Compilare: user.cpp: In function ‘int main()’: user.cpp:15:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i <= N; i ++) ^ user.cpp:20:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 2; i <= N; i ++) ^ user.cpp:22:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(F[i] == i) ^ user.cpp:23:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = i; j <= N; j += i) ^