Compilare: user.cpp: In function ‘long long int form(std::vector<int>&, int)’: user.cpp:19:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < a.size(); ++i) { ^ user.cpp: In function ‘int main()’: user.cpp:98:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("gap.in", "r", stdin); ^ user.cpp:99:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("gap.out", "w", stdout); ^