Compilare: main.cpp: In function 'int main()': main.cpp:3:94: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] const int NMAX = 2 * 1e6 - 2;std::bitset<NMAX> ciur;int main(){freopen("ciur.in", "r", stdin);freopen("ciur.out", "w", stdout);int n;scanf("%d",&n);for(int i = 2; i * i <= n; ++i)if(!ciur[i-2])for(int j=i;i*j<=n;++j)ciur[i*j-2]=true;int cnt=0;for(int i=2;i<=n;++i)if(!ciur[i-2])++cnt;printf("%d\n",cnt);fclose(stdin);fclose(stdout);} ^ main.cpp:3:127: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] const int NMAX = 2 * 1e6 - 2;std::bitset<NMAX> ciur;int main(){freopen("ciur.in", "r", stdin);freopen("ciur.out", "w", stdout);int n;scanf("%d",&n);for(int i = 2; i * i <= n; ++i)if(!ciur[i-2])for(int j=i;i*j<=n;++j)ciur[i*j-2]=true;int cnt=0;for(int i=2;i<=n;++i)if(!ciur[i-2])++cnt;printf("%d\n",cnt);fclose(stdin);fclose(stdout);} ^ main.cpp:3:148: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] const int NMAX = 2 * 1e6 - 2;std::bitset<NMAX> ciur;int main(){freopen("ciur.in", "r", stdin);freopen("ciur.out", "w", stdout);int n;scanf("%d",&n);for(int i = 2; i * i <= n; ++i)if(!ciur[i-2])for(int j=i;i*j<=n;++j)ciur[i*j-2]=true;int cnt=0;for(int i=2;i<=n;++i)if(!ciur[i-2])++cnt;printf("%d\n",cnt);fclose(stdin);fclose(stdout);} ^