双链表堆栈删除函数不起作用

我已经实现了双链表，以便在堆栈中推送和弹出值。我的弹出功能不起作用。我已经对这个程序进行了几次试运行，所有这些都是在纸上完成的。如有可能，请提供指导。

#include<iostream>
#include<conio.h>
#include<iomanip>
using namespace std;
struct node
{
node * prev;
int val;
node * next;    
};
class myStack
{
node * first;
node * cur;
node * prev0;
public:
myStack (): first(NULL), cur(NULL), prev0(NULL){}
void push();
void pop();
void noutput();
void output();
~myStack(){}
};
void myStack :: push()
{
cur = new node;
cur->prev = NULL;
cur->next = NULL;
cout<<"Enter the Number to push in Stack :"<<endl;
cin>>cur->val;
cout<<endl;
if(first == NULL)
{
first = prev0 = cur;
}
else
{
prev0->next = cur;
cur->prev = prev0;
prev0 = cur;
}
}
void myStack :: pop()
{       
prev0 = cur->prev;
delete cur;
prev0->next = NULL;
cur = prev0;
}
void myStack :: noutput()
{
cur = first;
system("cls");
cout<<setw(70)<<"NODE VIEW"<<endl;
cout<<setw(55)<<"Prev"<<"        Cur"<<"       Next";
cout<<endl<<endl;
while(cur)
{
cout<<setw(55)<<cur->prev<<" | "<<cur<<" | "<<cur->next<<endl;
cur = cur->next;
}
system("pause");
}
void myStack :: output()
{
cur = first;
system("cls");
cout<<setw(60)<<"STACK VIEW"<<endl<<endl;
while(cur)
{
cout<<setw(55)<<" | "<<cur->val<<endl;
cur = cur->next;
}
system("pause");
}
int main()
{
myStack q;
char op;
int key;
for(int i = 0; i < 1; )
{
system("cls");
cout<<"Press 1 to push value          :"<<endl;
cout<<"Press 2 to pop value           :"<<endl;
cout<<"Press 3 to Print Node View     :"<<endl;
cout<<"Press 4 to Print Stack View    :"<<endl;
cout<<"Press esc to exit              :"<<endl;
op = _getch();
key = op;
if(key == 49)
{
q.push();
}
else if(key == 50)
{
q.pop();
}
else if(key == 51)
{
q.noutput();
cout<<"nn";
}
else if(key == 52)
{
q.output();
cout<<"nn";
}
else if(key == 27)
i++;
else
{
cout<<"a Invalid Value Enter Again:"<<endl;
system("pause");
}   
}
system("pause");
return 0;
}