Write a program to implement queue using linked list.

Queue Implementation in C

#include stdio.h
#include stdlib.h

struct node
{
    int data;
    struct node *next;
} * head, *temp, *travel, *ptr;

void print()
{
    travel = head;
    if (travel == NULL)
    {
        printf("Linked-List is empty.\n");
    }
    else
    {
        while (travel != NULL)
        {
            printf("%d ", travel->data);
            travel = travel->next;
        }
    }
}

void add_at_last(int data)
{

    struct node *new_node = (struct node *)malloc(sizeof(struct node));
    struct node *last = head;
    new_node->data = data;
    new_node->next = NULL;
    if (head == NULL)
    {
        head = new_node;
        return;
    }

    while (last->next != NULL)
        last = last->next;

    last->next = new_node;
}

void del_first()
{
    if (head == NULL)
    {
        printf("\nLinked-List is Empty..");
    }
    else
    {
        printf("Deleted elemnt is %d", head->data);
        ptr = head;
        head = head->next;
        free(ptr);
        ptr = NULL;
    }
}

void main()
{
    int choice, n, t, key;

    while (1)
    {
        printf("\n1.INSERT ELEMENT INTO QUEUE\n2.DELETE ELEMENT FROM QUEUE\n3.DISPLAY QUEUE\n4.EXIT");
        scanf("%d", &choice);

        switch (choice)
        {
        case 1:
            printf("Enter the element::");
            scanf("%d", &t);
            add_at_last(t);
            break;
        case 2:
            del_first();
            break;
        case 3:
            print();
            break;
        case 4:
            exit(0);
        default:
            printf("\nEnter valid choice");
            break;
        }
    }
}