C++非递归建立二叉树实例

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;}