#if 如何工作？ 我是否误解了#if~#endif 的形式？

Question

#include <stdio.h>
#include <iostream>
using namespace std;

typedef int LOCAL;
LOCAL JAPAN = 81;
LOCAL KOREA = 82;
LOCAL CHINA = 86;
LOCAL USER_LOCAL = CHINA;

#if (USER_LOCAL == KOREA || USER_LOCAL == JAPAN)
typedef char NAME[20];
#elif (USER_LOCAL == CHINA)
typedef char NAME[5];
#endif


int main()
{
    NAME playername;
    cin >> playername;

    cout << "Welcome, " << playername << "!";
}

I changed

LOCAL USER_LOCAL = CHINA;

to

LOCAL USER_LOCAL = 86;

I did this changing to similar forms.

then

typedef int LOCAL;
LOCAL KOREA = 82;
LOCAL JAPAN = 81;
LOCAL CHINA = 86;
LOCAL USER_LOCAL = 86;

#if (USER_LOCAL == 82 || USER_LOCAL == 81)
typedef char NAME[20];
#elif (USER_LOCAL == 86)
typedef char NAME[5];
#endif

The above code works what I intended.

but I want to use country names instead of numbers. Do I misunderstand how (#if ~ #endif) works?

Answer 1

In #if , you can only use values that have been initialized with #define . This should work as expected:

#define JAPAN 81
#define KOREA 82
#define CHINA 86
#define USER_LOCAL CHINA

#if (USER_LOCAL == KOREA || USER_LOCAL == JAPAN)
typedef char NAME[20];
#elif (USER_LOCAL == CHINA)
typedef char NAME[5];
#endif