Compilare: user.cpp: In function ‘int main()’: user.cpp:24:35: 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:25:37: 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:17:23: warning: iteration 1000000u invokes undefined behavior [-Waggressive-loop-optimizations] res[i] += res[i - 1]; ^ user.cpp:13:20: note: containing loop for (int i = 1; i <= maxn; ++i) { ^