foo.cc: In constructor 'Sig::Sig(std::vector<std::complex<double> >*)':
foo.cc:29:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         while (m < V->size()) {
                ~~^~~~~~~~~~~
foo.cc: In copy constructor 'Sig::Sig(const Sig&)':
foo.cc:38:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < s.V->size(); ++i) {
                         ~~^~~~~~~~~~~~~
foo.cc: In member function 'Sig Sig::fft() const':
foo.cc:61:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < V->size(); ++i) {
                         ~~^~~~~~~~~~~
foo.cc: In member function 'Sig Sig::ifft() const':
foo.cc:89:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < V->size(); ++i) {
                         ~~^~~~~~~~~~~
foo.cc: In copy constructor 'BigInteger::BigInteger(const BigInteger&)':
foo.cc:164:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < s.T->size(); ++i) {
                         ~~^~~~~~~~~~~~~
foo.cc: In member function 'BigInteger BigInteger::operator*(const BigInteger&)':
foo.cc:182:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < T->size(); ++i) {
                         ~~^~~~~~~~~~~
foo.cc:185:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < rhs.T->size(); ++i) {
                         ~~^~~~~~~~~~~~~~~
foo.cc:195:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < lhs_out.V->size(); ++i) {
                         ~~^~~~~~~~~~~~~~~~~~~
foo.cc:201:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < pro_out.V->size(); ++i) {
                         ~~^~~~~~~~~~~~~~~~~~~
foo.cc: In member function 'void BigInteger::rearrange()':
foo.cc:209:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < T->size() - 1; ++i) {
                         ~~^~~~~~~~~~~~~~~
foo.cc: In member function 'void BigInteger::print()':
foo.cc:225:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < T->size(); ++i) {
                         ~~^~~~~~~~~~~
foo.cc: In member function 'char* BigInteger::str()':
foo.cc:234:37: warning: format '%d' expects argument of type 'int', but argument 3 has type '__gnu_cxx::__alloc_traits<std::allocator<long long int> >::value_type {aka long long int}' [-Wformat=]
         sprintf(s, "%d", (*T)[l - 1]);
                                     ^
foo.cc:237:74: warning: format '%d' expects argument of type 'int', but argument 3 has type '__gnu_cxx::__alloc_traits<std::allocator<long long int> >::value_type {aka long long int}' [-Wformat=]
             sprintf(s + start + (i - 1) * n_base, "%05d", (*T)[l - i - 1]);
                                                                          ^
foo.cc: In function 'int main()':
foo.cc:273:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%s %s", a, b);
         ~~~~~^~~~~~~~~~~~~~~