How to check if any `.txt` file exists in a folder? 

If the folder still have `.txt` file output a error messagebox.

Thx all! Actually i want to make a function can check any .txt file exists in a folder. If yes write a error message to eventLog.
Final My code:

```
     System.Diagnostics.EventLog appLog = new System.Diagnostics.EventLog();
     DirectoryInfo di = new DirectoryInfo(@"c:/Users/Public/Definitions");
     FileInfo[] TXTFiles = di.GetFiles("*.txt");
     foreach (var fi in TXTFiles)
     {
         if (fi.Exists)
         {
             appLog.Source = "Definitions Folder still have text files";
             appLog.WriteEntry("Still have txt files.");
         }
     }  

```