第10课 · 结构体

int   num;            // 学号
char  name[20];       // 姓名
char  sex;            // 性别
int   age;            // 年龄
float score;          // 成绩
char  addr[30];       // 地址

struct 结构体名
{ 成员表列 };

struct Student
{ int num;            // 学号为整型
  char name[20];      // 姓名为字符串
  char sex;           // 性别为字符型
  int age;            // 年龄为整型
  float score;        // 成绩为实型
  char addr[30];      // 地址为字符串
};                    // 注意最后有一个分号

struct Date                 // 先声明一个结构体类型 struct Date
{ int month;                // 月
  int day;                  // 日
  int year;                 // 年
};

struct Student              // 再声明一个结构体类型 struct Student
{ int num;
  char name[20];
  char sex;
  int age;
  struct Date birthday;     // 成员 birthday 属于 struct Date 类型
  char addr[30];
};

struct Student student1, student2;

struct Student
{ int num;
  char name[20];
  char sex;
  int age;
  float score;
  char addr[30];
} student1, student2;      // 花括号后直接跟变量名

struct
{ int num;
  char name[20];
  ...
} student1, student2;      // 连 Student 这个名字都不起

struct Student;              // ❌ 光写这一句不算定义完，没有成员表
student1.num = 101;          // ❌ 没定义 student1
Student s;                   // ❌ 类型名是 struct Student，不能只写 Student（除非用了 typedef）

struct Student a = {10101, "Li Lin", 'M', "123 Beijing Road"};

struct Student b = {.name = "Zhang Fang"};    // 成员名前的 . 是成员运算符

结构体变量名.成员名

student1.num = 10010;         // 把 10010 写进 student1 的 num 格
student2.score = student1.score;
sum = student1.score + student2.score;
student1.age++;               // 等价于 (student1.age)++，不是先给 age 自加

student1.num                  // 变量 student1 中的成员 num
student1.birthday.month       // 变量 student1 中成员 birthday 中的成员 month

student1 = student2;          // 前提：两者类型相同

printf("%s\n", student1);                 // ❌ 错！不能输出整个结构体
scanf("%d,%s,%c", &student1);             // ❌ 错！不能整体读入

scanf("%d", &student1.num);      // 输入 student1.num 的值
printf("%p", &student1);         // 输出 student1 的起始地址

// 写法①：声明类型的同时定义数组
struct 结构体名
{ 成员表列 } 数组名[数组长度];

// 写法②：先声明类型，再定义数组（推荐）
struct Person leader[3];        // leader 是结构体数组名

struct Person leader[3] = {"Li", 0, "Zhang", 0, "Sun", 0};
// 更清楚的写法：
struct Person leader[3] = {{"Li", 0}, {"Zhang", 0}, {"Sun", 0}};

leader[0].name        // 第 0 张表的姓名格
leader[j].count++     // 第 j 张表的票数加 1

struct Student *pt;      // pt 可以指向 struct Student 类型的变量或数组元素

(++p)->num      // 先 p 自加 1（指向下一个元素），再取 num
(p++)->num      // 先取当前 p 的 num，然后 p 自加 1

p = stu[0].name;                  // ❌ 类型不匹配，name 是 char*，p 是 struct Student*
p = (struct Student *)stu[0].name; // 语法上能过，但语义很怪，不要这么写

struct Student
{ long num;
  float score;
  struct Student *next;      // next 是指针变量，指向 struct Student 类型
};

union Data
{ int i;
  char ch;
  float f;
} a, b, c;              // 声明类型的同时定义变量

   printf("%d", a.i);   // 输出 97
   printf("%c", a.ch);  // 输出字符 'a'（97 正好是 'a' 的 ASCII 码）
   printf("%f", a.f);   // 输出 0.000000（按浮点规则解释这串二进制）

   union Data a = {16};          // ✅ 只给第 1 个成员
   union Data a = {16, 'a', 1.5}; // ❌ 不能初始化 3 个，它们共用一段内存

enum Weekday {sun, mon, tue, wed, thu, fri, sat};
enum Weekday workday, weekend;      // 枚举类型  枚举变量

