Compilare: user.cpp: In function ‘int main()’: user.cpp:16:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("exp.in","r",stdin); ^ user.cpp:17:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("exp.out","w",stdout); ^ user.cpp:43:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&m,&N); ^ user.cpp:46:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&x); ^ user.cpp:32:11: warning: iteration 29999u invokes undefined behavior [-Waggressive-loop-optimizations] if(a[j]==0) ^ user.cpp:30:1: note: containing loop for(j=2;j<=N;++j) ^ user.cpp:24:9: warning: iteration 14999u invokes undefined behavior [-Waggressive-loop-optimizations] a[j]=1; ^ user.cpp:23:1: note: containing loop for(j=2*2;j<=N;j=j+2) ^