Compilare: user.cpp: In function ‘int main()’: user.cpp:15:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=2;i<=N;++i) ^ user.cpp:24:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=1;j<=N;++j) ^ user.cpp:30:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(k<N) ^ user.cpp:41:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<=N;i+=10) ^