关于非递归创建二叉树

关于非递归创建二叉树在网上也看到了各种各样的算法，但是不知道为什么，每个算法我几乎是照搬到vs都没办法正常运行，每次都提示指针为空导致无法运行，所以想请教一下，究竟哪边有问题？
下附代码：

#include<stdio.h>
#include<stdlib.h>
typedef struct node
{
    char data;
    struct node* lchild, * rchild;
}tree;
void inorder(tree* t)
{
    tree* s[100];
    int top = 0;    
    tree* p = t;
    while (p != NULL || top != 0)
    {
        while (t)
        {
            s[++top] = p; p = p->lchild;
        }
        if (top)
        {
            p = s[top--];
            if (p->data != ' ')
                printf("%c ", p->data);
            p = p->rchild;
        }
    }
}
void create_tree(tree* t,char*str)
{
    tree* s[100];
    tree* p = NULL;
    int top, k, j; char ch;
    top = 0; j = 0; k = 0;
    t = NULL;
    ch = str[j];
    while (ch != '\0')
    {
        switch (ch)
        {
        case'(':top++; s[top] = p; k = 1; break;
        case')':top--; break;
        case',':k = 2; break;
        default:
            p = (tree*)malloc(sizeof(tree));
            p->data = ch; p->lchild = p->rchild = NULL;
            printf("%c", p->data);
            if (t == NULL)
                t = p;
            else
            {
                switch(k)
                {
                case 1:s[top]->lchild = p; break;
                case 2:s[top]->rchild = p; break;
                }
            }
        }
        ch = str[++j];
    }
}

void main()
{
    tree* t;
    t = (tree*)malloc(sizeof(tree));
    char str[100];
    printf("请创建二叉树：\n");
    scanf("%s", &str);
    create_tree(t,str);
    printf("%c", t->data);
    printf("\n二叉树的中序遍历输出为：");
    inorder(t);
    
}

case的括号是啥