/in/foo.cc: In function 'int main()':
/in/foo.cc:9:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < s.size(); i++)
                  ~~^~~~~~~~~~
/in/foo.cc:12:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while (s[i] == s[j] && j < s1.size())
                          ~~^~~~~~~~~~~
/in/foo.cc:14:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (j == s1.size())
       ~~^~~~~~~~~~~~
/in/foo.cc:11:14: warning: unused variable 'f' [-Wunused-variable]
   int j = 0, f = 0;
              ^