Main.cc: In function ‘std::vector tokenize(const string&)’:
Main.cc:40:18: error: unable to find string literal operator ‘operator""s’ with ‘const char [7]’, ‘long unsigned int’ arguments
else if ("+-*^()"s.find(expr[pos]) != string::npos)
^~~~~~~~~
Main.cc:47:33: error: unable to find string literal operator ‘operator""s’ with ‘const char [23]’, ‘long unsigned int’ arguments
throw runtime_error("unexpected character: "s + expr[pos]);
^~~~~~~~~~~~~~~~~~~~~~~~~