/in/foo.cc: In function 'BigInt operator*(const BigInt&, const BigInt&)':
/in/foo.cc:36:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |         for (int i = 0; i < a.digits.size(); ++i)
      |                         ~~^~~~~~~~~~~~~~~~~
/in/foo.cc:37:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   37 |             for (int j = 0; j < b.digits.size(); ++j)
      |                             ~~^~~~~~~~~~~~~~~~~
/in/foo.cc:40:38: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |         for (int i = 0, carry = 0; i < prod.size(); ++i)
      |                                    ~~^~~~~~~~~~~~~
/in/foo.cc: In member function 'std::string BigInt::toString() const':
/in/foo.cc:59:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   59 |         for (int i = 0; i < rev.size(); ++i)
      |                         ~~^~~~~~~~~~~~