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#include<stdio.h>
#include<stdlib.h>

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

node *front;
node *rear;
void insert();
void del();
void display();

int main ()
{
    int choice;
    while(choice != 4)
    {
        printf("\n ---Main Menu--- \n");
        printf("\n 1.Insert an element\n 2.Delete an element\n 3.Exit\n ");
        printf("\n Enter your choice (1-3) :");
        scanf("%d", &choice);

        switch(choice)
        {
            case 1: insert();
                    display();
                    break;
            case 2: del();
                    display();
                    break;
            case 3: exit(0);
                    break;
            default: printf("\n Invalid Choice ! \n");
        }
    }
}

void insert()
{
    struct node *ptr;
    int item;

    ptr = (struct node *) malloc (sizeof(struct node));
    if(ptr == NULL)
    {
        printf("\n OVERFLOW \n");
        return;
    }
    else
    {
        printf("\n Enter value : \n");
        scanf("%d", &item);
        ptr -> data = item;
        if(front == NULL)
        {
            front = ptr;
            rear = ptr;
            front -> next = NULL;
            rear -> next = NULL;
        }
        else
        {
            rear -> next = ptr;
            rear = ptr;
            rear->next = NULL;
        }
    }
}

void del()
{
    struct node *ptr;
    if(front == NULL)
    {
        printf("\n UNDERFLOW \n");
        return;
    }
    else
    {
        printf("\n %d is Deleted ", front -> data);
        ptr = front;
        front = front -> next;
        free(ptr);
    }
}

void display()
{
    struct node *ptr;
    ptr = front;
    if(front == NULL)
    {
        printf("\n Queue is Empty !! ");
    }
    else
    {   printf("\n Queue :\n");
        while(ptr != NULL)
        {
            printf(" %d ", ptr -> data);
            ptr = ptr -> next;
        }
    }
    printf("\n");
}