Can I convert a string to a char?

[CNerd2121]

I'm trying to make several functions in a class. The point of the first function is to get a single character, ensure that the user only typed in one character as well as ensure that it's an allowed character before returning whatever they typed in as a char

This is the code so far:

class UserInputHandler {
  char GetSingleCharacter() {
    std::string str;
    char letter;
    int i;
    i = (int)str.length();
    const std::string invalid_char_input_("Failure: Too many characters.");
    const std::string char_not_allowed_("Failure: Invalid character.");
    std::getline(std::cin, str);
    if (std::string::npos == str.find_first_not_of("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")) {
      if (i > 1) {
        std::cout << invalid_char_input_;
        letter = invalid_char_input_;
      } else {
        std::cout << str;
        letter = str;
      }
    } else {
      std::cout << char_not_allowed_;
      letter = char_not_allowed_;
    }
    return letter;
  }
};

int main() {
  UserInputHandler();
  return 0;
}

And this is the compile error:

$ make
/usr/bin/g++ -Wall -Wextra -g assignment_2.cpp  -o assignment_2
assignment_2.cpp: In member function ‘char UserInputHandler::GetSingleCharacter()’:
assignment_2.cpp:30:16: error: cannot convert ‘const string {aka const std::basic_string<char>}’ to ‘char’ in assignment
         letter = invalid_char_input_;
                ^
assignment_2.cpp:33:16: error: cannot convert ‘std::string {aka std::basic_string<char>}’ to ‘char’ in assignment
         letter = str;
                ^
assignment_2.cpp:37:14: error: cannot convert ‘const string {aka const std::basic_string<char>}’ to ‘char’ in assignment
       letter = char_not_allowed_;
              ^
makefile:10: recipe for target 'assignment_2' failed
make: *** [assignment_2] Error 1

I am required to return whatever they typed in as a char, but char is not compatible with ".length()" based on my past attempts, so I need a string. Is there any way I could convert it?

[LB]

I don't understand why you are trying to perform the assignments on lines 13 and 20 (lines 30 and 37 in your error messages). You're trying to assign error messages to a single character. Huh???

As for line 16 (line 33) if you know the string is at least one character long you can just access str[0]

[CNerd2121]

Well I can't return what they typed if it wasn't valid, but I need to return something. I tried making letter = "N/A", but that didn't work either.

[LB]

Continue to prompt the user until you get a valid response.

[CNerd2121]

Not allowed to do that. Is there a way to set the char to a blank space, maybe?

[Zhuge]

CNerd2121 wrote:

The point of the first function is to get a single character, ensure that the user only typed in one character as well as ensure that it's an allowed character before returning whatever they typed in as a char

And how do you want to ensure that? What if they type more than one? What do you want to return then? If you just want a blank space, you certainly could return that, but what's the reasoning behind not prompting until you get valid data here rather than in the code that is using this function?