Compilare: user.cpp: In function ‘ll closest_pair(int, int)’: user.cpp:42:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < useful.size(); ++i) { ^ user.cpp:43:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i + 1; j < useful.size() && j - i + 1 <= 8; ++j) { ^ user.cpp: In function ‘int main()’: user.cpp:51:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cmap.in", "r", stdin); ^ user.cpp:52:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cmap.out", "w", stdout); ^