案例标签不会减少为C中的整数常量？

Question

我正在开发一款游戏，我运行了我的代码并得到了错误“case label does not reduce to an integer constant”。我想我知道这意味着什么，但我该如何解决呢？这是我的代码：

#include<stdio.h>
#include<stdlib.h

int player_cash[3] = {50};
char job[][20] {
    'A',
    'B',
    'C',
    "Donate",
    "Go to work",
    "Exit"
};
int jobs;

int main()
{
    while(player_cash[0] > 0) {
        printf("Please type A, B, C, Donate, Go to work, or Exit\n");
        switch(jobs) {

            case 'A':
            player_cash[0]-=5;
            player_cash[1]+=5;
            printf("Cash=%i\n\n", player_cash[0]);
            continue;

            case 'B':
            player_cash[0]-=5;
            player_cash[2]+=5;
            printf("Cash=%i\n\n", player_cash[0]);
            continue;

            case 'C':
            player_cash[0]-=5;
            player_cash[3]+=5;
            printf("Cash=%i\n\n", player_cash[0]);
            continue;

            case "Donate":
            player_cash[0]-=15; //Error here
            player_cash[1]+=5;
            player_cash[2]+=5;
            player_cash[3]+=5;
            printf("Cash donated\n\n");
            printf("Cash=%i\n\n", player_cash[0]);
            continue;

            case "Go to work":
            player_cash[0]+=10; //Error here
            printf("Work done\n\n");
            printf("Cash=%i\n\n", player_cash[0]);
            continue;

            case "Exit":
            printf("Thanks for playing!\n\n"); //Error here
            break;

            default:
            printf("Does not compute");
            continue;
        }
    }
        getchar();
        return 0;
}

所以，我希望用户做的是输入其中一个选项，然后执行与之对应的操作。我该如何解决这个问题？

Answer 1

您不能将字符串用作case 表达式：

case "Donate":

只能使用整数表达式，例如case 'A': 可以。

从概念上讲，您有问题：jobs 是 int，并且您正在测试字符串。如果您想允许用户输入字符串（多于一个字符），您需要保留一个字符串变量，并使用fgets 之类的东西来获取完整的输入行。

Answer 2

您的一些大小写标签是字符（键入char，用's 表示）。这些 是 整数常量。

其他标签是字符串文字（用"表示），其有效类型为const char *。¹那些不是整数常量，不能使用以这种方式。

---

¹ 由于历史原因，它们通常可以像char * 一样使用，但不要尝试更改它们。否则。

Answer 3

您不能将字符串与 c 进行比较。 "hello" == "hello" 不会按预期工作。 switch 只对基本类型进行简单的 c 比较。

switch(jobs) {

        case 'A':
        player_cash[0]-=5;
        player_cash[1]+=5;
        printf("Cash=%i\n\n", player_cash[0]);
        continue;

        case 'B':
        player_cash[0]-=5;
        player_cash[2]+=5;
        printf("Cash=%i\n\n", player_cash[0]);
        continue;

        case 'C':
        player_cash[0]-=5;
        player_cash[3]+=5;
        printf("Cash=%i\n\n", player_cash[0]);
        continue;

        case 'D':
        player_cash[0]-=15; //Error here
        player_cash[1]+=5;
        player_cash[2]+=5;
        player_cash[3]+=5;
        printf("Cash donated\n\n");
        printf("Cash=%i\n\n", player_cash[0]);
        continue;

        case 'G':
        player_cash[0]+=10; //Error here
        printf("Work done\n\n");
        printf("Cash=%i\n\n", player_cash[0]);
        continue;

        case 'E':
        printf("Thanks for playing!\n\n"); //Error here
        break;

        default:
        printf("Does not compute");
        continue;
    }

由于您只读取了getch() 中的一个字符，您可以比较这个值。 （但要求用户只输入一个字母，因为他输入“Donate”，getch() 会先读取 D，返回，然后读取 o，等等。）

Answer 4

1. 您的作业数组的初始值设定项不一致（char 和 const char * 混合使用）

2. 您不能将字符串文字用作大小写标签，因为 char 指针不是编译时常量。使用整数：

   enum jobType
   {
       jobA,
       jobB,
       jobC,
       jobDonate,
       jobGoToWork,
       jobExit,
       /* marker */
       jobInvalid
   };
   
   enum jobType typeOfJob(const char* const name)
   {
       int i;
       for (i=jobA; i!=jobInvalid; ++i)
           if (0 == strcmp(jobNames[i], name))
               return i;
       return i;
   }
   

3. 另外，player_cash 短 1 个元素（并且在索引 [3] 处写入超出范围）

代码示例还展示了如何避免一般的 gets 错误，进行一些基本的行尾修剪和不区分大小写的比较（Windows 上的 stricmp，IIRC）：http://liveworkspace.org/code/227015a4e51126d55ca4eb1eea739b02

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int player_cash[4] = {50};

enum jobType
{
    jobA,
    jobB,
    jobC,
    jobDonate,
    jobGoToWork,
    jobExit,
    /* marker */
    jobInvalid
};

const char jobNames[][20] =
{
    "A",
    "B",
    "C",
    "Donate",
    "Go to work",
    "Exit"
};

enum jobType typeOfJob(const char* const name)
{
    int i;
    for (i=jobA; i!=jobInvalid; ++i)
#ifdef CASE_SENSITIVE
        if (0 == strcmp(jobNames[i], name))
#else
        if (0 == strcasecmp(jobNames[i], name))
#endif
            return i;
    return i;
}

const char* safer_gets()
{
    static char input[1024];
    char *p;
    const char* t;
    const char trimAt[] = "\r\n\t ";
    fgets(input, sizeof(input), stdin);

    for (t=trimAt; *t; ++t)
        while(p = strrchr(input, *t)) 
            *p = 0;

    return input;
}

int main()
{
    const char* input;
    while(player_cash[0] > 0)
    {
        printf("Please type A, B, C, Donate, Go to work, or Exit\n");
        input = safer_gets();

        switch(typeOfJob(input))
        {
        case jobA:
            player_cash[0]-=5;
            player_cash[1]+=5;
            printf("Cash=%i\n\n", player_cash[0]);
            continue;
        case jobB:
            player_cash[0]-=5;
            player_cash[2]+=5;
            printf("Cash=%i\n\n", player_cash[0]);
            continue;
        case jobC:
            player_cash[0]-=5;
            player_cash[3]+=5;
            printf("Cash=%i\n\n", player_cash[0]);
            continue;
        case jobDonate:
            player_cash[0]-=15; 
            player_cash[1]+=5;
            player_cash[2]+=5;
            player_cash[3]+=5;
            printf("Cash donated\n\n");
            printf("Cash=%i\n\n", player_cash[0]);
            continue;
        case jobGoToWork:
            player_cash[0]+=10;
            printf("Work done\n\n");
            printf("Cash=%i\n\n", player_cash[0]);
            continue;
        case jobExit:
            printf("Thanks for playing!\n\n");
            break;
        default:
            printf("Does not compute");
            continue;
        }
    }
    getchar();
    return 0;
}