二叉树层次遍历运行时出现如下错误，如何解决？（代码如下）

#include <iostream>
using namespace std;
typedef struct node {
    char data;
    struct node *lchild, *rchild;
}BTNode;//二叉树的类型定义
typedef struct {
    BTNode *data[200];
    int front, rear;
}SqQueue;//队的类型定义
void InitQueue(SqQueue *&q) {
    q = (SqQueue*)malloc(sizeof(SqQueue));
    q->front = q->rear = -1;
}
bool enQueue(SqQueue *&q, BTNode *b) {
    if (q->rear == 200 - 1)
        return false;
    q->rear = (q->rear + 1) % 200;
    q->data[q->rear] = b;
    return true;
}
bool deQueue(SqQueue *&q, BTNode *b) {
    if (q->front == q->rear)return false;
    q->front = (q->front + 1) % 200;
    b = q->data[q->front];
    return true;
}
bool QueueEmpty(SqQueue *q) { return (q->front == q->rear); }
void CreatBTNode(BTNode *&b, char *str) {
    BTNode *st[200], *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];
    }
}
void LevelOrder(BTNode *b, char *a) {
    BTNode *p;
    int i = 0;
    SqQueue *qu;
    InitQueue(qu);
    enQueue(qu, b);
    while (!QueueEmpty(qu)) {
        deQueue(qu, p);
        a[i] = p->data;i++;
        if (p->lchild != NULL)
            enQueue(qu, p->lchild);
        if (p->rchild != NULL)
            enQueue(qu, p->rchild);
    }
    a[i] = 0;
}
int main() {
    BTNode *M;
    char str[200] = "A(B(D(,G)),C(E,F))";
    CreatBTNode(M, str);//已经创建成功
    char a[200];
    LevelOrder(M, a);
    int len, i;
    len = strlen(a);
    for (i = len - 1;i >= 0;i--)
        cout << a[i]<<" ";
}

deQueue函数的b参数加个引用可以不崩溃，其他你再看看：

bool deQueue(SqQueue *&q, BTNode *&b) {
    if (q->front == q->rear)return false;
    q->front = (q->front + 1) % 200;
    b = q->data[q->front];
    return true;
}

把错误报告贴出来，好分析原因

deQueue函数中的p变量没有初始化
BTNode *p  = new BTNode;