Thnx for The Tip, But Im Still stuck

hehehe
#include<iostream.h>
#include<conio.h>
#include<process.h>
#include<malloc.h>
// Creating a NODE Structure
struct node
{
int data;
struct node *next;
};
// Creating a class STACK
class stack
{
struct node *top;
public:
stack() // constructure
{
top=NULL;
}
void push(); // to insert an element
void pop(); // to delete an element
void show(); // to show the stack
void balance(); //balance the parenthesis
bool isEmpty(const stack& s);
};
// PUSH Operation
void stack::push()
{
int value;
struct node *ptr;
cout<<"\nPUSH Operation\n";
cout<<"Enter a number to insert: ";
cin>>value;
ptr=new node;
ptr->data=value;
ptr->next=NULL;
if(top!=NULL)
ptr->next=top;
top=ptr;
cout<<"\nNew item is inserted to the stack!!!";
getch();
}
// POP Operation
void stack::pop()
{
struct node *temp;
if(top==NULL)
{
cout<<"\nThe stack is empty!!!";
getch();
return;
}
temp=top;
top=top->next;
cout<<"\nPOP Operation........\nPoped value is "<<temp->data;
delete temp;
getch();
}
// Balance parenthesis
void stack::balance()
{
char leftparen = '(';
char rightparen = ')';
bool error = false;
char ch;
int value;
struct node *ptr;
cout<<"Enter Stack: ";
cin>>ch;
while (( ch != '\n') && (!error) )
{
if (ch == leftparen)
ptr=new node;
ptr->data=value;
ptr->next=NULL;
if (ch == rightparen)
if (isEmpty(s))
error = true;
else
temp=top;
top=top->next;
cin.get(ch);
}
if ((!error) && isEmpty(s))
cout<<"Valid expression"<<endl;
else
cout <<"Invalid Expression"<<endl;
}
// Show stack
void stack::show()
{
struct node *ptr1=top;
cout<<"\nThe stack is\n";
while(ptr1!=NULL)
{
cout<<ptr1->data<<" ->";
ptr1=ptr1->next;
}
cout<<"NULL\n";
getch();
}
// Main function
int main()
{
stack s;
int choice;
while(1)
{
cout<<"\n-----------------------------------------------------------";
cout<<"\n\t\tSTACK USING LINKED LIST\n\n";
cout<<"1:PUSH\n2:POP\n3:BALANCE\n4:DISPLAY STACK\n5:EXIT";
cout<<"\nEnter your choice(1-4): ";
cin>>choice;
switch(choice)
{
case 1:
s.push();
break;
case 2:
s.pop();
break;
case 3:
s.balance();
break;
case 4:
s.show();
break;
case 5:
exit(0);
break;
default:
cout<<"Please enter correct choice(1-4)!!";
getch();
break;
}
}
return 0;
}