Compilare: user.cpp: In function ‘int bad(config)’: user.cpp:37:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] return c.size() >= 1 && c[0] == -1; ^ user.cpp: In function ‘void output(instance, config)’: user.cpp:68:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < c.size(); i++) ^