Compilare: user.cpp: In function ‘std::vector<int, std::allocator<int> > prefix(const std::string&)’: user.cpp:19: warning: comparison between signed and unsigned integer expressions user.cpp:31: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int main()’: user.cpp:48: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:49: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result