Iterative inorder traversal of a Binary Tree in C++11

iterative_inorder_traversal.cpp

#include <iostream>
#include <stack>
#include <algorithm>

using namespace std;

struct node {
  int value;
  node* left;
  node* right;

  node(int value, node* left, node* right) {
    this->value = value;
    this->left = left;
    this->right = right;
  }

  ~node() {
    delete this->left;
    delete this->right;
  }
};

node* bin(int v, node* left, node* right) {
  return new node(v, left, right);
}

node* leaf(int v) {
  return bin(v, NULL, NULL);
}

void visit(node* n) {
  cout << n->value << endl;
}

void inorder(node* n) {
  stack<pair<node*, bool> > s;
  auto defer = [&](node* n) { s.push(make_pair(n, true)); };
  auto call = [&](node* n) { s.push(make_pair(n, false)); };

  call(n);

  while (!s.empty()) {
    n = s.top().first;
    bool defered = s.top().second;
    s.pop();
    if (n == NULL)
      continue;
    if (!defered) {
      defer(n);
      call(n->left);
    } else {
      visit(n);
      call(n->right);
    }
  }
}

int main() {
  node* a = bin(3, bin(1, NULL, leaf(2)), bin(5, leaf(4), leaf(6)));
  inorder(a);
  delete a;
  return 0;
}