workday = mon;        // ✅ 正确，mon 是指定的枚举常量之一
workday = sun;        // ✅ 正确
workday = monday;     // ❌ 错，monday 不是指定的枚举常量之一

   enum Weekday {sun = 7, mon = 1, tue, wed, thu, fri, sat};
   // sun=7, mon=1, tue=2, wed=3, thu=4, fri=5, sat=6

typedef int Integer;          // ① 简单类型起别名
typedef struct
{ int month; int day; int year; } Date;   // ② 结构体类型起别名
typedef int Num[100];         // ③ 数组类型起别名：Num a; 等于 int a[100];
typedef char *String;         // ④ 指针类型起别名：String p, s[10];

#include <stdio.h>
int main()
{ struct Student
  { long int num;
    char name[20];
    char sex;
    char addr[20];
  } a = {10101, "Li Lin", 'M', "123 Beijing Road"};   // 定义结构体变量 a 并初始化
  printf("NO.:%ld\nname:%s\nsex:%c\naddress:%s\n",
         a.num, a.name, a.sex, a.addr);
  return 0;
}

NO.:10101
name:Li Lin
sex:M
address:123 Beijing Road

#include <stdio.h>
int main()
{ struct Student
  { int num;
    char name[20];
    float score;
  } student1, student2;
  scanf("%d%s%f", &student1.num, student1.name, &student1.score);
  scanf("%d%s%f", &student2.num, student2.name, &student2.score);
  printf("The higher score is:\n");
  if (student1.score > student2.score)
      printf("%d %s %6.2f\n", student1.num, student1.name, student1.score);
  else if (student1.score < student2.score)
      printf("%d %s %6.2f\n", student2.num, student2.name, student2.score);
  else
  { printf("%d %s %6.2f\n", student1.num, student1.name, student1.score);
    printf("%d %s %6.2f\n", student2.num, student2.name, student2.score);
  }
  return 0;
}

#include <string.h>
#include <stdio.h>
struct Person
{ char name[20];        // 候选人姓名
  int count;            // 候选人得票数
} leader[3] = {"Li", 0, "Zhang", 0, "Sun", 0};   // 定义结构体数组并初始化

int main()
{ int i, j;
  char leader_name[20];                    // 定义字符数组
  for (i = 1; i <= 10; i++)
  { scanf("%s", leader_name);              // 输入所选候选人姓名
    for (j = 0; j < 3; j++)
        if (strcmp(leader_name, leader[j].name) == 0)
            leader[j].count++;
  }
  printf("\nResult:\n");
  for (i = 0; i < 3; i++)
      printf("%5s:%d\n", leader[i].name, leader[i].count);
  return 0;
}

Result:
   Li:4
Zhang:2
  Sun:3

#include <stdio.h>
struct Student
{ int num;
  char name[20];
  float score;
};

int main()
{ struct Student stu[5] = {{10101, "Zhang", 78}, {10103, "Wang", 98.5},
                            {10106, "Li", 86}, {10108, "Ling", 73.5},
                            {10110, "Sun", 100}};    // 定义结构体数组并初始化
  struct Student temp;                               // 交换时的临时变量
  const int n = 5;                                   // 定义常变量
  int i, j, k;
  printf("The order is:\n");
  for (i = 0; i < n - 1; i++)
  { k = i;
    for (j = i + 1; j < n; j++)
        if (stu[j].score > stu[k].score) k = j;      // 进行成绩的比较
    temp = stu[k]; stu[k] = stu[i]; stu[i] = temp;   // stu[k] 和 stu[i] 元素互换
  }
  for (i = 0; i < n; i++)
      printf("%6d %8s %6.2f\n", stu[i].num, stu[i].name, stu[i].score);
  printf("\n");
  return 0;
}

The order is:
 10110      Sun 100.00
 10103     Wang  98.50
 10106       Li  86.00
 10101    Zhang  78.00
 10108     Ling  73.50

