二叉树添加索引

前序遍历创建，前序打印。。。中序遍历添加索引，再循环打印。。。

typedef struct BiNode
{
    char data;
    char ltag, rtag;
    struct BiNode *lchild, *rchild;
}BiNode;

void createTree(BiNode **root);
void printTree(BiNode *root, int lever);
void addThread(BiNode *root, BiNode **pre); 
void PTree(BiNode *root, const BiNode *pre);

int main(int argc, char *argv[])
{
    BiNode *root = NULL;
    BiNode pre = {0, 't', 't', NULL, NULL};
    BiNode *prePointer = ⪯ 
    int lever = 1;
    
    createTree(&root);
    printTree(root, lever);
    
    pre.ltag = 't';
    pre.lchild = root;
    
    addThread(root, &prePointer);
    
    pre.rtag = 't';
    pre.rchild = prePointer;
    prePointer->rtag = 't';
    prePointer->rchild = ⪯
    
    PTree(root, &pre);
    return 0;
}

void createTree(BiNode **root)
{
    char el;
    scanf("%c", &el);

    if(el == ' ')
    {
        *root = NULL;
    }else {
        *root = (BiNode *)malloc(sizeof(BiNode));
        (*root)->data = el;
        (*root)->ltag = 'l';
        (*root)->rtag = 'l';
        
        createTree(&((*root)->lchild));
        createTree(&((*root)->rchild));
    }
}

void printTree(BiNode *root, int lever)
{
    if(root)
    {
        printf("data: %c, lever: %d \n", root->data, lever);
        printTree(root->lchild, lever+1);
        printTree(root->rchild, lever+1);
    }
}

void addThread(BiNode *root, BiNode **pre)
{
    if(root)
    { 
        if(root->lchild)
        {
            addThread(root->lchild, pre);
        }else {
            root->ltag = 't';
            root->lchild = (*pre);
        }
        if((*pre)->rchild == NULL)
        {
            (*pre)->rtag = 't';
            (*pre)->rchild = root;
        }
        (*pre) = root;
        
        addThread(root->rchild, pre);
    }
}

void PTree(BiNode *root, const BiNode *pre)
{
    BiNode *p = root;
    while(p->rchild != pre)
    {
        while(p->ltag == 'l')
        {
            p = p->lchild;
        }
        printf("%c ", p->data);
        
        while(p->rtag == 't' && p->rchild != pre)
        {
            p = p->rchild;
            printf("%c ", p->data);
        }
        
        p = p->rchild;
    }
    printf("%c \n", p->data);
}

 创建的时候输入需要类似：AB  C  \n

B C后面各有两个空格，代表其左子树和右子树都为空。。。。