/in/foo.cc: In function 'int main()':
/in/foo.cc:21:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |     for (int i = 0; i <= str.length(); i++)
      |                     ~~^~~~~~~~~~~~~~~
/in/foo.cc:24:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |         if(i == str.length() || str[i] == '+' || str[i] == '*')
      |            ~~^~~~~~~~~~~~~~~
/in/foo.cc:29:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |             if(i != str.length())
      |                ~~^~~~~~~~~~~~~~~