#include <stdio.h>
#include <string.h>
int main()
{ struct Student
  { long num;
    char name[20];
    char sex;
    float score;
  };
  struct Student stu1;              // 定义 struct Student 类型的变量 stu1
  struct Student *p;                // 定义指向 struct Student 类型数据的指针变量 p
  p = &stu1;                        // p 指向 stu1
  stu1.num = 10101;                 // 对结构体变量的成员赋值
  strcpy(stu1.name, "Li Lin");      // 用字符串复制函数给 stu1.name 赋值
  stu1.sex = 'M';
  stu1.score = 89.5;
  printf("No.%ld\nname:%s\nsex:%c\nscore:%5.1f\n",
         stu1.num, stu1.name, stu1.sex, stu1.score);
  printf("\nNo.%ld\nname:%s\nsex:%c\nscore:%5.1f\n",
         (*p).num, (*p).name, (*p).sex, (*p).score);
  return 0;
}

#include <stdio.h>
struct Student
{ int num;
  char name[20];
  char sex;
  int age;
};
struct Student stu[3] = {{10101, "Li Lin", 'M', 18},
                         {10102, "Zhang Fang", 'M', 19},
                         {10104, "Wang Min", 'F', 20}};

int main()
{ struct Student *p;
  printf(" No.   Name                sex age\n");
  for (p = stu; p < stu + 3; p++)
      printf("%5d %-20s %2c %4d\n", p->num, p->name, p->sex, p->age);
  return 0;
}

 No.   Name                sex age
10101 Li Lin                M   18
10102 Zhang Fang            M   19
10104 Wang Min              F   20

#include <stdio.h>
#define N 3
struct Student
{ int num;
  char name[20];
  float score[3];
  float aver;
};

int main()
{ void input(struct Student stu[]);              // 函数声明
  struct Student max(struct Student stu[]);      // 函数声明
  void print(struct Student stu);                // 函数声明
  struct Student stu[N], *p = stu;               // 定义结构体数组和指针
  input(p);                                      // 调用 input 函数
  print(max(p));                                 // 用 max 的返回值作 print 的实参
  return 0;
}

void input(struct Student stu[])                 // 定义 input 函数
{ int i;
  printf("请输入各学生的信息：学号、姓名、3门课成绩：\n");
  for (i = 0; i < N; i++)
  { scanf("%d %s %f %f %f", &stu[i].num, stu[i].name,
          &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);
    stu[i].aver = (stu[i].score[0] + stu[i].score[1] + stu[i].score[2]) / 3.0;
  }
}

struct Student max(struct Student stu[])         // 定义 max 函数
{ int i, m = 0;
  for (i = 0; i < N; i++)
      if (stu[i].aver > stu[m].aver) m = i;
  return stu[m];                                 // 返回包含该生信息的结构体元素
}

void print(struct Student stud)                  // 定义 print 函数
{ printf("\n成绩最高的学生是：\n");
  printf("学号:%d\n姓名:%s\n三门课成绩:%5.1f,%5.1f,%5.1f\n平均成绩:%6.2f\n",
         stud.num, stud.name, stud.score[0], stud.score[1], stud.score[2], stud.aver);
}

请输入各学生的信息：学号、姓名、3门课成绩：
10101 Li 78 89 98
10103 Wang 98.5 87 69
10106 Sun 88 76.5 89

成绩最高的学生是：
学号:10101
姓名:Li
三门课成绩: 78.0, 89.0, 98.0
平均成绩: 88.33

#include <stdio.h>
struct Student
{ int num;
  float score;
  struct Student *next;
};

int main()
{ struct Student a, b, c, *head, *p;
  a.num = 10101; a.score = 89.5;
  b.num = 10103; b.score = 90;
  c.num = 10107; c.score = 85;
  head = &a;            // 头指针指向 a 结点
  a.next = &b;          // a 的 next 指向 b
  b.next = &c;          // b 的 next 指向 c
  c.next = NULL;        // c 的 next 不指向任何结点，链表结束
  p = head;
  do
  { printf("%ld %5.1f\n", p->num, p->score);
    p = p->next;        // p 移到下一结点
  } while (p != NULL);
  return 0;
}

