Compilare: main.cpp: In function 'int main()': main.cpp:46:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0; j < mat[x].size(); ++j) ~~^~~~~~~~~~~~~~~ main.cpp:24:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("bfs.in", "r", stdin); ^ main.cpp:25:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("bfs.out", "w", stdout); ^ main.cpp:27:27: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &n, &m); ^ main.cpp:30:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &x, &y); ^