if ( userResponse != 'b' && userResponse != 'B' ) { // add more && as needed
cout << "This is not a valid answer, try again" << endl;
}
You can halve the number of tests by converting case to begin
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userResponse = toupper(userResponse)
if ( userResponse != 'B' ) { // add more &&, with just the capitals.
cout << "This is not a valid answer, try again" << endl;
}
Or create a search string
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if ( string("BSDbsd").find(userResponse) == std::string::npos ) {
cout << "This is not a valid answer, try again" << endl;
}