Compilare: main.cpp: In function 'int main()': main.cpp:24:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("prim.in","r",stdin) ; ^ main.cpp:25:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("prim.out","w",stdout) ; ^ main.cpp:27:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n) ; ^ main.cpp: In function 'void sieve()': main.cpp:13:19: warning: iteration 1399999 invokes undefined behavior [-Waggressive-loop-optimizations] if (ciur[i] == 0){ ~~~~~~^ main.cpp:12:20: note: within this loop for (i = 2 ; i <= NMAX ; ++ i){ ^