Compilare: user.cpp: In function ‘void sieve()’: user.cpp:56:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < primes.size() && primes[j] <= low[i] && primes[j] * i <= VALMAX; ++ j) ^ user.cpp: In constructor ‘InputReader::InputReader(const char*)’: user.cpp:16:43: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buffer, SIZE, 1, input_file); ^ user.cpp: In member function ‘void InputReader::advance()’: user.cpp:38:47: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buffer, SIZE, 1, input_file); ^