//Syed Rais Ahmad
//Assignment # 5 Quest 6
//Circular List.Del every 2nd,free all nodes, return sum of ints

#include<iostream.h>

//A node in a list
class llistItem
{
public:
	int item;
	llistItem * nxtItem;
};


//circular List
class cList
{
private:
	llistItem *rear;
public:
	cList(); 
	~cList() {delete rear;}; 
	void DelEvery2nd(void);
	bool Insert(int);
	int Remove();
	bool isEmpty();
	void printAll();
	void freeAll();
	int total();
};


//create rear and put NULL values in it.
cList::cList()
{
	rear = new llistItem;
	rear->nxtItem=NULL;//Empty cList
}


//return the total of all integers in list
int cList::total()
{
	if (!isEmpty())
	{
		llistItem * ptr=rear->nxtItem;
		int total=ptr->item;
		while((ptr=ptr->nxtItem)!=rear->nxtItem) total+=ptr->item;
		return total;
	}
	return 0;
}


//Return an item. -1 if stack is empty
int cList::Remove()
{
	if (!isEmpty())
	{
		llistItem * front,* temp;
		int i=0;
//front gets the address of next node from rear		
		front=rear->nxtItem->nxtItem;
//if only one node is remaining then front = rear;
		if (front==rear->nxtItem) 
		{
			i=front->item; 
			delete front;
			rear->nxtItem=NULL; //empty the cList
			return i;
		}
//temp gets the about-to-be front node's address.
		temp=front->nxtItem;
		i=front->item;
//rear node now points to a new front node.
		rear->nxtItem->nxtItem=temp;
		delete front;
		return i;
	}
	return -1;
}


//Delete Every Second Entry from list
void cList::DelEvery2nd()
{
	llistItem * ptr=rear->nxtItem,*temp;
	while(1)
	{
		temp=ptr->nxtItem->nxtItem;
		if (ptr->nxtItem==rear->nxtItem) break;
		else delete ptr->nxtItem;
		ptr->nxtItem=temp;
		if ((ptr=ptr->nxtItem)==rear->nxtItem) break;

	}
}


//free all nodes in cList
void cList::freeAll()
{
	while(!isEmpty()) Remove();
}


//print all values stored in list
void cList::printAll()
{
	if (!isEmpty())
	{
	llistItem * ptr;
	ptr=rear->nxtItem;
	while((ptr=ptr->nxtItem)!=rear->nxtItem) cout << '\n' << ptr->item;
	cout << '\n' << ptr->item;
	}
}


//Insert an int to a cList
bool cList::Insert(int insInt)
{
	llistItem * ptr,*temp;
//insert will always need new node with new integer value in it.		
	ptr=new llistItem;
	ptr->item=insInt;

	if (isEmpty())
	{
//node points to itself
		ptr->nxtItem=ptr;
		rear->nxtItem=ptr;
	}
	else
	{
//temp holds value for node next to rear node.
		temp=rear->nxtItem->nxtItem;
//rear is now the new node, just inserted.
		rear->nxtItem->nxtItem=ptr;
		ptr->nxtItem=temp;
//rear points to a newly inserted node.
		rear->nxtItem=ptr;
	}
		return true;
}

//is cList Empty
bool cList::isEmpty()
{
	return (rear->nxtItem==NULL)? true : false;
}


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

main()
{
	cList q;int i=0;
	for(;i<10;i++)
	q.Insert(i);
	
//print the original list
	cout << "\nList is:";
	q.printAll();
//del every other
	cout << "\nDeleting Every other Element:\n";
	q.DelEvery2nd();
	cout << "\nList becomes:" ; 
	q.printAll();
//total the value of all nodes	
	cout  << "\nTotal is:\n";
	cout << q.total() << '\n';
//Free all nodes
	cout << "\bFreeing All nodes...\nList becomes:\n";
	q.freeAll();
	q.printAll();

	return 0;

}