//Syed Rais Ahmad
//Assignment # 5 Quest 1
//empty,push,pop and popandtest using dynamic storage.

#include<iostream.h>

//A node in Link List.
class llistItem
{
public:
	int item;
	llistItem * nxtItem;
};


//Link List 
class Stack
{
private:
	llistItem * head;
public:
	Stack(); 
	~Stack() {delete head;}; 
	bool push(int);
	int popNTest();
	int pop();
	bool Empty();
};


//create head and put NULL values in it.
Stack::Stack()
{
	head = new llistItem; 
	head->nxtItem=NULL;
	head->item=NULL;
}


//Pops an item is on stack Top.
int Stack::pop()
{
		int i=0;
		llistItem * ptr=head->nxtItem->nxtItem; 
		i=head->nxtItem->item;
		delete head->nxtItem;
		head->nxtItem=ptr;
		return i;
}


//Return an item is on stack Top. -1 if stack is empty
int Stack::popNTest()
{
	
	if (head->nxtItem)
	{
		int i=0;
		llistItem * ptr=head->nxtItem->nxtItem; 
		i=head->nxtItem->item;
		delete head->nxtItem;
		head->nxtItem=ptr;
		return i;
	}
	return -1;
}



//push an int on stack
bool Stack::push(int insInt)
{
		llistItem * ptr=head, * temp;
		temp=ptr->nxtItem;
		ptr->nxtItem=new llistItem;
		ptr->nxtItem->item=insInt;
		ptr->nxtItem->nxtItem=temp;
		return true;
}

//is Stack Empty
bool Stack::Empty()
{
	return (head->nxtItem)? false : true;
}


//------- Program's main flow starts ---------------------------

main()
{
	Stack l;
	int i=0;
	l.push(2);
	l.push(11);

	

	cout << "\nPushed 2, 11. Pop Returns: " << l.pop();
	cout << "\nEmpty() returns: " << l.Empty();
	cout << "\nSecond Pop returns: " << l.pop();
	cout << "\nEmpty() returns: " << l.Empty();
	cout << "\npopandTest() returns :" << l.popNTest() << '\n';
	return 0;

}