Compilare: user.cpp: In function ‘std::istream& operator>>(std::istream&, gf&)’: user.cpp:85:1: warning: no return statement in function returning non-void [-Wreturn-type] } ^ user.cpp: In function ‘std::ostream& operator<<(std::ostream&, const gf&)’: user.cpp:91:1: warning: no return statement in function returning non-void [-Wreturn-type] } ^ user.cpp: In function ‘std::ostream& operator<<(std::ostream&, const arbore_kruskal&)’: user.cpp:113:1: warning: no return statement in function returning non-void [-Wreturn-type] } ^