using System;

​

namespace InvoiceApp

{

    // Class to represent an invoice for an item sold at a hardware store

    public class Invoice

    {

        // Automatic properties for Invoice class

        public string PartNumber { get; set; }

        public string PartDescription { get; set; }

        private int quantity;

        private decimal pricePerItem;

​

        // Constructor to initialize the invoice details

        public Invoice(string partNumber, string partDescription, int quantity, decimal pricePerItem)

        {

            PartNumber = partNumber;

            PartDescription = partDescription;

            Quantity = quantity; // Use property to validate

            PricePerItem = pricePerItem; // Use property to validate

        }

​

        // Property for quantity with validation

        public int Quantity

        {

          get { return quantity; }

          set

   {

       // Only set quantity if the value is non-negative

          if (value >= 0)

   {

          quantity = value;

                }

            }

        }

        public decimal PricePerItem

        {

         get { return pricePerItem; }

         set

            {

         // Only set price if the value is non-negative

         if (value >= 0)

                {

         pricePerItem = value;

                }

            }

        }

​

        // Method to calculate the total invoice amount

        public decimal GetInvoiceAmount()

        {

            return Quantity * PricePerItem;

        }

    }

​

    // Test application to demonstrate the capabilities of the Invoice class

    class InvoiceTest

    {

        static void Main(string[] args)

        {

            // Create three different invoice instances

            Invoice invoice1 = new Invoice("1", "Hamer", 5, 9.99m);

            Invoice invoice2 = new Invoice("2", "Screw", 3, 7.50m);

            Invoice invoice3 = new Invoice("3", "Driller", -2, 150.00m); // Negative quantity should be ignored

​

            // Display the details and total amounts of the invoices

            DisplayInvoice(invoice1);

            DisplayInvoice(invoice2);

            DisplayInvoice(invoice3);

        }

​

        // Method to display invoice details and amount

        static void DisplayInvoice(Invoice invoice)

        {

            Console.WriteLine($"Part Number: {invoice.PartNumber}");

            Console.WriteLine($"Part Description: {invoice.PartDescription}");

            Console.WriteLine($"Quantity: {invoice.Quantity}");

            Console.WriteLine($"Price per Item: {invoice.PricePerItem:C}");

            Console.WriteLine($"Invoice Amount: {invoice.GetInvoiceAmount():C}");

            Console.WriteLine(new string('_', 30)); // Separator for clarity

        }

    }

}