为什么p St b报错“表达式必须包含指向类的指针类型”？

#include<iostream>
#include<stdlib.h>
#define MaxSize 50

typedef int ElemType;
typedef struct Node *Position;
typedef Position BTNode;
struct Node
{
    ElemType data;
    struct node *lchild;
    struct node *rchild;
}b;

void CreateBTree(BTNode * &b, char*str)
{
    BTNode *St[MaxSize], *p;
    int top = -1, k, j = 0;
    char ch;
    b = NULL;
    ch = str[j];
    while (ch != '\0')
    {
        switch (ch)
        {
        case '(':top++; St[top] = p; k = 1; break;
        case')':top--; break;
        case',':k = 2; break;
        default:p = (BTNode *)malloc(sizeof(BTNode));
            p->data = ch;
            p->lchild = p->rchild = NULL;
            if (b == NULL)
                b = p;
            else
            {
                switch (k)
                {
                case 1:St[top]->lchild = p; break;
                case 2:St[top]->rchild = p; break;
                }
            }
        }
        j++;
        ch = str[j];
    }
}

其中p St b报错“表达式必须包含指向类的指针类型”
请问大佬们这是为什么呀？

typedef int ElemType;
typedef struct Node *Position;
typedef Position BTNode;
struct Node
{
ElemType data;
struct node *lchild;
struct node *rchild;
}b;
粗略看了一下上面的应该等价于下面的
typedef int ElemType;
typedef struct Node
{
ElemType data;
struct node *lchild;
struct node *rchild;
}*Position, *BTNode, Node;
Node b;
这个
所以BTNode * p; 相当于Node **p，所以你就知道了（Node *）不是一个类，而是一个指针类型，你非要这么写的话可以试试(*p）->
或者 BTNode p,建议“}*Position, *BTNode, Node;”改为“}*Position, BTNode, Node;”
另外建议指针数组啥的该加的括号加上