#include<iostream>
#include<stdlib.h>
#include<assert.h>
using namespace std;
class SeqStack;
ostream &operator<<(ostream &os,SeqStack &s);

const int maxSize=50;
const int stackIncreament=20;
class SeqStack
{
public:
    SeqStack(int sz=50);
    ~SeqStack(){delete[] elements;}
    void Push(const int &x);
    bool IsFull()const{return (top==-1)?true:false;}
    friend ostream &operator<<(ostream &os,SeqStack &s);
private:
    int *elements;
    int top;
    int maxSize;
    void overflowProcess();
};

//构造函数
SeqStack::SeqStack(int sz):top(-1),maxSize(sz)
{
    elements=new int[maxSize];
    assert(elements!=NULL);
}

//新元素x进栈
void SeqStack::Push(const int &x)
{
    if(IsFull()==true)
        overflowProcess();
    elements[++top]=x;
}

//扩充栈的存储空间
void SeqStack::overflowProcess()
{
    int *newArray=new int[maxSize+stackIncreament];
    if(newArray==NULL){cerr<<"存储分配失败!"<<endl;exit(1);}
    for(int i=0;i<top;i++)
        newArray[i]=elements[i];
    maxSize=maxSize+stackIncreament;
    delete []elements;
}

//输出栈中元素的操作
ostream& operator<<(ostream& os,SeqStack& s)
{
    os<<"top="<<s.top<<endl;
    for(int i=0;i<=s.top;i++)
        os<<i<<":"<<s.elements[i]<<endl;
    return os;

}

int main()
{
    int n;
    cout<<"请输入栈的元素(以0结束):";
    cin>>n;
    SeqStack test;
    while(n!=-111)
    {
        test.Push(n);
        cin>>n;
    }
    cout<<test;
    return 0;
}

所以，应该怎么改呢？为什么会访问不了呢？