A lot of people don't actually post code that compiles or have them in it. You could have a "does this look like C?" algorithm. Similar to what Google Translate uses to auto-detect languages.
I wasn't suggesting a "catch-all" type of approach. Just a simple "does the string: 'void setup()' exist and '[
code]' does not"? If true, print a simple message and then allow the next post to go through. Again, similar to what happens when someone posts while you edit/create a post.
And I agree about the [code] button. (Special trick to make that appear). I made the (empty) gap after the "[" but before the word "code" to be in bold.
Finally! I could not figure out how you did it.