#include <stdio.h>
struct
{ int num;
  char name[10];
  char sex;
  char job;
  union
  { int clas;                 // class 是 C++ 关键字，VC++ 下改用 clas
    char position[10];
  } category;                 // category 是共用体变量
} person[2];                  // 定义结构体数组 person，有两个元素

int main()
{ int i;
  for (i = 0; i < 2; i++)
  { printf("please enter the data of person:\n");
    scanf("%d %s %c %c", &person[i].num, person[i].name,
          &person[i].sex, &person[i].job);
    if (person[i].job == 's')
        scanf("%d", &person[i].category.clas);          // 学生，输入班级
    else if (person[i].job == 't')
        scanf("%s", person[i].category.position);       // 教师，输入职务
    else
        printf("Input error!\n");
  }
  printf("\nNo.  name      sex job class/position\n");
  for (i = 0; i < 2; i++)
  { if (person[i].job == 's')
        printf("%-6d%-10s%-4c%-4c%-10d\n", person[i].num, person[i].name,
               person[i].sex, person[i].job, person[i].category.clas);
    else
        printf("%-6d%-10s%-4c%-4c%-10s\n", person[i].num, person[i].name,
               person[i].sex, person[i].job, person[i].category.position);
  }
  return 0;
}

please enter the data of person:
101 Li f s 501
please enter the data of person:
102 Wang m t prof

No.  name      sex job class/position
101  Li        f   s   501
102  Wang      m   t   prof

#include <stdio.h>
int main()
{ enum Color {red, yellow, blue, white, black};   // 声明枚举类型 enum Color
  enum Color i, j, k, pri;                         // 定义枚举变量
  int n, loop;
  n = 0;
  for (i = red; i <= black; i++)                   // 外循环：第 1 个球
    for (j = red; j <= black; j++)                 // 中循环：第 2 个球
      if (i != j)                                  // 如果二球不同色
      { for (k = red; k <= black; k++)             // 内循环：第 3 个球
          if ((k != i) && (k != j))                // 如果 3 球不同色
          { n = n + 1;                             // 符合条件的次数加 1
            printf("%-4d", n);                     // 输出第几个组合
            for (loop = 1; loop <= 3; loop++)      // 先后对 3 个球分别处理
            { switch (loop)
              { case 1: pri = i; break;            // loop=1，取第 1 球的颜色
                case 2: pri = j; break;            // loop=2，取第 2 球的颜色
                case 3: pri = k; break;            // loop=3，取第 3 球的颜色
                default: break;
              }
              switch (pri)                         // 根据球的颜色输出相应文字
              { case red:    printf("%-10s", "red");    break;
                case yellow: printf("%-10s", "yellow"); break;
                case blue:   printf("%-10s", "blue");   break;
                case white:  printf("%-10s", "white");  break;
                case black:  printf("%-10s", "black");  break;
                default: break;
              }
            }
            printf("\n");
          }
      }
  printf("\ntotal:%5d\n", n);
  return 0;
}

#include <stdio.h>
struct Date
{ int year;
  int month;
  int day;
};

int main()
{ struct Date d;
  int days[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  int i, sum = 0;
  printf("请输入年 月 日：");
  scanf("%d %d %d", &d.year, &d.month, &d.day);
  if ((d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0)
      days[2] = 29;                       // 闰年 2 月 29 天
  for (i = 1; i < d.month; i++)
      sum += days[i];                     // 累加本月之前的整月
  sum += d.day;                           // 加上当月天数
  printf("%d年%d月%d日是该年的第%d天\n", d.year, d.month, d.day, sum);
  return 0;
}

#include <stdio.h>
struct Date
{ int year;
  int month;
  int day;
};

int days(struct Date d)
{ int daysOfMonth[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  int i, sum = 0;
  if ((d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0)
      daysOfMonth[2] = 29;
  for (i = 1; i < d.month; i++)
      sum += daysOfMonth[i];
  return sum + d.day;
}

int main()
{ struct Date d;
  printf("请输入年 月 日：");
  scanf("%d %d %d", &d.year, &d.month, &d.day);
  printf("该日是本年的第 %d 天\n", days(d));
  return 0;
}

