Compilare: user.cpp: In function ‘int main()’: user.cpp:33:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < prime_fact.size(); ++i) { ^ user.cpp:40:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = n; j < v.size(); j += 2 * n) ^ user.cpp:45:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < v.size(); ++i) ^