Compilare: user.cpp: In function ‘const BigInteger operator*(const BigInteger&, const BigInteger&)’: user.cpp:106:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0, j, t; i < lhs.d.size(); ++i) { ^ user.cpp:107:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0, t = 0; j < rhs.d.size() || t; ++j, t /= 10) { ^ user.cpp:109:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j < rhs.d.size()) t += lhs.d[i] * rhs.d[j]; ^