后缀表达式转为中缀表达式

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
using namespace std;

struct Node{
    int x;
    struct Node *Left,*Right;
};
typedef struct Node* Tree;

struct N{
    Tree x;
    struct N* next;
};
typedef struct N* Stack;

Stack CreateStack()
{
    Stack S=(Stack)malloc(sizeof(struct N));
    S->next=NULL;
    return S;
}

void Push(Tree x,Stack S)
{
    Stack tp=(Stack)malloc(sizeof(struct N));
    tp->x=x;
    tp->next=S->next;
    S->next=tp;
}

void Pop(Stack S)
{
    Stack tp=S->next;
    S->next=tp->next;
    free(tp);
}

void PostOrder(Tree t)
{
    if(t!=NULL)
    {
        PostOrder(t->Left);
        PostOrder(t->Right);
        printf("%c",t->x);
    }
}

void InOrder(Tree t)
{
    if(t!=NULL)
    {
        if(t->Left!=NULL) printf("(");
        InOrder(t->Left);
        printf("%c",t->x);
        InOrder(t->Right);
        if(t->Right!=NULL) printf(")");
    }
}
Tree Top(Stack S)
{
    return S->next->x;
}

int main(void)
{
    int len,n,i,x;
    Tree tp,p,h,t1,t2;
    Stack S=CreateStack();
    char str[120];
    gets(str);
    //printf("%s",str);
    len=strlen(str);
    for(i=0;i<len;i++)
    {
        Tree t=(Tree)malloc(sizeof(struct Node));
        if(t==NULL) printf("Out of Space!!!\n");
        t->x=str[i];
        if(str[i]>=‘a‘&&str[i]<=‘z‘) 
        {
            t->Left=NULL;
            t->Right=NULL;
            Push(t,S);
        }
        else
        {
            t1=Top(S);
            Pop(S);
            t2=Top(S);
            Pop(S);
            t->Left=t2;
            t->Right=t1;
            Push(t,S);
        }
    }
    tp=Top(S);
    Pop(S);
    InOrder(tp);
    //PostOrder(tp);
    return 0;
}

//ab+cde+**