Compilare: user.cpp: In function ‘int main()’: user.cpp:44:35: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘std::tr1::_Hashtable<std::basic_string<char>, std::basic_string<char>, std::allocator<std::basic_string<char> >, std::_Identity<std::basic_string<char> >, std::equal_to<std::basic_string<char> >, std::tr1::hash<std::basic_string<char> >, std::tr1::__detail::_Mod_range_hashing, std::tr1::__detail::_Default_ranged_hash, std::tr1::__detail::_Prime_rehash_policy, false, true, true>::size_type {aka unsigned int}’ [-Wformat=] printf("%lu\n", trees.count(str)); ^