Compilare: user.cpp: In function ‘int main()’: user.cpp:26:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("difprim.in","r",stdin) ; ^ user.cpp:27:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("difprim.out","w",stdout) ; ^ user.cpp:28:25: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&a,&b) ; ^ user.cpp: In function ‘void sieve()’: user.cpp:14:19: warning: iteration 999998 invokes undefined behavior [-Waggressive-loop-optimizations] if (ciur[i] == 0){ ~~~~~~^ user.cpp:13:20: note: within this loop for (i = 2 ; i <= NMAX ; ++ i){ ^