枚举

枚举 enum 

枚举 enum 也和int struct 一样，是一种数据类型。

在使用上enum有些类似struct ，在效果上和#define相同。

typedef enum Week
{
    Monday    = 1, 
    Tuesday   = 2, 
    Wednesday = 3, 
    Thursday  = 4, 
    Friday    = 5, 
    Saturday  = 6, 
    Sunday    = 7
}Weekday1,Weekday2;

比如上面这个例子，使用typedef定义了一个枚举类型Week，同时还用该类型声明了2个未初始化的变量Weekday1 Weekday2

这里要注意枚举里的成员，只能是整形，所以即便我们不赋初值，系统也会按照顺序给枚举里的类型自动赋值

比如：

typedef enum Week
{
    Monday = 1, 
    Tuesday   , 
    Wednesday , 
    Thursday  , 
    Friday    , 
    Saturday  , 
    Sunday    
}Weekday1,Weekday2;

这段代码的效果和上一个完全相同。

系统自动为后面的Tuesday 等成员按顺序+1赋了值。

接下来看一下如何给枚举里的成员赋值

首先不使用typdef，这里展现了4种赋值方式

#include <stdio.h>

enum Week
{
    Monday = 1, 
    Tuesday   , 
    Wednesday , 
    Thursday  , 
    Friday    , 
    Saturday  , 
    Sunday    
}
Weekday1 = Monday,Weekday2 = Tuesday,Weekday4;

int main()
{
    enum Week Weekday3 = Friday;
    int Weekday5 = Saturday;
    Weekday4 = Sunday;
    
    printf("Monday     = %d
",Weekday1);
    printf("Tuesday    = %d
",Weekday2);
    printf("Friday     = %d
",Weekday3);
    printf("Saturday   = %d
",Weekday5);
    printf("Sunday     = %d
",Weekday4);

    return 0;
}

输出结果如下：

接下来使用typedef

#include <stdio.h>

typedef enum Week　　//这个Week可以不写
{
    Monday = 1, 
    Tuesday   , 
    Wednesday , 
    Thursday  , 
    Friday    , 
    Saturday  , 
    Sunday    
}Weekday,Zhou;


int main()
{
    enum Week Weekday3 = Friday;
    int Weekday5       = Saturday;
    Weekday Weekday4   = Sunday;
    Zhou Weekday2      = Tuesday; 

//  printf("Monday     = %d
",Weekday1);
    printf("Tuesday    = %d
",Weekday2);
    printf("Wednesday  = %d
",Wednesday);
    printf("Friday     = %d
",Weekday3);
    printf("Saturday   = %d
",Weekday5);
    printf("Sunday     = %d
",Weekday4);

    return 0;
}

输出结果如下：

枚举变量(Monday、Tuesday等)只能为右值

不能使用这种方法将其赋值

Monday = 18;　　//错误的做法