c语言中枚举类型

#include <stdio.h>

enum a {x, y, z};

int main(void)
{
    printf("x = %d\n", x);
    printf("y = %d\n", y);
    printf("z = %d\n", z);
    
    return 0;
}

#include <stdio.h>

enum a {x = 888, y = 1000, z = 123};

int main(void)
{
    printf("x = %d\n", x);
    printf("y = %d\n", y);
    printf("z = %d\n", z);
    
    return 0;
}

#include <stdio.h>

enum animal {Dog, Cat, Monkey, Invalid};

void dog(void)
{
    puts("wang wang.");
}

void cat(void)
{
    puts("miao miao");
}

void monkey(void)
{
    puts("ji ji");
}

enum animal select(void)
{
    enum animal tmp;
    do
    {
        puts("0: dog  1: cat  2: monkey  3: quit.");
        printf("tmp = "); scanf("%d", &tmp);
    }
    while(tmp < Dog || tmp > Invalid);
    return tmp;
}

int main(void)
{
    enum animal a;
    do
    {
        switch(a = select())
        {
            case Dog: dog(); break;
            case Cat: cat(); break;
            case Monkey: monkey(); break;
        }
    }
    while(a != Invalid);
    return 0; 
}