/in/foo.cc: In function 'bool f(std::__cxx11::string)':
/in/foo.cc:25:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < ip.length(); i++)
                  ~~^~~~~~~~~~~~~
/in/foo.cc:35:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < ip.length(); i++)
                  ~~^~~~~~~~~~~~~
/in/foo.cc:38:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (i + 1 == ip.length()&&(ip[i]>='0'&&ip[i]<='9'))
       ~~~~~~^~~~~~~~~~~~~~
/in/foo.cc:40:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (ip[i] == '.' || i+1 == ip.length())
                       ~~~~^~~~~~~~~~~~~~