Writing to an output text file and finding out extra characters or lines in it?

If you’re using File.OpenWrite() to create the output file, make sure the output file does not exist.  This MSDN article explains what happens if output file exists:

For an existing file, it does not append the new text to the existing text. Instead, it overwrites the existing characters with the new characters. If you overwrite a longer string (such as “This is a test of the OpenWrite method”) with a shorter string (such as “Second run”), the file will contain a mix of the strings (“Second runtest of the OpenWrite method”).