Compilare: user.cpp: In function ‘void solve()’: user.cpp:33:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j = 0; j < l[i].size(); ++ j) ^ user.cpp:44:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(k = 0; k < v[j].size(); ++ k) ^ user.cpp: In function ‘void read()’: user.cpp:15:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("nrcuv.in ", "r", stdin); ^ user.cpp:16:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("nrcuv.out", "w", stdout); ^ user.cpp:17:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &n, &m); ^ user.cpp:20:33: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%c %c\n", &a, &b); ^