Compilare: user.cpp: In function ‘int main()’: user.cpp:39:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0;j < a[i].size();j++) ~~^~~~~~~~~~~~~ user.cpp:21:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("entropy.in", "r", stdin); ^ user.cpp:22:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("entropy.out", "w", stdout); ^