How to record a custom event upon button click?

I am working on a small binary converter program, and I am adding a feature to it that will record the decimal that they put into a text box before conversion and then record the output of the binary/hex code that it converts to.

I want to use the StreamWriter from System.IO to record the data into a text file that the user can open from the program based upon button click. Sadly, I have no idea how to use the StreamWriter. I will post the code i have below.

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;
using System.IO;

namespace Aspire_Binary_Converter
{
    public partial class mainUI : Form
    {
        public mainUI()
        {
            InitializeComponent();
        }

        private void convertBtn_Click(object sender, EventArgs e)
        {
            string convertingNumTxt = convertNumTxt.Text;

            if (convertingNumTxt.Contains("-"))
            {
                MessageBox.Show("ERROR: Type - SYNTX; The number to be converted may not contain the dash or hyphen.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            else
            {
                if (convertingNumTxt.Contains("."))
                {
                    MessageBox.Show("ERROR: Type - SYNTX; The number to be converted may not contain the period or decimal.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                else
                {
                    if (convertingNumTxt.Contains("()"))
                    {
                        MessageBox.Show("ERROR: Type - SYNTX; The number to be converted may not contain any type of parenthesis or bracket.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    }
                    else
                    {
                        //RECORD KEEPING

                        if (enableRecordCheck.Checked == true)
                        {
                            viewRecordsBtn.Visible = true;
                            this.Update();
                        }
                        
                        if (enableRecordCheck.Checked == false)
                        {
                            viewRecordsBtn.Visible = false;
                            this.Update();
                        }

                        //HEXADECIMAL / BINARY CONVERTER

                        if (hexadecimalCheck.Checked)
                        {
                            int number = int.Parse(convertingNumTxt);
                            string hex = number.ToString("x");
                            MessageBox.Show("Conversion to hexadecimal was sucessful. Your code is: " + hex, "Hex Conversion Sucessful", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        }
                        else
                        {
                            if (convertNumTxt.Text == null || convertNumTxt.Text == "")
                            {//

                                MessageBox.Show("ERROR: Type - DATA; The conversion box must contain a number or numerical character before the conversion process can begin.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                return;

                            }

                                int decimalNumber;

                                bool blnresult = Int32.TryParse(convertingNumTxt, out decimalNumber);
                                if (!blnresult)
                                {
                                MessageBox.Show("ERROR: Type - SYNTX; The number to be converted may not contain any type of letter or alphabetical character.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                                }
                            else
                            {

                                int remainder;
                                string result = string.Empty;
                                while (decimalNumber > 0)
                            {
                                remainder = decimalNumber % 2;
                                decimalNumber /= 2;
                                result = remainder.ToString() + result;
                            }
                            MessageBox.Show("Conversion was sucessful. Your binary code is: " + result, "Conversion Sucessful");
                            }
                        }
                    }
                }
            }
        }

        private void linkLabel1_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
            ABC_Usage frm = new ABC_Usage();
            frm.Show();
        }
    }
}

Any Help towards this project will be greatly appreciated! Thanks for any help you guys can provide. :)

-Whutchison

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Whutchison