二叉树的递归先序中序后序

#include <stdio.h>
#include <malloc.h>
#define MaxSize 100
#define MaxWidth 40
typedef char ElemType;
typedef struct tnode
{
 ElemType data;
 struct tnode *lchild,*rchild;
} BTNode;
void CreateBTree(BTNode * &bt,char *str) /*由str创建二叉链bt*/
{
 BTNode *St[MaxSize],*p=NULL;
 int top=-1,k,j=0;  
 char ch;
 bt=NULL;   /*建立的二叉树初始时为空*/
 ch=str[j];
 while (ch!='\0')   /*str未扫描完时循环*/
 {
        switch(ch) 
  {
  case '(':top++;St[top]=p;k=1; break; /*为左孩子结点*/
  case ')':top--;break;
  case ',':k=2; break;                    /*为孩子结点右结点*/
  default:p=(BTNode *)malloc(sizeof(BTNode));
    p->data=ch;p->lchild=p->rchild=NULL;
    if (bt==NULL)                   /**p为二叉树的根结点*/
     bt=p;
    else         /*已建立二叉树根结点*/
    { switch(k)