Compilare: user.cpp: In function ‘int main()’: user.cpp:130:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = ans->begin (); k < ans->size (); ++i, ++k) ^ user.cpp:120:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("expr.in", "r", stdin); ^ user.cpp:121:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("expr.out", "w", stdout); ^ user.cpp:122:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%s", S); ^