/in/foo.cc: In function 'int main()':
/in/foo.cc:13:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (i=0;i<s.length();i++)
           ~^~~~~~~~~~~
/in/foo.cc:26:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (i=0;i<s.length();i++)
            ~^~~~~~~~~~~
/in/foo.cc:46:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (i<=s.length();i>=0;i--)
        ~^~~~~~~~~~~~
/in/foo.cc:46:9: warning: value computed is not used [-Wunused-value]
/in/foo.cc:12:12: warning: unused variable 'max' [-Wunused-variable]
  int i,n=0,max;
            ^~~