Queue with linked list

// Online C compiler to run C program online
#include <stdio.h>
#include <stdlib.h>

struct Node {
    int data;
    struct Node *next;
} *start = NULL;

int maxsize = 5;
int length = 0;

void Queue(int d) {
    struct Node *temp;
    temp = (struct Node *)malloc(sizeof(struct Node));
    temp->data = d;
    temp->next = NULL;
    if (start == NULL) {
        start = temp;
        printf("Queue Created successfully");
        length = 1;
    }
}

int size() {
    return length;
}

int isEmpty() {
    return size() == 0;
}

void enqueue(int d) {
    struct Node *temp;
    temp = (struct Node *)malloc(sizeof(struct Node));
    temp->data = d;
    temp->next = NULL;
    if (size() < maxsize) {
        temp->next = start;
        start = temp;
        length += 1;
    }
    else {
        printf("Queue overflow");
    }
}

void dequeue() {
    struct Node *temp, *ptr;
    if (isEmpty()) {
        printf("Queue underflow");
    }
    else {
        ptr = start;
        while (ptr->next->next != NULL) {
            ptr = ptr->next;
        }
        temp = ptr->next;
        ptr->next = NULL;
        printf("Element deleted %d", temp->data);
        free(temp);
        length -= 1;
    }
}

int main(){
    int choice, data=0;
    while (choice!=5) {
        printf("\n1. Create a Queue");
        printf("\n2. Enqueue an element");
        printf("\n3. Dequeue an element");
        printf("\n4. Get Queue Size");
        printf("\n5. Exit");

        printf("\n Enter a choice");
        scanf("%d", &choice);

        switch(choice) {
            case 1:
                    printf("Enter a start element : ");
                    scanf("%d", &data);
                    Queue(data);
                    break;
            case 2:
                    if (start == NULL) {
                        printf("Create a Queue First");
                    }
                    else{
                        printf("Enter a start element : ");
                        scanf("%d", &data);
                        enqueue(data);
                    }
                    break;
            case 3:
                    dequeue();
                    break;
            case 4:
                    size();
                    break;
            case 5: break;
            default: break;
        }
    }
}