PBTree create()
{
 char ch[20];
 scanf("%s",ch);
 int len = strlen(ch);
 PBTree stack[20];
 /* 用来存储结点地址的栈 */ 
 int top = 0;
 /* 栈顶指针 */
 int flag = 1;
 /* 1表示现在需要创建左孩子，
 2表示需要创建右孩子，
 3表示左右孩子都已经创建完成 */
 int i = 0;
 PBTree temp;
 PBTree root = (PBTree)malloc(sizeof(BTree));
 root->data = ch[i++];
 root->lchild = NULL;
 root->rchild = NULL;
 stack[top ++] = root;
 while(i < len)
 {
  PBTree pNew = NULL;
  if(1 == flag) /* 创建左孩子 */
  {
   if('#' == ch[i])
    flag = 2;
   else
   {
    pNew = (PBTree)malloc(sizeof(BTree));
    pNew->lchild = NULL;
    pNew->rchild = NULL;
    pNew->data = ch[i];
    temp = stack[top - 1];
    temp->lchild = pNew;
    stack[top++] = pNew;
    flag = 1;
   }
  }
  else if(2 == flag)
  /* 创建右孩子 */
  {
   if('#' == ch[i])
    flag = 3;
   else
   {
    pNew = (PBTree)malloc(sizeof(BTree));
    pNew->lchild = NULL;
    pNew->rchild = NULL;
    pNew->data = ch[i];
    temp = stack[top - 1];
    temp->rchild = pNew;
    stack[top++] = pNew;
    flag = 1;
   }
  }
  else
  /* 左右孩子已经创建完成，需要出栈*/
  {
   temp = stack[--top];
   while(top > 1 && stack[top - 1]->rchild == temp)
    --top;
   flag = 2;
   --i;
  }
  ++i;
 }
 return root;
}