Compilare: user.cpp: In function ‘void flipColumns(std::vector<std::vector<int> >)’: user.cpp:12:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < matrix[0].size(); j ++) { ^ user.cpp:15:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < matrix.size(); i ++) { ^ user.cpp: In function ‘void flipLines(std::vector<std::vector<int> >, int, bool)’: user.cpp:34:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k == matrix.size()) { ^ user.cpp:39:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < matrix[0].size(); i ++) { ^ user.cpp: In function ‘int main()’: user.cpp:50:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("flip.in", "r", stdin); ^ user.cpp:51:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("flip.out", "w", stdout); ^ user.cpp:55:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &m); ^ user.cpp:61:39: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &matrix[i][j]); ^