Compilare: user.cpp: In function ‘std::vector<double> operator+(std::vector<double>, std::vector<double>)’: user.cpp:6:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i) ^ user.cpp: In function ‘std::vector<double> operator*(std::vector<double>, double)’: user.cpp:11:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i) ^ user.cpp: In function ‘int main()’: user.cpp:54:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("gauss.in", "r", stdin); ^ user.cpp:55:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("gauss.out", "w", stdout); ^