public API codeproject?

You can achieve a this without any API. Just use HttpWebRequest and HttpWebResponse. The url to use for searching is this:

http://www.codeproject.com/search.aspx?doctypeid=1&q=C%2b%2b&sort=createddesc&field=tag[^]

By playing around with that search page I found out you can define in which field is being searched. By having the parameter field equal to tag the documents of doctypeid equal to 1 (articles BTW) you search for article by tag. All that is left to do for you now is to parse the response with the HtmlAgilityPack for instance.
Paging is done via the pgsize and pgnum parameters where pgsize denotes how many results are packed into the response and pgnum denotes which page number to return.

Hope this gives you an idea.

Best Regards,

-MRB