C language binary tree non recursive traversal case analysis

In this paper, an example of C language implementation of binary tree non - recursive traversal method. It is a common technique in data structure and algorithm design. Share with you for your reference. Specific methods are as follows:

First order traversal:

void preOrder(Node *p) //non-recursive
{
  if(!p) return;
  stack<Node*> s;
  Node *t;
  s.push(p);
  while(!s.empty())
  {
    t=s.top();
    printf("%dn",t->data);
    s.pop();
    if(t->right) s.push(t->right);
    if(t->left) s.push(t->left);
  }
}

Middle order traversal:

void inOrder(Node *p)
{
if(!p)
return;
stack< pair<Node*,int> > s;
Node *t;
int unUsed;
s.push(make_pair(p,1));
while(!s.empty())
{
t=s.top().first;
unUsed = s.top().second;
s.pop();
if(unUsed)
{
if(t->right)
s.push( make_pair(t->right,1) );
s.push( make_pair(t,0) );
if(t->left)
s.push( make_pair(t->left,1));
}
else printf("%dn",t->data);
}
}

Sequential traversal:

void postOrder(Node *p)
{
  if(!p) return;
  stack<pair<Node*,int> > s;
  Node *t;
  int unUsed;
  s.push(make_pair(p,1));
  while(!s.empty())
  {
    t=s.top().first;
    unUsed=s.top().second;
    s.pop();
    if(unUsed)
    {
      s.push(make_pair(t,0);
      if(t->right)
        s.push(make_pair(t->right,1));
      if(t->left)
        s.push(make_pair(t->left,1));
    }
    else printf("%dn",t->data);
  }
}

I hope that this paper is helpful to the learning of C programming algorithm design.