public int LineCount()
{
return(LineItems.Count());
}
/// <summary>
/// Outputs string containing the following (replace [] with actual values):
/// Invoice Number: [InvoiceNumber], InvoiceDate: [DD/MM/YYYY], LineItemCount: [Number of items in LineItems]
/// </summary>
public override string ToString()
{
return($"Invoice Number: {InvoiceNumber}, InvoiceDate: {(InvoiceDate == DateTime.MinValue ? string.Empty : InvoiceDate.ToString("dd/MM/yyyy")) }, LineItemCount: {LineItems.Count()}");
}