Compilare: user.cpp: In function ‘void custi(std::vector<std::vector<int> >, std::vector<int>&)’: user.cpp:20:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int size = 0; size < M.size() - 1; ++size) { ^ user.cpp:21:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < M.size(); ++i) { ^ user.cpp:22:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 1; j < M.size(); ++j) { ^ user.cpp:23:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ((i + size) < M.size() && (j + size) < M.size()) { ^ user.cpp:23:57: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ((i + size) < M.size() && (j + size) < M.size()) { ^ user.cpp: In function ‘int main()’: user.cpp:35:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("custi.in", "r", stdin); ^ user.cpp:36:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("custi.out", "w", stdout); ^