/in/foo.cc: In function 'void strtobig(std::__cxx11::string, bignum&)':
/in/foo.cc:9:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s.length();i++){
              ~^~~~~~~~~~~
/in/foo.cc: In function 'void Mul2(bignum, bignum, bignum&)':
/in/foo.cc:21:10: warning: unused variable 'len' [-Wunused-variable]
  int i,j,len=0;
          ^~~