/in/foo.cc: In member function 'big_integer big_integer::operator+(const big_integer&) const':
/in/foo.cc:87:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0, carry = 0; carry != 0 || i < v.size() || i < addend.v.size(); i++)
                                                  ~~^~~~~~~~~~
/in/foo.cc:87:68: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0, carry = 0; carry != 0 || i < v.size() || i < addend.v.size(); i++)
                                                                  ~~^~~~~~~~~~~~~~~~~
/in/foo.cc:90:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (i < v.size()) cur += v[i];
                 ~~^~~~~~~~~~
/in/foo.cc:91:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (i < addend.v.size()) cur += addend.v[i];
                 ~~^~~~~~~~~~~~~~~~~
/in/foo.cc: In member function 'big_integer big_integer::operator-(const big_integer&) const':
/in/foo.cc:114:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0, carry = 0; carry != 0 || i < v.size(); i++)
                                                  ~~^~~~~~~~~~
/in/foo.cc:117:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (i < subtrahend.v.size()) cur -= subtrahend.v[i];
                 ~~^~~~~~~~~~~~~~~~~~~~~
/in/foo.cc: In member function 'big_integer big_integer::operator*(const big_integer&) const':
/in/foo.cc:151:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < v.size(); i++)
                         ~~^~~~~~~~~~
/in/foo.cc:153:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j = 0; j < multiplier.v.size(); j++)
                             ~~^~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:155:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
                 if (i + j >= product.v.size()) product.v.resize(i + j + 1, 0);
                     ~~~~~~^~~~~~~~~~~~~~~~~~~
/in/foo.cc:159:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
                     if (i + j + 1 >= product.v.size()) product.v.resize(i + j + 1 + 1, 0);
                         ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~