/in/foo.cc: In function 'int check1(std::__cxx11::string, char)':
/in/foo.cc:11:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<s.length();++i)
                 ~^~~~~~~~~~~
/in/foo.cc: In function 'bool check(int, int, int)':
/in/foo.cc:21:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(t=1;t<W[i].length();++t)
             ~^~~~~~~~~~~~~~