queueUsingLinkedList.cpp

#include <iostream>
using namespace std;

struct node
{
   int data;
   struct node *next;
};

struct node *front = NULL;
struct node *rear = NULL;
struct node *temp;

void Insert()
{
   int val;

   cout << "Insert the element in queue : " << endl;
   cin >> val;

   if (rear == NULL)
   {
      rear = (struct node *)malloc(sizeof(struct node));
      rear->next = NULL;
      rear->data = val;
      front = rear;
   }
   else
   {
      temp = (struct node *)malloc(sizeof(struct node));
      rear->next = temp;
      temp->data = val;
      temp->next = NULL;
      rear = temp;
   }
}

void Delete()
{
   temp = front;
   if (front == NULL)
   {
      cout << "Underflow" << endl;
      return;
   }
   else if (temp->next != NULL)
   {
      temp = temp->next;
      cout << "Element deleted from queue is : " << front->data << endl;
      free(front);
      front = temp;
   }
   else
   {
      cout << "Element deleted from queue is : " << front->data << endl;
      free(front);
      front = NULL;
      rear = NULL;
   }
}

void Display()
{
   temp = front;
   if ((front == NULL) && (rear == NULL))
   {
      cout << "Queue is empty" << endl;
      return;
   }
   cout << "Queue elements are: ";
   while (temp != NULL)
   {
      cout << temp->data << " ";
      temp = temp->next;
   }
   cout << endl;
}

int main()
{
   int ch;

   cout << "1) Insert element to queue" << endl;
   cout << "2) Delete element from queue" << endl;
   cout << "3) Display all the elements of queue" << endl;
   cout << "4) Exit" << endl;

   do
   {
      cout << "Enter your choice : " << endl;
      cin >> ch;
      switch (ch)
      {
      case 1:
         Insert();
         break;
      case 2:
         Delete();
         break;
      case 3:
         Display();
         break;
      case 4:
         cout << "Exit" << endl;
         break;
      default:
         cout << "Invalid choice" << endl;
      }
   } while (ch != 4);
   return 0;
}