf("请输入图书名称：\n");
			scanf("%s",&r->data.bookName);
			printf("请输入图书价格：\n");
			scanf("%lf",&r->data.bookPrice);
			return 1;
		}
		r=r->next;
	}
	return 0;
}
// 查找图书信息表 
int SelectList(BookList *L){
	BookList *r,*pre;
	int  num;
	r=L->next;
	printf("==============================查找图书信息==============================\n");
	printf("请输入查找的图书编号：\n");
	scanf("%d",&num);
	while(r!=L){
		if(r->data.bookID==num){
			printf("图书编号  图书名称  图书价格\n");
			printf("      %d        %s       %.2lf\n", r->data.bookID, r->data.bookName, r->data.bookPrice);
			return 1;
		}
		r=r->next;
	}
	printf("sorry，不存在此图书\n");
	return 0; 
}
int main(){
	BookList *h;
	BookList *L=NULL;
	DataType e;
	int n,flag=0;
	do{
		printf("********************************************\n");
		printf("*           1.创建图书信息表               *\n");
        printf("*           2.输入图书信息表               *\n");
    	printf("*           3.输出图书信息表               *\n");
   		printf("*           4.增加图书信息表               *\n");
    	printf("*           5.删除图书信息表               *\n");
    	printf("*           6.修改图书信息表               *\n");
    	printf("*           7.查找图书信息表               *\n");
    	printf("*           0.退出系统                     *\n");
    	printf("********************************************\n");
        printf("请根据提示操作！\n");
    	scanf("%d",&n);
    	switch(n){
    		case 1:
    			h=InitList(h);
    			printf("初始化成功！！\n");
    		break;
    		case 2:
    			L=InputList(h);
			break; 
			case 3:
				OutputList(L);
			break; 
			case 4:
				InsertList(L);
			break;
			case 5:
				DeleteList(L);
			break;
			case 6:
				UpdateList(L);
			break;
			case 7:
				SelectList(L);
			break;
			case 0:
				flag=1;
			break;
			default:
				printf("请输入正确的图书操作类型\n");
			break;
		}
	}while(flag!=1);
}

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