先序中序转后序没输出 思路是不断地划分mid的长度

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define MaxArraySize 20

typedef struct BinTreeNode* BinTree;

struct BinTreeNode
{
char element;
BinTree leftchild;
BinTree rightchild;
};

BinTree CreateTree_Pre(char* preOrder, char* midOrder, int n)
{
BinTree tree = (BinTree)malloc(sizeof(struct BinTreeNode));
if (!tree)
return;
tree->element = preOrder[0];
tree->leftchild = NULL;
tree->rightchild = NULL;
if (n == 1) //只剩下一个结点时，直接返回
return tree;

int  midPtr, leftLength, rightLength;
midPtr = 0;
while (midOrder[++midPtr] != preOrder[0])    //找出中序遍历中根节点的位置
    ;
leftLength = midPtr;        //左子树结点数
rightLength = n - leftLength - 1;       //右子树结点数

//偷懒起见，未创建新的数组
tree->leftchild = CreateTree_Pre(&preOrder[1], midOrder, leftLength);     //注意左右子树在原数组中的位置
tree->rightchild = CreateTree_Pre(&preOrder[leftLength + 1], &midOrder[leftLength + 1], rightLength);
return tree;

}

void PrintPostOrder(BinTree t) //打印后序遍历结果
{
if (!t)
return;
PrintPostOrder(t->leftchild);
PrintPostOrder(t->rightchild);
printf("%c", t->element);
}

int main()
{
BinTree t = (BinTree)malloc(sizeof(struct BinTreeNode));
char pre[MaxArraySize], mid[MaxArraySize];
printf("请输入先序遍历结果：");
gets(pre);
printf("请输入中序遍历结果：");
gets(mid);
printf("后序遍历结果为：");
t = CreateTree_Pre(pre, mid, strlen(pre));
PrintPostOrder(t);

return 0;

}