Compilare: main.cpp: In function 'int main()': main.cpp:63:33: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("inel.in","r",stdin); ^ main.cpp:64:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("inel.out","w",stdout); ^ main.cpp:66:19: 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 eratostene()': main.cpp:15:19: warning: iteration 18 invokes undefined behavior [-Waggressive-loop-optimizations] if(!ciur[i]){ ~~~~~~^ main.cpp:14:14: note: within this loop for(i=2;i<=20;i++) ~^~~~