#include <stdio.h>
#define N 5
struct Student
{ int num;
  char name[20];
  float score[3];
};

void print(struct Student stu[])
{ int i;
  printf("%-8s%-12s%-8s%-8s%-8s\n", "num", "name", "score1", "score2", "score3");
  for (i = 0; i < N; i++)
      printf("%-8d%-12s%-8.1f%-8.1f%-8.1f\n", stu[i].num, stu[i].name,
             stu[i].score[0], stu[i].score[1], stu[i].score[2]);
}

int main()
{ struct Student stu[N];
  int i;
  printf("请输入%d个学生的学号、姓名、3门课成绩：\n", N);
  for (i = 0; i < N; i++)
      scanf("%d %s %f %f %f", &stu[i].num, stu[i].name,
            &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);
  print(stu);
  return 0;
}

#include <stdio.h>
#define N 5
struct Student
{ int num;
  char name[20];
  float score[3];
};

void input(struct Student stu[])
{ int i;
  printf("请输入%d个学生的学号、姓名、3门课成绩：\n", N);
  for (i = 0; i < N; i++)
      scanf("%d %s %f %f %f", &stu[i].num, stu[i].name,
            &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);
}

void print(struct Student stu[])
{ int i;
  for (i = 0; i < N; i++)
      printf("%-8d%-12s%-8.1f%-8.1f%-8.1f\n", stu[i].num, stu[i].name,
             stu[i].score[0], stu[i].score[1], stu[i].score[2]);
}

int main()
{ struct Student stu[N];
  input(stu);
  print(stu);
  return 0;
}

#include <stdio.h>
#define N 10
struct Student
{ int num;
  char name[20];
  float score[3];
  float aver;
};

int main()
{ struct Student stu[N], max;
  int i;
  float sum = 0;
  printf("请输入%d个学生的学号、姓名、3门课成绩：\n", N);
  for (i = 0; i < N; i++)
  { scanf("%d %s %f %f %f", &stu[i].num, stu[i].name,
          &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);
    stu[i].aver = (stu[i].score[0] + stu[i].score[1] + stu[i].score[2]) / 3.0f;
    sum += stu[i].aver;
  }
  max = stu[0];                              // 先假设第 0 个最高
  for (i = 1; i < N; i++)
      if (stu[i].aver > max.aver) max = stu[i];   // 整张表复制过去
  printf("3门课程总平均成绩：%.2f\n", sum / N);
  printf("最高分学生：%d %s %.1f %.1f %.1f 平均%.2f\n",
         max.num, max.name, max.score[0], max.score[1], max.score[2], max.aver);
  return 0;
}

#include <stdio.h>
#include <stdlib.h>
#define N 13
struct Person
{ int num;
  struct Person *next;
};

int main()
{ struct Person *head = NULL, *tail = NULL, *p, *prev;
  int i, count = 0;
  for (i = 1; i <= N; i++)                       // 建 13 个结点
  { p = (struct Person *)malloc(sizeof(struct Person));
    p->num = i;
    p->next = NULL;
    if (head == NULL) { head = p; tail = p; }
    else { tail->next = p; tail = p; }
  }
  tail->next = head;                             // 首尾相接，围成一圈
  p = head;
  prev = tail;
  while (p->next != p)                           // 只剩一个人时结束
  { count++;
    if (count == 3)
    { prev->next = p->next;                      // 报到 3，摘掉 p 结点
      p = p->next;
      count = 0;
    }
    else
    { prev = p;
      p = p->next;
    }
  }
  printf("最后留在圈子里的是原来的第 %d 号\n", p->num);
  free(p);
  return 0;
}

struct Student
{ long num;
  float score;
  struct Student *next;
};
int n;

struct Student *del(struct Student *head, long num)
{ struct Student *p1, *p2;
  if (head == NULL)
  { printf("链表为空！\n"); return head; }
  p1 = head;
  while (num != p1->num && p1->next != NULL)     // 找目标结点
  { p2 = p1;
    p1 = p1->next;
  }
  if (num == p1->num)                            // 找到了
  { if (p1 == head) head = p1->next;             // 删的是头结点
    else p2->next = p1->next;                    // 删的是中间/尾结点
    printf("删除：%ld\n", num);
    n--;
    free(p1);
  }
  else printf("没找到：%ld\n", num);
  return head;
}

