foo.cc: In function ‘int _8to10(std::string)’:
foo.cc:13:18: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   13 |     for(int i=0;i<s.size();i++)ans=ans*8+s[i]-'0';
      |                 ~^~~~~~~~~