/in/foo.cc: In function 'bool imp(std::__cxx11::string)':
/in/foo.cc:6:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int j = 0; j <= s.length(); j++){
                 ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'bool n16(std::__cxx11::string)':
/in/foo.cc:12:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int j = 0; j <= s.length(); j++){
                 ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'bool n10(std::__cxx11::string)':
/in/foo.cc:18:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int j = 0; j <= s.length(); j++){
                 ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'bool n8(std::__cxx11::string)':
/in/foo.cc:24:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int j = 0; j <= s.length(); j++){
                 ~~^~~~~~~~~~~~~