16-将枚举量用作标签

6.5.1　将枚举量用作标签

程序清单6.11使用enum定义了一组相关的常量，然后在switch语句中使用这些常量。通常，cin无法识别枚举类型（它不知道程序员是如何定义它们的），因此该程序要求用户选择选项时输入一个整数。当switch语句将int值和枚举量标签进行比较时，将枚举量提升为int。另外，在while循环测试条件中，也会将枚举量提升为int类型。

程序清单6.11　enum.cpp

// enum.cpp -- using enum
#include <iostream>
// create named constants for 0 - 6
enum {red, orange, yellow, green, blue, violet, indigo};
int main()
{
    using namespace std;
    cout << "Enter color code (0-6): ";
    int code;
    cin >> code;
    while (code >= red && code <= indigo)
    {
        switch (code)
        {
            case red    : cout << "Her lips were red.\n"; break;
            case orange : cout << "Her hair was orange.\n"; break;
            case yellow : cout << "Her shoes were yellow.\n"; break;
            case green  : cout << "Her nails were green.\n"; break;
            case blue   : cout << "Her sweatsuit was blue.\n"; break;
            case violet : cout << "Her eyes were violet.\n"; break;
            case indigo : cout << "Her mood was indigo.\n"; break;
        }
        cout << "Enter color code (0-6): ";
        cin >> code;
    }
    cout << "Bye\n";
    return 0;
}

下面是该程序的输出：

Enter color code (0-6): 3
Her nails were green.
Enter color code (0-6): 5
Her eyes were violet.
Enter color code (0-6): 2
Her shoes were yellow.
Enter color code (0-6): 8
Bye