Display Button

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Indexers
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void textBox2_TextChanged(object sender, EventArgs e)
        {

        }

        private void btnDisplay_Click(object sender, EventArgs e)
        {

            Invoice inv = new Invoice(txtInvoiceNumber.Text, txtDescription.Text, int.Parse(txtQuantity.Text), Convert.ToDecimal(txtPrice.Text));
            InvoiceList myList = new InvoiceList();

            myList.Add(inv);
            decimal x = myList[0].GetInvoiceAmount();
            txtOutput.Text += inv.ToString() + " , " + " Invoice Amount is: " + x.ToString("c")+ "\r\n";


        }

        private void Form1_Load(object sender, EventArgs e)
        {





        }

        private void btnExit_Click(object sender, EventArgs e)
        {
            string message = "Are you sure you want to close the form ?";

            DialogResult button = MessageBox.Show(message, "Confirm",
                MessageBoxButtons.YesNo);
            if (button == DialogResult.Yes)
            {
                this.Close();
            }

        }
    }
}