9.queue

//IMP
//queue empty:- (head=null)
//deq is to delete element from front
//enq is to insert element from back

//Make a singly linked list by class node and class ll
//Make data memebers private and use friend class ll; in node class.
//In class ll, have only head
//
//Member fns:
//void ins(int n);
//void del();
//void disp();
//bool isempty();

//create node* nn=new node;
//nn->prn=n;
//nn->next=NULL; in insert fn

//in insert:
//1. check if empty, if yes just do head=nn;
//2. if not, have while loop to reach end of list n then insert.

//in delete:
//1.check if empty, display del not possible
//2. if not, delete.

#include<iostream>
using namespace std;
class node
{
	int prn;
	node* next;
public:
	node()
	{
		prn = 0;
	}
	friend class ll;
};
class ll
{
	node* head;
public:
	ll()
	{
		head = NULL;
	}
	void ins(int n);
	void del();
	void disp();
	bool isempty();
};
bool ll::isempty()
{
	if (head == NULL)
		return true;

	return false;
}
void ll::ins(int n)
{
	node* nn = new node;
	nn->prn = n;
	nn->next = NULL;

	if (isempty())
	{
		head = nn;
	}
	else
	{
		node* p = head;
		while (p->next != NULL)
		{
			p = p->next;
		}
		p->next = nn;
	}
	cout << "---Inserted in Queue---" << endl;
}
void ll::del()
{
	if (isempty())
		cout << "---Nothing to delete--" << endl;

	else
	{
		node* p = head;
		head = head->next;
		delete(p);
		cout << "---Deleted from Queue---" << endl;
	}
}
void ll::disp()
{
	if (isempty())
		cout << "---Nothing to Display---" << endl;
	else
	{
		node* start = head;
		while (start != NULL)
		{
			cout << start->prn << endl;
			start = start->next;
		}
	}
}
int main()
{
	int ch;
	int ele;
	ll a;
	do
	{
		cout << "\n\t Enter ur Choice" << endl;
		cout << "\n\t 1.Add Job" << endl;
		cout << "\n\t 2.Delete Job" << endl;
		cout << "\n\t 3.Display " << endl;
		cout << "\n\t 4.Exit" << endl;

		cin >> ch;

		switch (ch)
		{
		case 1:
			cout << "Enter PRN of Job" << endl;
			cin >> ele;
			a.ins(ele);
			break;

		case 2:
			a.del();
			break;

		case 3:
			cout << "---Displaying Queue---" << endl;
			a.disp();
			break;

		case 4:
			cout << "\n\tThank You!!!" << endl;
			break;

		default:cout << "Invalid Choice" << endl;
		}
	} while (ch != 4);
	
	cout << "\n\tExit" << endl;
	return 0;
}