#include <iostream>
#include <cstddef>

class Stack
{
  struct Node
  {
    int data;
    Node* prev;
    Node* next;

    Node() = default;
    Node(int data_ = {}, Node* prev_ = nullptr, Node* next_ = nullptr)
      : data(data_), prev(prev_), next(next_) { }
  };
 public:
  Stack() {
    this->len = 0u;
    this->top_ = nullptr;
  }
  ~Stack() {
    this->clear();
  }

  void push(int item) {
    if (top_ == nullptr) {
      top_ = new Node(item);
    } else {
      top_->next = new Node(item, top_);
      top_ = top_->next;
    }
    ++len;
  }
  bool pop() {
    if (size() == 0) {
      return false;
    } else {
      auto new_top_ = top_->prev;
      delete top_;
      top_ = new_top_;
      --len;
      return true;
    }
  }
  void clear() {
    while (len != 0)
      this->pop();
  }
  ::size_t size() const {
    return this->len;
  }
  bool empty() const {
    return size() == 0;
  }
  int top() const {
    return this->top_->data;
  }

 private:
  ::size_t len;
  Node* top_;
};

int main()
{
  ::Stack stack;
  std::cout << "pushing order: ";
  for (int i = 0; i < 10; ++i) {
    std::cout << i << ' ';
    stack.push(i);
  }
  std::endl(std::cout);
  
  std::cout << "popping order: ";
  while (!stack.empty()) {
    std::cout << stack.top() << ' ';
    stack.pop();
  }
  std::endl(std::cout);

  std::cout << "Is the stack now empty? " << std::boolalpha
            << stack.empty() << std::endl;
}