C语言中共用体和枚举的实现

union 类型名
{
    数据类型 成员变量1;
    数据类型 成员变量2;
    数据类型 成员变量3;
    数据类型 成员变量4;
    ...
}

// 方式1：定义后单独声明
union Data 
{
    int i;
    char c;
    float f;
};
union Data a, b;

// 方式2：定义时声明变量
union Data2 
{
    int x;
    double y;
} c, d;

// 方式3：匿名共用体（仅使用一次，无名称）
union 
{
    char ch;
    short s;
} e;

#include <stdio.h>

union DATA
{
    int a;
    char c;
};

int main()
{
    union DATA data;
    data.a = 0x12345678;
    if(0x78 == data.c)
    {
        printf("little end\n");
    }
    else
    {
        printf("big end\n");
    }
    return 0;                                                                 
}

//枚举值当常量值看，类型为整形(int)
enum 类型名 {枚举值1,枚举值2, 枚举值3,枚举值4 ,枚举值5, 枚举值6, ... };

//MON如果没有指定值，那么它的值就是0，后面枚举值就在一个的值的基础上+1
enum WEEK {MON, TUE, WED, THU, FRI, SAT, SUN};

//当然也可一给每个枚举值赋新值进去
enum WEEK {MON,TUE=3,WED=4,THU=5,FRI=6,SAT,SUN};

#include <stdio.h>

enum WEEK {MON, TUE, WED, THU, FRI, SAT, SUN};

typedef enum
{
	JAN,
	FEB,
	MARCH,
	APRI,
	MAY,
	JU,
	JULY,
}MONTH;

int main()
{
	enum WEEK week;
	MONTH mon = MAY;

	int num = 0;
	printf("input num (0~6):");
	scanf("%d", &num);
	week = num;

	switch(week)
	{
		case MON:
			printf("go to school\n");
			break;
		case TUE:
			printf("go to swim\n");
			break;
		case WED:
			printf("go to read\n");
			break;
		case THU:
			printf("go to study\n");
			break;
		case FRI:
			printf("go to pao dao\n");
			break;
		case SAT:
			printf("go to da wa\n");
			break;
		case SUN:
			printf("go to sleep\n");
			break;
		default:
			printf("I don't know\n");
	}
}