Compilare: user.cpp: In function ‘int main()’: user.cpp:2:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] int main(){freopen("sah.in","r",stdin);freopen("sah.out","w",stdout);int n;scanf("%d",&n);for(int i=0;i<n;++i){for(int j=0;j<n;++j){printf("%d ",((i>>1)<<1)^(j<(i>>1)?0:1));}printf("\n");}} ^ user.cpp:2:69: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] int main(){freopen("sah.in","r",stdin);freopen("sah.out","w",stdout);int n;scanf("%d",&n);for(int i=0;i<n;++i){for(int j=0;j<n;++j){printf("%d ",((i>>1)<<1)^(j<(i>>1)?0:1));}printf("\n");}} ^ user.cpp:2:90: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] int main(){freopen("sah.in","r",stdin);freopen("sah.out","w",stdout);int n;scanf("%d",&n);for(int i=0;i<n;++i){for(int j=0;j<n;++j){printf("%d ",((i>>1)<<1)^(j<(i>>1)?0:1));}printf("\n");}} ^