Working with app.config in c#

appconfig_work.cs

//first, let's instantiate the Configuration manager class


Configuration configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);

if (ConfigurationManager.AppSettings.Count == 0)
 {
    configuration.AppSettings.Settings.Add("ffmpegPath", "");
    configuration.Save(ConfigurationSaveMode.Full);
    ConfigurationManager.RefreshSection("appSettings");
}
string key = ConfigurationManager.AppSettings["ffmpegPath"];


   foreach (string key in ConfigurationManager.AppSettings)
                {

                    string value = ConfigurationManager.AppSettings[key];
                    if (value == "")
                    {
                        MessageBox.Show("ffpeg path not configured !");
                        openFileDialog1.Title = "Select ffmpeg executable file";
                        if (openFileDialog1.ShowDialog() == DialogResult.OK)
                        {
                            string ffmpegPath = openFileDialog1.FileName;
                            //Configuration configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
                            //configuration.AppSettings.Settings.Add("ffmpegPath", Path.GetFullPath(ffmpegPath));
                            var settings = configuration.AppSettings.Settings;
                            settings["ffmpegPath"].Value = Path.GetFullPath(ffmpegPath);
                            configuration.Save(ConfigurationSaveMode.Full, true);
                            ConfigurationManager.RefreshSection("appSettings");
                        }
                    }
                    else
                    {
                        MessageBox.Show("ffmpeg path already configured !");
                    }
                }         
            
            

Sorry for code style !