在使用OpenFileDialog后，如何在文本文件的每一行末尾添加逗号？

using System;
using System.IO;

class Program
{
    static void Main()
    {
        OpenFileDialog openFileDialog = new OpenFileDialog();
        openFileDialog.Filter = "文本文件|*.txt";
        openFileDialog.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);

        if (openFileDialog.ShowDialog() == DialogResult.OK)
        {
            string filePath = openFileDialog.FileName;

            try
            {
                string[] lines = File.ReadAllLines(filePath);

                for (int i = 0; i < lines.Length; i++)
                {
                    lines[i] += ",";
                }

                File.WriteAllLines(filePath, lines);
            }
            catch (Exception ex)
            {
                Console.WriteLine("发生错误：" + ex.Message);
            }
        }
    }
}