Compilare: main.cpp: In function 'void go(int, Divisor)': main.cpp:18:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (step == primes.size ()) { ~~~~~^~~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:45:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("media.in", "r", stdin); ^ main.cpp:46:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("media.out", "w", stdout); ^