Compilare: user.cpp: In function ‘int main()’: user.cpp:78:61: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int t = 0; t < A[i][j].size(); t ++){ ^ user.cpp:19:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("android.in" ,"r", stdin ); ^ user.cpp:20:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("android.out","w", stdout); ^ user.cpp:22:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &N, &M); ^