Compilare: main.cpp: In function 'int main()': main.cpp:336:21: warning: passing NULL to non-pointer argument 1 of 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]' [-Wconversion-null] 336 | else g<<NULL<<'\n'; | ^~~~ In file included from /usr/include/c++/10/iostream:39, from main.cpp:1: /usr/include/c++/10/ostream:166:23: note: declared here 166 | operator<<(long __n) | ~~~~~^~~ main.cpp:341:21: warning: passing NULL to non-pointer argument 1 of 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]' [-Wconversion-null] 341 | else g<<NULL<<'\n'; | ^~~~ In file included from /usr/include/c++/10/iostream:39, from main.cpp:1: /usr/include/c++/10/ostream:166:23: note: declared here 166 | operator<<(long __n) | ~~~~~^~~ main.cpp:345:17: warning: unused variable 'nr' [-Wunused-variable] 345 | int nr = -1; | ^~ main.cpp: In function 'nod* treesplay(nod*, int)': main.cpp:108:1: warning: control reaches end of non-void function [-Wreturn-type] 108 | } | ^