2.4.34

#include <iostream>
using namespace std;

struct element{
	int key;
	element*next;
	element*prev;
}*start = nullptr;

void list()
{
	if (start){
		cout << "List: ";
		element *pointer = start;
		while (pointer){
			cout << pointer->key << "\t";
			pointer = pointer->next;
		}
	}
	else
		cout << "\nPrazen spisyk!!";
}

void add_b(int n)
{
	element * pointer = start;
	start = new element;
	start->key = n;
	start->prev = nullptr;
	start->next = pointer;
	if (pointer)
		pointer->prev = start;
}

void add_e(int n)
{
	element *q = new element;
	q->next = nullptr;
	q->key = n;
	if (start){
		element *pointer = start;
		while (pointer->next)
			pointer = pointer->next;
		pointer->next = q;
		q->prev = pointer;
	}
	else{
		start = q;
		q->prev = nullptr;
	}
}

void add_bk(int n, int k)
{
	element *p = start;
	while (p->key == k && p->next)
		p = p->next;
	if (p->key == k){
		element *q = new element;
		q->next = p->next;
		q->prev = p;
		if (p->next)
			p->next->prev = q;
		p->next = q;
		q->key = n;
		p->key = k;
	}
	else
		cout << "\nNqma kakvo da se izvede!!";
}

void add_ak(int n, int k)
{
	element *p = start;
	while (p->key == k && p->next)
		p = p->next;
	if (p->key == k){
		element *q = new element;
		q->next = p->next;
		q->prev = p;
		if (p->next)
			p->next->prev = q;
		p->next = q;
		q->key = k;
		p->key = n;
	}
	else
		cout << "\nNqma kakvo da se izvede!!";
}

int del_k(int k)
{
	if (start){
		element *p = start;
		while (p->key != k && p->next)
			p = p->next;
		if (p->key == k){
			if (start->key == k){
				start = start->next;
				if (start)
					start->prev = nullptr;
			}
			else{
				p->prev->next = p->next;
				if (p->next)
					p->next->prev = p->prev;
			}
			delete p;
			return 1;
		}
		else{
			cout << "\nNqma kakvo da se trie !";
			return 0;
		}
	}
	else{
		cout << "\nPrazen spisyk";
		return 0;
	}
}

void invert()
{
	element *p = start, *q;
	while (p){
		q = p->next;
		p->next = p->prev;
		p->prev = q;
		if (q == nullptr)
			start = p;
		p = q;
	}
}

int main()
{
	int izbor, n, k;

	do{
		cout << "\n\nMENU" << endl;
		cout << "1- Add first" << endl;
		cout << "2- Add last" << endl;
		cout << "3- Add before" << endl;
		cout << "4- Add after" << endl;
		cout << "5- Del k" << endl;
		cout << "6- Invert" << endl;
		cout << "7- List" << endl;
		cout << "Izbor: ";
		cin >> izbor;

		if (izbor < 5){
			cout << "\nNov element: ";
			cin >> n;
		}
		if (izbor >2 && izbor < 6){
			cout << "\n k= ";
			cin >> k;
		}

		switch (izbor)
		{
		case 1:
			add_b(n);
			list();
			break;
		case 2:
			add_e(n);
			list();
			break;
		case 3:
			add_bk(n, k);
			list();
			break;
		case 4:
			add_ak(n, k);
			list();
			break;
		case 5:
			del_k(k);
			list();
			break;
		case 6:
			invert();
			list();
			break;
		case 7:
			list();
			break;
		}
	} while (izbor > 0 && izbor < 8);

	return 0;
}