struct Student *insert(struct Student *head, struct Student *stud)
{ struct Student *p0, *p1, *p2;
  p0 = stud;
  if (head == NULL)                              // 空表：直接当表头
  { head = p0; p0->next = NULL; }
  else
  { p1 = head;
    while (p0->num > p1->num && p1->next != NULL) // 找插入位置
    { p2 = p1;
      p1 = p1->next;
    }
    if (p0->num <= p1->num)
    { if (p1 == head) { head = p0; p0->next = p1; }   // 插在表头前
      else { p2->next = p0; p0->next = p1; }          // 插在 p2 和 p1 之间
    }
    else { p1->next = p0; p0->next = NULL; }          // 插在表尾
  }
  n++;
  return head;
}

#include <stdio.h>
#include <stdlib.h>
#define LEN sizeof(struct Student)
struct Student
{ long num;
  float score;
  struct Student *next;
};
int n;

struct Student *creat(void)
{ struct Student *head = NULL, *p1, *p2;
  n = 0;
  p1 = p2 = (struct Student *)malloc(LEN);
  scanf("%ld,%f", &p1->num, &p1->score);
  while (p1->num != 0)
  { n++;
    if (n == 1) head = p1;
    else p2->next = p1;
    p2 = p1;
    p1 = (struct Student *)malloc(LEN);
    scanf("%ld,%f", &p1->num, &p1->score);
  }
  p2->next = NULL;
  free(p1);                    // 最后多开的一个结点没用，释放掉
  return head;
}

void print(struct Student *head)
{ struct Student *p = head;
  printf("\nNow, These %d records are:\n", n);
  while (p != NULL)
  { printf("%ld %5.1f\n", p->num, p->score);
    p = p->next;
  }
}

struct Student *del(struct Student *head, long num)
{ struct Student *p1, *p2;
  if (head == NULL) { printf("链表为空！\n"); return head; }
  p1 = head;
  while (num != p1->num && p1->next != NULL) { p2 = p1; p1 = p1->next; }
  if (num == p1->num)
  { if (p1 == head) head = p1->next; else p2->next = p1->next;
    n--; free(p1);
  }
  else printf("没找到：%ld\n", num);
  return head;
}

struct Student *insert(struct Student *head, struct Student *stud)
{ struct Student *p0 = stud, *p1, *p2;
  if (head == NULL) { head = p0; p0->next = NULL; }
  else
  { p1 = head;
    while (p0->num > p1->num && p1->next != NULL) { p2 = p1; p1 = p1->next; }
    if (p0->num <= p1->num)
    { if (p1 == head) { head = p0; p0->next = p1; }
      else { p2->next = p0; p0->next = p1; } }
    else { p1->next = p0; p0->next = NULL; }
  }
  n++;
  return head;
}

int main()
{ struct Student *head, stud;
  head = creat();
  print(head);
  printf("请输入要删除的学号：");
  scanf("%ld", &stud.num);
  head = del(head, stud.num);
  print(head);
  printf("请输入要插入的学号、成绩：");
  scanf("%ld,%f", &stud.num, &stud.score);
  stud.next = NULL;
  head = insert(head, &stud);
  print(head);
  return 0;
}

struct Student *merge(struct Student *a, struct Student *b)
{ struct Student *head = NULL, *tail = NULL, *p;
  while (a != NULL && b != NULL)
  { if (a->num <= b->num) { p = a; a = a->next; }
    else { p = b; b = b->next; }
    p->next = NULL;
    if (head == NULL) { head = p; tail = p; }
    else { tail->next = p; tail = p; }
  }
  p = (a != NULL) ? a : b;                 // 剩下的那截直接接到表尾
  if (head == NULL) head = p;
  else tail->next = p;
  return head;
}

struct Student *deleteSame(struct Student *a, struct Student *b)
{ struct Student *pa = a, *prev = NULL, *pb, *q;
  int found;
  while (pa != NULL)
  { found = 0;
    for (pb = b; pb != NULL; pb = pb->next)      // 在 b 中找同学号
        if (pb->num == pa->num) { found = 1; break; }
    if (found)
    { q = pa;
      if (prev == NULL) a = pa->next;            // 删的是头结点
      else prev->next = pa->next;                // 删中间/尾结点
      pa = pa->next;
      free(q);
    }
    else { prev = pa; pa = pa->next; }
  }
  return a;
}

