利用栈实现二叉树的先序，中序，后序遍历的非递归操作

 #include
 #include
 #include
 #include
 #include
 #include
 using namespace std;
 typedef struct BiTNode{
     char data;
     BiTNode *lchild, *rchild;
 }BiTNode,*BiTree;

 void CreateBiTree(BiTree &T)//建树，按先序顺序输入节点
 {
     char ch;
     scanf("%c",&ch);
     if(ch==' ')
     {
         T=NULL;
         return;
     }
     else
     {
         T=(BiTree)malloc(sizeof(BiTNode));
         if(!T)
             exit(1);
         T->data=ch;
         CreateBiTree(T->lchild);
         CreateBiTree(T->rchild);
     }
 }
 void InOrderTraverse(BiTree T)//非递归中序遍历
 {

     stack Stack;
     if(!T)
     {
         printf("空树！\n");
         return;
     }

     while(T || !Stack.empty())
     {
         while(T)
         {
             Stack.push(T);
             T=T->lchild;
         }
         T=Stack.top();
         Stack.pop();
         printf("%c",T->data);
         T=T->rchild;
     }
 }



 void PreOrderTraverse(BiTree T)//非递归先序遍历
 {

     stack Stack;
     if(!T)
     {
         printf("空树！\n");
         return;
     }
     while(T || !Stack.empty())
     {
         while(T)
         {
             Stack.push(T);
             printf("%c",T->data);
             T=T->lchild;
         }
         T=Stack.top();
         Stack.pop();
              T=T->rchild;
     }
 }


 void PostOrderTraverse(BiTree T)//非递归后序遍历,用一个标记标记右子树是否访问过
 {
     int flag[20];
     stack Stack;
     if(!T)
     {
         printf("空树！\n");
         return;
     }
     while(T)
     {
         Stack.push(T);
         flag[Stack.size()]=0;
         T=T->lchild;
     }
     while(!Stack.empty())
     {
         T=Stack.top();
         while(T->rchild && flag[Stack.size()]==0)
         {
             flag[Stack.size()]=1;
             T=T->rchild;
             while(T)
             {
                 Stack.push(T);
                 flag[Stack.size()]=0;
                 T=T->lchild;
             }
         }
         T=Stack.top();
         printf("%c",T->data);
         Stack.pop();
     }
 }
 void main()
 {

     BiTree T;
     CreateBiTree(T);
     PreOrderTraverse(T);
     printf("\n");
          InOrderTraverse(T);
     printf("\n");
     PostOrderTraverse(T);
     printf("\n");
 }