//Write a program to implement Queue using Linked List.
#include<stdio.h>
#include<stdlib.h>
// Define the structure for a node in the linked list
typedef struct node
{
 int data;
 struct node *link;
} NODE;
// Declare global pointers for the front, rear, current node, and display node
NODE *front = NULL, *rear = NULL, *s, *ptr, *display;
// Main function
int main()
{
 int no;
 char c;
 // Display program information
 printf("\n\tPROGRAM TO INSERT, DELETE AND DISPLAY ELEMENTS TO QUEUE USING LINKEDLIST");
 printf("\t\t..............................................................\n\n");
 // Menu-driven loop
 do
 {
 // Display menu options
 printf("\t\t\t\tMENU");
 printf("\n\t\t1. INSERT\n\t\t2. DELETE\n\t\t3. DISPLAY\n\t\t4. EXIT\n\t\tEnter your choice: ");
 scanf("%d", &no);
 // Switch based on the user's choice
 switch (no)
 {
 case 1:
 // Insert operation
 ptr = (NODE*)malloc(sizeof(NODE));
 printf("\t\tEnter the element: ");
 scanf("%d", &ptr->data);
 ptr->link = NULL;
 // Check if the queue is empty
 if (rear == NULL)
 {
 front = ptr;
 rear = ptr;
 }
 else
 {
 rear->link = ptr;
 rear = ptr;
 }
 break;
 case 2:
 // Delete operation
 if (front == NULL)
 printf("\t\tQueue is empty\n");
 else
 {
 s = front;
 printf("\t\tDeleted Element is %d\n", front->data);
 front = front->link;
 free(s);
 // If the queue becomes empty after deletion
 if (front == NULL)
 rear = NULL;
 }
 break;
 case 3:
 // Display operation
 if (front == NULL)
 printf("\t\tQueue is empty\n");
 else
 {
 printf("\t\tQueue elements are");
 display = front;
 // Traverse the queue and display elements
 while (display != NULL)
 {
 printf(" %d", display->data);
 display = display->link;
 }
 printf("\n");
 }
 break;
 case 4:
 // Exit the program
 exit(0);
 }
 // Prompt the user to continue
 printf("\t\tDo you want to continue(y/n) ");
 scanf(" %c", &c);
 } while (c == 'y' || c == 'Y');
 return 0;
}