Compilare: user.cpp: In function ‘int main()’: user.cpp:23:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j = 0;j < v[i].size(); ++j) { ^ user.cpp:12:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("heavymetal.in","r",stdin); ^ user.cpp:13:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("heavymetal.out","w",stdout); ^ user.cpp:14:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:16:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &a, &b); ^