c++中用new实现c中realloc出错

// 0415.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
using namespace std;
#include <stdlib.h>

const int nlen = 4;   //分配初始内存大小
const int nadd = 2;   //内存不足，增加内存

struct stack
{
    int *pa;
    int *pb;
    int nsize;
};

void create(stack &s);
void push(stack &s,int e);   //插入元素
void pop(stack &s, int &e);  //删除元素
bool empty(stack &s);        //判断栈是否为空
void destory(stack &s);       //销毁栈

int main(int argc, char* argv[])
{
    while(1)
    {
        stack sql;
        create (sql);
        
        cout<<"please input a number:"<<endl;
        
        int nt;
        int e ;
        cin>>nt;

        if(0 == nt)    //当输入0时，退出循环
        {
            return 0;
        }
        
        while(nt)
        {
            push(sql, nt%8);   //10进制数除以8，余数进栈
            nt = nt/8;
        }
        
        while(!empty(sql))    //余数出栈
        {
            pop(sql, e);
            cout<<e;
        }         
        cout<<endl;
        free(sql.pa);
        //system("cls");
        
        //delete [] sql.pa;
    }
    return 0;   
}

void create(stack &s)
{
    //s.pa = new int[nlen];
    s.pa = (int *)malloc(nlen * sizeof(int));
    if(!s.pa)
    {
        return ;
    }
    s.pb = s.pa;
    s.nsize = nlen;
}

void push(stack &s, int e)
{
    if(s.pb - s.pa >= s.nsize)
    {
        //delete [] s.pa;
        //s.pa = NULL;
        //s.pa = new int[(s.nsize + nadd)];
        s.pa = (int *)realloc(s.pa,(s.nsize + nadd) * sizeof(int));
        
        if(!s.pa)
        {
            cout<<"memory error!"<<endl;
        }
        s.pb = s.pa + s.nsize;   
        s.nsize += nadd;   
    }
    *(s.pb++) = e;
}

void pop(stack &s, int &e)
{
    if(s.pa == s.pb)
    {
        cout<<"error"<<endl;
    }
    e = *(--s.pb);
}

bool empty(stack &s)
{
    if(s.pa == s.pb)
    {
        return true;
    }
    else
        return false;
}

void destory(stack &s)
{

}