/in/foo.cc: In function 'int main()':
/in/foo.cc:14:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0; i<s1.length(); i++)
                      ~^~~~~~~~~~~~
/in/foo.cc:34:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0; i<s1.length(); i++)
                      ~^~~~~~~~~~~~
/in/foo.cc:32:9: warning: 'flag' may be used uninitialized in this function [-Wmaybe-uninitialized]
         if(!flag)
         ^~