/in/foo.cc: In function 'bool flag(std::string, std::string)':
/in/foo.cc:5:12: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    5 |     if(lena!=b.length()){
      |        ~~~~^~~~~~~~~~~~