First thing first:
This is a copy from the original at support wordpress.
Because WordPress.com doesn’t allow us to use code on our blog, with consideration those code might be potentially dangerous. However, there is a way to post source code for viewing. By using a shortcode have been created by them, we can wrap around source code that preserves its formatting and even provides syntax highlighting for certain languages, like so:
To accomplish the above, just wrap your code in these tags:
your code here
Its easy right?