It'll format it as monospace, and typically in a format that's easier to recognize as being code.

IIRC you can do that by gating code like this:

  '''
  code goes here
  '''

in markdown, but it's been a while.

(The spaces are necessary for HN markup, but not the markdown formatting).

Github has pretty comprehensive documentation on their flavor of markdown used for formatting; Here's a direct link to the section on fenced code blocks: https://github.github.com/gfm/#fenced-code-blocks