有沒有更好的方式來格式化這個while循環？

Question

在我正在創建的程序中搜索潛在錯誤時，我得到了 「[錯誤] ISO C++禁止指針和整數[-fpermissive]之間的比較。」

錯誤來自我的while循環，其中我打算程序只接受來自用戶的以下輸入。現在，我正在考慮爲這個數組使用一個數組。

我該如何解決這個問題？如果有人有任何更多的細節，我很樂意通過展示我的內容來提供他們（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

的意見已經相當詳盡，所以我只是總結起來：

dimension是一個char，你不能比較字符串常量，因此錯誤。您應該改用std::string。

一旦你改變了這個問題，你仍然需要在cin讀取任何內容之前檢查用戶輸入。你應該反過來做。

如果您使用容器並嘗試在該容器中查找用戶輸入，那麼您的條件將更具可讀性。

因此，這將是這樣的：

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; 
    } 
}