Compilare: user.cpp: In function ‘int main()’: user.cpp:26:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sumdiv2.in","r",stdin); ^ user.cpp:27:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sumdiv2.out","w",stdout); ^ user.cpp: In function ‘void pre()’: user.cpp:19:21: warning: iteration 999999u invokes undefined behavior [-Waggressive-loop-optimizations] res[i] += res[i-1]; ^ user.cpp:15:15: note: containing loop for(int i=1;i<=maxn;++i) { ^