#include <iostream>
#include <stdlib.h>

using namespace std;

class unit
{
public:
	unit(int data);                  //constructor
	virtual ~unit();                 //destructor
	void push(int data);
	int getData();
	unit* getNext();
	unit* findElement(int data);
	void addToTheEnd(int data);
	void deleteLast();

private:
	unit* next;
	int data;
};

unit::unit(int data)
{
	this->data = data;
	next = NULL;
}

unit::~unit()
{
	delete next;
}

void unit::push(int data)
{
	unit* element = new unit(this->data);
	element->next = this->next;
	this->next = element;
	this->data = data;
}

int unit::getData()
{
	return data;
}

unit* unit::getNext()
{
	return this->next;
}

unit* unit::findElement(int data)
{
	unit* selected = this;
	while (selected->getData() != data)
	{
		selected = selected->getNext();
	}
	return selected;
}

void unit::addToTheEnd(int data)
{
	unit* newData = new unit(data);
	unit* selected = this;
	while (selected->next != NULL)
	{
		selected = selected->next;
	}
	selected->next = newData;
}

void unit::deleteLast()
{
	unit* selected = this;
	while (selected->next != 0)
	{
		selected = selected->next;
	}
	selected = NULL;
}

class list
{
public:
	list();
	~list();
	int getLenght();
	void print();
	void add(int data);
	void addToFront(int data);
	void insertIn(int data, int number);
	void deleteLast();
	unit* findUnit(int data);
	unit* getByNumber(int number);
private:
	int lenght;
	unit* root;
};

list::list()
{
	lenght = 0;
	root = NULL;
}

list::~list()
{
	delete root;
}

int list::getLenght()
{
	return lenght;
}

void list::print()
{
	unit* selected = root;
	if (lenght != 0)
	{
		while (selected->getNext() != NULL)
		{
			cout << selected->getData() << endl;
			selected = selected->getNext();
		}
		cout << selected->getData() << endl;
	}
}

void list::add(int data)
{
	if (lenght != 0)
	{
		root->addToTheEnd(data);
	}
	else
	{
		root = new unit(data);
	}
	lenght++;
}

void list::addToFront(int data)
{
	if (lenght != 0)
	{
		root->push(data);
	}
	else
	{
		root = new unit(data);
	}
	lenght++;
}

void list::insertIn(int data, int number)
{
	if (lenght < number || number < 0)
	{
		cout << "this unit doesn't exist";
	}
	else
	{
		unit* selected = root;
		int temp = 0;
		while (temp < number)
		{
			selected = selected->getNext();
			temp++;
		}
		selected->push(data);
		lenght++;
	}
}

void list::deleteLast()
{
	if (lenght == 0)
	{
		cout << "list is empty";
	}
	else
	{
		root->deleteLast();
		lenght--;
	}
}

unit* list::findUnit(int data)
{
	if (lenght != 0)
	{
		return root->findElement(data);
	}
	else
	{
		return NULL;
	}
}

unit* list::getByNumber(int number)
{
	if ((number<0) || (number>=lenght))
	{
		return NULL;
	}
	else
	{
		unit* selected = root;
		int temp = 0;
		while (temp < number)
		{
			selected = selected->getNext();
			temp++;
		}
		return selected;
	}
}

int main()
{
	list* mylist = new list();
	for (int i = 0; i < 10; i++)
	{
		mylist->add(i);
	}
	mylist->addToFront(-1);
	mylist->print();
	cout << endl;
	cout << mylist->getByNumber(4)->getData() << endl << endl;
	mylist->insertIn(12, 4);
	mylist->print();
	cout<< mylist->getLenght()<<endl;
    mylist->deleteLast();
	cout<< mylist->getLenght()<<endl;
    delete mylist;
	return 0;
}