Compilare: user.cpp: In constructor ‘BIT::BIT(std::vector<int>)’: user.cpp:20:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<arr_.size(); i++) { ~^~~~~~~~~~~~ user.cpp: In member function ‘void BIT::update(int, int)’: user.cpp:27:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < arr.size()) { ~~^~~~~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:85:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("bit.in", "r", stdin); ^ user.cpp:86:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("bit.out", "w", stdout); ^