/in/foo.cc: In function 'int main()':
/in/foo.cc:19:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i < a.length(); i++)
                 ~~^~~~~~~~~~~~
/in/foo.cc:41:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<=c.length();i++)
                 ~^~~~~~~~~~~~