How to keep adding to exsiting textbox on a form? input, save, clear and repeat?

See more:

C#

Visual-Studio

GUI

FileStream

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;
using System.IO;

namespace Angie_assignment
{
public partial class frmInventory : Form
{
//declare public variables and input user info into filestream
const string FILENAME = "INVENTORY.txt";
FileStream outFile = new FileStream(FILENAME, FileMode.Append, FileAccess.Write);

public frmInventory()
{
InitializeComponent();
}

private void btnAddSave_Click(object sender, EventArgs e)
{
//declare vairables
string description;
string price;
string code;
StreamWriter writer = new StreamWriter(outFile); // open text file

do
{
//input data
code = txtBoxCode.Text;
description = txtBoxDrscription.Text;
price = txtBoxCost.Text;

//write in info to text file
writer.WriteLine(code);
writer.WriteLine(description);
writer.WriteLine(price);

txtBoxCode.Text = "";
txtBoxDrscription.Text = "";
txtBoxCost.Text = "";
txtBoxCode.Focus();
}
while (rbtnLastEntry.Checked == false);


//close file
writer.Close();
outFile.Close();

}

}
}


I tried to do a loop and added a radio button that states whether the user is at their last entry to work around but still no use. Any help would be appreciated! :D