有没有更好的方式来格式化这个while循环？

Question

在我正在创建的程序中搜索潜在错误时，我得到了 “[错误] ISO C++禁止指针和整数[-fpermissive]之间的比较。”

错误来自我的while循环，其中我打算程序只接受来自用户的以下输入。现在，我正在考虑为这个数组使用一个数组。

我该如何解决这个问题？如果有人有任何更多的细节，我很乐意通过展示我的内容来提供他们（截至最近）。

int main() // While using one of the three functions to make conversions, 
// the program will create the table based on following information. 
{ 
    char dimension; 
    double u1, u2; 
    int starting_value, ending_value, increment, startingUnitDigits, 
    endingUnitDigits; 
    cout << "-------------------------------------------------------------------------------------------------"; 
    cout << "Please answer the following questions as they appear."; 
    cout << "Check spelling, use correct abbreviation for units of measurement, and avoid negative values."; 
    cout << "-------------------------------------------------------------------------------------------------"; 
    cout << "Enter the dimensions from the following choices: length, mass and time. (i.e.: 'length,' 'Length')."; 
    while (!(dimension == "length" || dimension == "Length" || dimension == "mass" || dimension == "Mass" || dimension == "time" || dimension == "Time")) 
    { 
     cout << "----------------------------------------------------------------------------------------------------"; 
     cout << "Error! Input for Dimension, " << dimension << ", was either an invalid choice or typed incorrectly."; 
     cout << "Please know that this programs accepts length, mass, and time only!"; 
     cout << "----------------------------------------------------------------------------------------------------"; 
     cout << "Enter the dimensions from the following choices: length, mass and time. (i.e.: 'length,' 'Length')."; 
     cin >> dimension; 

Answer 1

的意见已经相当详尽，所以我只是总结起来：

dimension是一个char，你不能比较字符串常量，因此错误。您应该改用std::string。

一旦你改变了这个问题，你仍然需要在cin读取任何内容之前检查用户输入。你应该反过来做。

如果您使用容器并尝试在该容器中查找用户输入，那么您的条件将更具可读性。

因此，这将是这样的：

std::vector<std::string> correct_input{"Foo","foo","f00"}; 
while(true) { 
    std::string dimension; 
    std::cin >> dimension; 
    auto it = std::find(correct_input.begin(),correct_input.end(),dimension); 
    if (std::cin.fail() || it==correct_input.end()) { 
     // print error and continue to ask for input 
     std::cin.clear(); // clear possible error flags 
    } else { 
     // do something with input 
     break; 
    } 
}