Please use the new "Open" command in Textastic 5.2. It allows you to open a file from Working Copy and edit it. 

Please have a look at this Apple support article: http://support.apple.com/en-us/HT201377

If you buy the latest version in iTunes on your Mac or PC, you should be able to download the latest compatible version from the "Purchased" section in the App Store on your iPad.

It looks very similar to C. You could try to manually select the C syntax definition. Maybe it is better than nothing.

The latest version of Textastic (5.2) is updated for the higher resolution of the iPhone 6 and iPhone 6 Plus.

You can create a new file locally and then upload it to Dropbox using the file transfer screen (globe icon). 

For more info, have a look at this entry in the Trxtastic for iPhone manual: http://www.textasticapp.com/iphone/v5/manual/lessons/How_can_I_download_or_upload_files.html

Do you have a link with more information?

I plan to submit it to Apple this week.