typedef struct item
{item *prev = NULL;item *next = NULL;char name[20];int math;int cna;int eng;int avg;bool flag = false;//有内容标志，可以忽略掉第一个数据得问题
}date;

void additem()//增
{date *head;date *ptr;ptr = &first;while (true){if (ptr->flag == false)//该内存区域下没有数据{printf("name:\n");fflush(stdin);//清除缓存空间 否则gets_s会因为检测缓存空间的空字符而跳过gets_s(ptr->name);printf("Math:\n");scanf_s("%d", &ptr->math);printf("Chinese:\n");scanf_s("%d", &ptr->cna);printf("English:\n");scanf_s("%d", &ptr->eng);ptr->avg = (ptr->cna + ptr->eng + ptr->math) / 3;ptr->flag = true;printf("write succed!\n\n\n");break;}else//如果没有数据{if (ptr->next == NULL)//尚无开空间，开新空间{head = ptr;//记录前一个数据存储空间ptr->next = (date*)malloc(sizeof(date));//开辟一个存储空间ptr = ptr->next;ptr->next = NULL;//初始化部分变量ptr->prev = head;//记录上一个数据ptr->flag = false;}else{ptr = ptr->next;//还有数据只想下一个数据存储空间}}}
}

void display()
{date *ptr;ptr = &first;//指向第一个存储空间if (ptr->flag == false){printf("no data in the link list\n");return;}printf("***********************************************\n");printf("Name     Math     Chinese     English     AVG\n");while (true){printf("%-9s%-9d%-12d%-12d%-3d\n", ptr->name, ptr->math, ptr->cna, ptr->eng, ptr->avg);if (ptr->next == NULL)break;else ptr = ptr->next;}printf("**********************************************\n");
}

date* search()//查
{date *ptr;ptr = &first;//指向第一个存储空间char name[20];printf("name:\n");fflush(stdin);gets_s(name);while (true){if (strcmp(ptr->name, name) == 0)break;//找到结果结束遍历else if (ptr->next == NULL)///遍历结束未找到结果{printf("no date!\n");return NULL;}else ptr = ptr->next;}printf("check the information\n");printf("***********************************************\n");printf("Name     Math     Chinese     English     AVG\n");printf("%-9s%-9d%-12d%-12d%-3d\n", ptr->name, ptr->math, ptr->cna, ptr->eng, ptr->avg);printf("**********************************************\n\n");return ptr;
}

void modify()//改
{char k=0;date*ptr;ptr = search();printf("sure?(Y/N)\n");k=_getch();if (k == 'Y' || k == 'y'){printf("name:\n");fflush(stdin);gets_s(ptr->name);printf("Math:\n");scanf_s("%d",&ptr->math);printf("Chinese:\n");scanf_s("%d", &ptr->cna);printf("English:\n", &ptr->eng);scanf_s("%d", &ptr->eng);printf("modify complete!\n");}
}

void delitem()//删
{date *ptr;ptr = search();if (ptr == NULL)return;//没有搜寻到相关元素printf("Are you sure?(Y/N)\n");char key= _getch();if (key == 'Y' || key == 'y'){if (ptr->prev != NULL){ptr->prev->next = ptr->next;ptr->next->prev = ptr->prev;free(ptr);}else//如果是表头元素将其重新初始化即可{if (ptr->next != NULL){first = *ptr->next;first.prev = NULL;}else{printf("already no data in link list\n");first.flag = false;}}}}