void AddNewItem(PItem* head, PItem* tail, int n, int a, float b)
{
    PItem curr, prev = NULL, temp = (PItem)malloc(sizeof(struct Item));
    int pos = 1;
    if (temp == NULL)
    {
        DeleteList(head);
        Error_Msg("Memmory!");
    }
    temp->num = a;
    temp->price = b;
    curr = *head;
    if (head != NULL)
    {
        while (curr->next != NULL && pos != n)
        {
            prev = curr;
            curr = curr->next;
            pos++;
        }
        if (pos == 1) // Set NewItem as head
        {
            temp->next = *head;
            *head = temp;
        }
        else if (curr->next == NULL && n == pos + 1) // Set NewItem as tail
        {
            (*tail)->next = *tail;
            *tail = temp;
        }
        else if (n > pos + 1)
            return; //Position not valid
        else
        {
            prev->next = temp;
            temp->next = curr;
        }
    }
}