palindrome.cpp:3:44: warning: use of 'auto' in parameter declaration only available with '-fconcepts'
3 | void expand(string str, int low, int high, auto& set)
| ^~~~
palindrome.cpp: In function 'int main()':
palindrome.cpp:30:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
30 | for (int i = 0; i < str.length(); i++)
| ~~^~~~~~~~~~~~~~
palindrome.cpp: In instantiation of 'void expand(std::string, int, int, auto:1&) [with auto:1 = std::unordered_set<std::__cxx11::basic_string<char> >; std::string = std::__cxx11::basic_string<char>]':
palindrome.cpp:32:30: required from here
palindrome.cpp:5:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
5 | while (low >= 0 && high < str.length() && str[low] == str[high])
| ~~~~~^~~~~~~~~~~~~~