stack array

hi the requirement is i have to use two stacks for input and one for output
apply some binary operation on two stacks and store the result in 3rd stack
here is my code

Code:

# include <iostream>
# include <conio.h>
# include <stack>
using namespace std;
class intstack
{
private:
	int * stackarray;
	int stacksize;	
	int top;
public:
	intstack (int);
	void push ();
	void pop ();
	bool isfull (void);
	bool isempty (void);
	intstack add (intstack & o);
};//end class
intstack::intstack (int size)
{
	stackarray=new int[size];
	stacksize=size;
	top=-1;

}//end definition
void intstack::push ()
{
	if(isfull())
	{
		cout<<"stack is full"<<endl;
	
	}//end if
	else 
	{
		top++;
		for (int i=0;i<stacksize-1;i++)
		{
			cin>>stackarray[top];
		
		}
	
	}

}//end push
void intstack::pop ()
{
	int num;
	if(isempty())
	{
		cout<<"stack is empty"<<endl;
	
	}
	else 
	{
		num=stackarray[top];
		top--;
		cout<<num;
	
	}
}//end 
bool intstack::isfull (void)
{
	bool status;
	if (top==stacksize-1)
	{
		status=true;
	
	}
	else 
	{
		status=false;
	
	}
	return status;

}
bool intstack::isempty (void)
{
	bool status;
	if (top==-1)
	{
		status=true;
	
	}
	else 
	{
		status=false;
	
	}
	return status;

}
intstack intstack::add (intstack & o)
{
	intstack temp(stacksize);

	temp.top=top;
	
	for (int i=0; i<stacksize-1; i++)
	{
		temp.stackarray[i]=stackarray[i]+o.stackarray[i];
		
	
	}
	return (temp);


}
int main ()
{
	int var=0;
	intstack stack1(5),stack2(5),stack3(5);
	cout<<"enter numbers in first stack"<<endl;
	stack1.push ();
	cout<<"enter number in second stack"<<endl;
	stack2.push ();
	stack3=stack2.add (stack1);
	stack3.pop ();
	stack3.pop ();
	stack3.pop ();
	stack3.pop ();
	getch ();
}//

the problem is that when i execute this code it runs but it shows the result of last array element but not others and say "stack is empty".
for example i have entered in first array
1
2
3
4
numbers in 2nd array
5
6
7
8
then it shows
12
stack is empty
stack is empty
stack is empty
can anyone correct my code please

Code:

void intstack::push ()
{
	if(isfull())
	{
		cout<<"stack is full"<<endl;
	
	}//end if
	else 
	{
		top++;
		for (int i=0;i<stacksize-1;i++)
		{
			cin>>stackarray[top];
		
		}
	
	}

}//end push

If you write to the same memory location four times, what are the odds you will actually get to keep all four numbers?

i got it thanks tabstop
now its is working