Compilare: user.cpp: In function ‘int main()’: user.cpp:12:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1;i<=n;i++) ^ user.cpp:14:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=2;i<=n;i++) ^ user.cpp:16:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=2*i;j<=n;j=j+i) ^