Compilare: user.cpp: In function ‘std::string process_line(std::string&)’: user.cpp:44: warning: comparison between signed and unsigned integer expressions user.cpp:68: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘bool eval_expression(std::string&, std::map<char, bool, std::less<char>, std::allocator<std::pair<const char, bool> > >&)’: user.cpp:81: warning: comparison between signed and unsigned integer expressions user.cpp:78: warning: unused variable ‘ret’ user.cpp: In function ‘int main()’: user.cpp:131: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result