Compilare: user.cpp: In function ‘int main()’: user.cpp:97:6: warning: unused variable ‘i’ [-Wunused-variable] int i; ^ user.cpp:89:51: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen((file_input + ".in").c_str(), "r", stdin); ^ user.cpp:90:53: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen((file_input + ".out").c_str(), "w", stdout); ^