/in/foo.cc: In function 'int main()':
/in/foo.cc:9:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if (k == str.size())
      ~~^~~~~~~~~~~~~
/in/foo.cc:17:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while (t < str.size() && str[t++] != '0');
          ~~^~~~~~~~~~~~
/in/foo.cc:28:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    while (t < str.size() && str[t++] == '0');
           ~~^~~~~~~~~~~~
/in/foo.cc:34:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int i = 1; i < str.size(); i++)
                    ~~^~~~~~~~~~~~