Compilare: user.cpp: In function ‘int main()’: user.cpp:8:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i <= n; ++i) ^ user.cpp:10:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 2; i <= n; ++i) ^ user.cpp:11:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 2 * i; j <= n; j += i) ^ user.cpp:13:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i <= n; ++i) ^ user.cpp:4:11: warning: unused variable ‘i’ [-Wunused-variable] unsigned i,n, x = 0, phi[100]; ^