#include <stdio.h>
#include <stdlib.h>
struct Student
{ long num;
  char name[20];
  char sex;
  int age;
  struct Student *next;
};

struct Student *delAge(struct Student *head, int age)
{ struct Student *p = head, *prev = NULL, *q;
  while (p != NULL)
  { if (p->age == age)
    { q = p;
      if (prev == NULL) head = p->next;
      else prev->next = p->next;
      p = p->next;
      free(q);
    }
    else { prev = p; p = p->next; }
  }
  return head;
}

int main()
{ struct Student *head = NULL, *tail = NULL, *p;
  long num; char name[20]; char sex; int age; int i, del_age;
  printf("输入 5 个结点（学号 姓名 性别 年龄）：\n");
  for (i = 0; i < 5; i++)
  { p = (struct Student *)malloc(sizeof(struct Student));
    scanf("%ld %s %c %d", &p->num, p->name, &p->sex, &p->age);
    p->next = NULL;
    if (head == NULL) { head = p; tail = p; }
    else { tail->next = p; tail = p; }
  }
  printf("输入要删除的年龄：");
  scanf("%d", &del_age);
  head = delAge(head, del_age);
  printf("删除后的链表：\n");
  for (p = head; p != NULL; p = p->next)
      printf("%ld %s %c %d\n", p->num, p->name, p->sex, p->age);
  return 0;
}

#include <stdio.h>
struct Student
{ int num; char name[10]; };
int main(void)
{ struct Student a = {101, "Li"}, b;
  b = a;
  b.num = 202;
  printf("%d %s\n", a.num, a.name);
  return 0;
}

#include <stdio.h>
struct Point { int x, y; };
int main(void)
{ struct Point a = {1, 2}, *p = &a;
  p->x = 10;
  (*p).y = 20;
  printf("%d %d\n", a.x, a.y);
  return 0;
}

#include <stdio.h>
struct S { int num; };
int main(void)
{ struct S s[3] = {{1}, {2}, {3}};
  struct S *p = s;
  printf("%d ", (p++)->num);
  printf("%d ", p->num);
  printf("%d\n", (++p)->num);
  return 0;
}

#include <stdio.h>
union Data { int i; char ch; };
int main(void)
{ union Data a;
  a.i = 65;
  printf("%d %c\n", a.i, a.ch);
  return 0;
}

#define N 3
struct Student
{ int num; char name[20]; float score[3]; float aver; };

/* 请在这里补全：struct Student max(struct Student *p) */

/* 补完之后，在 VS 里自己敲主函数验证，调用方式如下（不是让你抄，是让你敲）：
     struct Student stu[N] = {{1, "Li", {80, 90, 100}, 90},
                              {2, "Wang", {70, 75, 80}, 75},
                              {3, "Sun", {95, 92, 98}, 95}};
     struct Student m = max(stu);
     printf("%d %s %.2f\n", m.num, m.name, m.aver);
   预期输出：3 Sun 95.00
*/

// ❌ 错误示例（故意）：请找出两处错并改正
#include <stdio.h>
struct Student
{ int num;
  char name[20];
}                                  // ①
int main(void)
{ Student s = {1, "Li"};           // ②
  printf("%d %s\n", s.num, s.name);
  return 0;
}

// ❌ 错误示例（故意）：请找出错在哪并改正
#include <stdio.h>
struct Student
{ int num;
  char name[20];
};
int main(void)
{ struct Student s = {1, "Li"};
  printf("%s\n", s);               // 这里
  return 0;
}

// ❌ 错误示例（故意）：请找出错在哪并改正
#include <stdio.h>
struct Student
{ int num;
  char name[20];
};
int main(void)
{ struct Student s = {1, "Li"}, *p = &s;
  printf("%d\n", *p.num);          // 这里
  return 0;
}