12. 结构 Structures

12.1 单一的结构

生日

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

int main()
{
  struct Date birth;//⭐️⭐️

  birth.month = 12;//⭐️⭐️
  birth.day = 28;//⭐️⭐️
  birth.year = 1987;//⭐️⭐️
  printf("My birth date is %d/%d/%d\n",
  birth.month,birth.day,birth.year % 100);

  return 0;
}

12.2 结构的数组

数据量更大，且遵循规律。比如，员工编号，员工姓名，工资

#include <stdio.h>
#define NUMRECS 5
struct PayRecord /* construct a global structure type */
{
  int id;
  char name[20];
  double rate;
};

int main()
{
  int i;
  struct PayRecord employee[NUMRECS] = {{32479, "Abrams, B.", 6.72},
                                        {33623, "Bohm, P.", 7.54},
                                        {34145, "Donaldson, S.", 5.56},
                                        {35987, "Ernst, T.", 5.43},
                                        {36203, "Gwodz, K.", 8.72}
                                      };

  for (i = 0; i < NUMRECS; i++)
    printf("%d %-20s %4.2f\n",
           employee[i].id,employee[i].name,employee[i].rate);

  return 0;
}

12.3 传递结构和返回结构

传递

#include <stdio.h>
struct Employee /* declare a global structure type */
{
  int idNum;
  double payRate;
  double hours;
};

double calcNet(struct Employee); /* function prototype */

int main()
{
  struct Employee emp = {6787, 8.93, 40.5};
  double netPay;

  netPay = calcNet(emp); /* pass copies of the values in emp */
  printf("The net pay of employee %d is $%6.2f\n",
                                          emp.idNum,netPay);

  return 0;
}

double calcNet(struct Employee temp)
/* temp is of data type struct Employee */
{
  return(temp.payRate * temp.hours);
}

(*pt).idNum 能用 pt->idNum 代替

#include <stdio.h>
struct Employee /* declare a global structure type */
{
  int idNum;
  double payRate;
  double hours;
};

double calcNet(struct Employee *); /* function prototype */

int main()
{
  struct Employee emp = {6787, 8.93, 40.5};
  double netPay;

  netPay = calcNet(&emp); /* pass an address*/
  printf("The net pay for employee %d is $%6.2f\n",
                                   emp.idNum, netPay);

  return 0;
}

double calcNet(struct Employee *pt) /* pt is a pointer to a */
{
  /* structure of Employee type */
  return(pt->payRate * pt->hours);
}

返回一个完整的结构给main()

#include <stdio.h>
struct Employee /* declare a global structure type */
{
  int idNum;
  double payRate;
  double hours;
};

struct Employee getValues(); /* function prototype */

int main()
{
  struct Employee emp;

  emp = getValues();
  printf("The employee id number is %d\n", emp.idNum);
  printf("The employee pay rate is $%5.2f\n", emp.payRate);
  printf("The employee hours are %5.2f\n", emp.hours);

  return 0;
}

struct Employee getValues()
{
  struct Employee newemp;
 
  newemp.idNum = 6789;
  newemp.payRate = 16.25;
  newemp.hours = 38.0;

  return (newemp);
}

12.4 联合union（略）

union是一种保留两个或多个变量在内存中相同区域的数据类型，这些变量可以是不同的数据类型。

union
{
  char key;
  int num;
  double price;
}