关于二叉树的生成, 遍历 在线求指导!该如何处理

#include <iostream>
using namespace std;

const int queueSize = 100; //层序遍历所用的队列的最大度

struct biNode //用结构体定义二叉树
{
    char word;
    biNode *lchild, *rchild; 
};

biNode *creat(biNode *node) //生成二叉树
{
    cout<<"请输入节点\n (输入数字 0 , 即结束节点输入\n";
    char word;             
    cin>>word;
    if (word == '0')
        return NULL;   //结束子树
    else
    {
        node = new biNode; 
        node->word = word;
        node->lchild = creat(node);
        node->rchild = creat(node);
    }

}

biNode *setup(biNode *root) 
{
    biNode *go; //执行节点
    go = new biNode;
    cout<<"请输入根节点\n ";
    cin>>go->word;
    root = go;
    creat(go);  //递归生成二叉树
    return root;
}

void preOrder(biNode *root) //前序遍历
{
    if (root != NULL)
    {
        cout<<root->word<<" ";
        preOrder(root->lchild); 
        preOrder(root->rchild);
    }
}

void inOrder(biNode *root) //中序遍历
{
    if (root != NULL)
    {
        inOrder(root->lchild);
        cout<<root->word<<" ";
        inOrder(root->rchild);
    }
}

void postOrder(biNode *root) //后续遍历
{
    if (root != NULL)
    {
        postOrder(root->lchild);
        postOrder(root->rchild);
        cout<<root->word<<" ";
    }
}

void levelOrder(biNode *root) //层序遍历
{
    biNode *queue[queueSize];
    biNode *q;
    int front, rear;
    front = rear = -1;
    if (root == NULL)
        return ;
    queue[++rear] = root;
    while (front != rear)
    {
        q = queue[++front];
        cout<<q->word;
        if (q->lchild != NULL) 
            queue[++rear] = q->lchild;
        if (q->rchild != NULL)
            queue[++rear] = q->rchild;
    }
}
        
int main()
{
    
    biNode *root, *go;
    root = go = NULL; //初始化
    while(1)
    {
        cout<<"\t\t二叉树, 二叉树, 二叉树!\n\n";
        cout<<"1, 生成二叉树\n";
        cout<<"2, 前序遍历\n";
        cout<<"3, 中序遍历\n";
        cout<<"4, 后续遍历\n";
        cout<<"5, 程序遍历\n";
        cout<<"6, 退出\n";
        cout<<"输入 1 到 6 的数字, 选择相应功能\n";
        int judge;
        cin>>judge;
        switch (judge)
        {
        case 1:
            {
                root = setup(go);
                break;
            }
        case 2:
            {
                cout<<"前序遍历:\n";
                preOrder(root);
                break;
            }
        case 3:
            {
                cout<<"中序遍历:\n";
                inOrder(root);
                break;
            }
        case 4:
            {
                cout<<"后续遍历:\n";
                postOrder(root);
                break;
            }
        case 5:
            {
                cout<<"层序遍历:\n";
                levelOrder(root);
                break;
            }
        case 6:
            {
                exit(1);
            }
        default:
            {
                cout<<"Please enter a number from 1 to 6!\n";
                break;
            }
        }
    }
    return 0;
}

        
node->lchild = creat(node);
node->rchild = creat(node);