Compilare: user.cpp: In function ‘int main()’: user.cpp:31:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < C.size(); i++){ ^ user.cpp:32:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j = 0; j < C[i].size(); j++) ^ user.cpp:15:31: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ctc.in", "r", stdin); ^ user.cpp:16:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ctc.out", "w", stdout); ^ user.cpp:17:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &n, &m); ^ user.cpp:19:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &x, &y); ^