Question

Write a C++ program to implement a queue using linked lists. You can use the queue data structure from the Standard Template Library (STL).

The program should provide the following functionality:

• Enqueue data into queue
• Dequeue data from queue
• Print data at the front
• Print data at the back
• Print the entire queue
• Check if the queue is empty
• Print the number of elements in the queue

Test your program using at least the following test cases (considering the queue includes integers):

1. Check if the queue is empty
2. Enqueue 7 into the queue
3. Enqueue 4 into the queue
4. Check if the queue is empty
5. Dequeue data form the queue.
6. Print the number of elements in the queue
7. Enqueue 5 into the queue.
8. Print the number of elements in the queue
9. Check if the queue is empty
10. Print data at the front
11. Print data at the back
12. Print entire queue

Answer 1

CODE IN C++ :

#include<iostream>
using namespace std;
class Node { // Node class for linked list
public :
int data;
Node* next;

Node(int data) {
this -> data = data;
next = NULL;
}
};
class Queue // Queue class for queue using linked list
{
Node* head;
Node* tail;
int size; // size of the queue

   public :

   Queue() {
head = NULL;
tail = NULL;
size = 0;
   }

   void enqueue(int data) // enqueue data into queue
   {
   Node * newNode = new Node(data);
   if( head == NULL )
   {
   head = newNode;
tail = newNode;
}
else
{
tail->next = newNode;
tail = newNode;
}
size++;
   }

   void getSize() { // print the number of elements in the queue.
cout << size << endl;
   }

   bool isEmpty() { // check if queue is empty
return size==0;
   }

   int dequeue() { // dequeue data from the queue
if(head != NULL)
{
int ans = head->data;
Node *temp = head;
delete temp;
head = head->next;
size--;
return ans;
}
   }

   void front() // print data at the front
   {
if(head != NULL)
{
cout << head->data << endl;
}
   }
   void back() // print data at the back
   {
   if(tail != NULL)
{
cout << tail->data << endl;
}
   }
};

// Driver's code to test the program
int main()
{
Queue q1;
cout << "Is the queue empty ? " << q1.isEmpty() << endl; // 1 implies yes, 0 implies no and it will give 1 because initially size is 0
q1.enqueue(7); // 7 pushed into the queue
q1.enqueue(4); // 4 pushed into the queue
cout << "Is the queue empty ? " << q1.isEmpty() << endl; // 1 implies yes, 0 implies no and it will give 0 because queue is no more empty
q1.dequeue(); // 7 removed from the queue
cout << "The number of elements in the queue : ";
q1.getSize(); // Answer should be 1 because only 4 is present
q1.enqueue(5); // 5 pushed into the queue
cout << "The number of elements in the queue : ";
q1.getSize(); // Answer should be 2 because 4 and 5 are present
cout << "Is the queue empty ? " << q1.isEmpty() << endl; // 1 implies yes, 0 implies no and it will give 0 because 4 and 5 are present
cout << "Data at the front is : ";
q1.front();// it should print 4
cout << "Data at the back is : ";
q1.back(); // it should print 5;
cout << "The entire queue is : ";
while(!q1.isEmpty()) // perform while it is non-empty
{
cout << q1.dequeue() << " ";
}

}

OUTPUT SNIPPET :

Is the queue empty ? 1 Is the queue empty ? O The number of elements in the queue : 1 The number of elements in the queue : 2 Is the queue empty ? 0 Data at the front is : 4 Data at the back is : 5 The entire queue is : 4 5 Process returned @ (@x@> execution time Press any key to continue. : 0.095 S

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