ifndef queueLL_H #define queueLL_H #include class queueLL { private: //defining an inner node class class node { public: //has integer data int data; //reference to next node node* next; //constructor taking value for data field node(int dat) { data = dat; next = NULL; } }; //references to front and rear nodes of the queue node* front, * rear; public: //constructor to initialize empty queue queueLL() { front = NULL; rear = NULL; } ~queueLL() // Deconstructor of queueLL to free space { //continuously dequeueing the queue until empty while (!empty()) { dequeue(); } } // Checks if the received queue is empty bool empty() const { return front == NULL; } //Adds the enqueued item to back of queue void enqueue(int x) { //if queue is empty, creating a new node and saving it as both front //and rear if (empty()) { front = new node(x); rear = front; } //otherwise appending new node as next of rear and updating rear else { rear->next = new node(x); rear = rear->next; } } //Removes and return first item from queue int dequeue() { //taking a reference to front node node* f = front; //advancing front front = front->next; //if front is now NULL, setting rear to NULL too if (front == NULL) { rear = NULL; } //fetching data of f int data = f->data; //deleting f delete f; //returning removed data return data; } }; #endif

Question

How do I make my queueLL.h into a template class and a decimation method?

////////////////////////////

#ifndef queueLL_H
#define queueLL_H
#include<iostream>

class queueLL
{
private:
//defining an inner node class
class node
{
public:
//has integer data
int data;
//reference to next node
node* next;
//constructor taking value for data field
node(int dat) {
data = dat;
next = NULL;
}
};
//references to front and rear nodes of the queue
node* front, * rear;

public:
//constructor to initialize empty queue
queueLL()
{
front = NULL;
rear = NULL;

}

~queueLL() // Deconstructor of queueLL to free space
{
//continuously dequeueing the queue until empty
while (!empty()) {
dequeue();
}
}

// Checks if the received queue is empty
bool empty() const
{
return front == NULL;
}

//Adds the enqueued item to back of queue
void enqueue(int x)
{
//if queue is empty, creating a new node and saving it as both front
//and rear
if (empty()) {
front = new node(x);
rear = front;
}
//otherwise appending new node as next of rear and updating rear
else {
rear->next = new node(x);
rear = rear->next;
}

}

//Removes and return first item from queue
int dequeue()
{
//taking a reference to front node
node* f = front;
//advancing front
front = front->next;
//if front is now NULL, setting rear to NULL too
if (front == NULL) {
rear = NULL;
}
//fetching data of f
int data = f->data;
//deleting f
delete f;
//returning removed data
return data;
}
};

#endif

Answer 1

#include <iostream>
using namespace std;

typedef int entrytype;

class node
{
public:
    entrytype nodedata;
    node *next;

    node()
    {
    }
    node(entrytype nodedata, node *next = nullptr)
    {
        this->nodedata = nodedata;
        this->next = next;
    }
};

class queue
{
private:
    node *first;
    node *last;
    int Size;

public:
    // constructor
    queue()
    {
        first = last = nullptr;
        Size = 0;
    }

    // destructor
    ~queue()
    {
        node *curr = first;
        // iterate over the list and delete the nodes
        while (curr != nullptr)
        {
            node *toDel = curr;
            curr = curr->next;
            delete toDel;
        }
        first = last = nullptr; // set the first AND LAST as null
        Size = 0;               // set the size to zero
    }

    // method to append a node to the end of the queue
    bool append(entrytype value)
    {
        node *newNode = new node(value);
        // return false in case of overflow
        if (newNode == nullptr)
        {
            return false;
        }
        // if there is no node in the list
        if (first == nullptr)
        {
            first = newNode; // make this the head node
            last = first;    // this is also the last node
        }
        // if there is atleast one node in the list
        // add it to the end of the list and update the tail
        else
        {
            last->next = newNode;
            last = last->next;
        }
        // update the size
        Size++;
        return true;
    }

    // method to access the front element of the queue
    bool front(entrytype &value)
    {
        // if queue is empty : return the underflow error
        if (first == nullptr)
        {
            return false;
        }
        // else set the value as first element's value
        value = first->nodedata;
        return true;
    }

    // method to delete the first element of the queue
    bool pop()
    {
        // if queue is empty : return underflow error code
        if (first == nullptr)
        {
            return false;
        }
        // else remove the first element of the queue
        node *toPop = first; // access the first element
        // move first to next node
        first = first->next;
        // if first became null : it means there was a single node in the list
        // so make last null as well.
        if (!first)
            last = nullptr;
        delete toPop; // delete the first node
        // update the Size
        Size--;
        return true; // return true if operation was successful
    }

    // method to get the current size of the queue
    int size()
    {
        return Size;
    }

    // method to check if given element exists in the queue
    bool find(entrytype target)
    {
        for (node *curr = first; curr != nullptr; curr = curr->next)
        {
            if (curr->nodedata == target) // if value is found return true
                return true;
        }
        return false; // return false
    }
};

int main()
{
    queue *q = new queue; // create a new queue

    // add the even elements to the queue
    for (entrytype x = 8; x <= 398; x += 2)
    {
        q->append(x);
    }

    entrytype frontEl; // to store the front of the queue

    // get the front of the queue
    q->front(frontEl);
    cout << "Front of the queue: " << frontEl << endl;

    // remove the first two elements of the queue
    cout << "Popped 2 elements from the queue\n";
    q->pop();
    q->pop();

    // check if 8 exists in the queue
    cout << "Does 8 exists in the queue? " << q->find(8) << endl;
    // check if 200 exists in the queue
    cout << "Does 200 exists in the queue? " << q->find(200) << endl;

    // report the size of the queue
    cout << "Current size of the queue: " << q->size() << endl;

    // remove 10 elements from the queue
    for (int i = 0; i < 10; i++)
        q->pop();
    cout << "Popped 10 elements from the queue\n";

    // get the new size of the queue
    cout << "Updated size of the queue: " << q->size() << endl;

    // get the front of the queue
    q->front(frontEl);
    cout << "Front of the queue: " << frontEl << endl;

    return 0;
}

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