I intend to accept all of the following answers:

• y
• Y
• yes
• YES
• Yes
• plus mixtures, such as yeS, yES, which I didn’t intend to accept but it’s a consequence of my code
• the same applies to No and its variants

#include <iostream>     // std::cout, std::cin #include <string>       // std::string #include <algorithm>    // std::transform  int main() {      bool answer_valid = false;     std::string answer;      do     {         std::cout << "Should the password include digits? [Y/n] ";         std::cin >> answer;          std::transform(answer.begin(), answer.end(), answer.begin(), ::tolower);          answer_valid =             (answer == "y") ||             (answer == "n") ||             (answer == "yes") ||             (answer == "no");      } while (!answer_valid);      return 0;  } 

It works flawlessly, or it seems so. Is there better approach?