/in/foo.cc: In member function 'BigInteger BigInteger::operator*(BigInteger::LL)':
/in/foo.cc:52:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<s.size(); i++)c.s.push_back(s[i]*b);
                ~^~~~~~~~~
/in/foo.cc:53:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<c.s.size()-1; i++) {
                ~^~~~~~~~~~~~~
/in/foo.cc: In function 'std::ostream& operator<<(std::ostream&, const BigInteger&)':
/in/foo.cc:72:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0; j<strlen(buf); j++)output<<buf[j];
                 ~^~~~~~~~~~~~