1. Find your coding file.
2. Highlight it.
3. Press F2.
4. Delete the part that says .txt and replace it with .cs.
4. Say yes at the prompt.
5. ???
6. Profit.
Or in Notepad, when you first Save As the file, change the drop down box from "Text files *.txt" to "All file types *.*" and save with .cs at the end.