If you know a language, especially a high level language such as C++ then there is nothing wrong with getting out and developing some software!
Choose an idea, whether it be something that you or someone else needs, or if it is just for fun. Start of simple, a graphical calculator for example and then work your way up to something like a game.
Write out your algorithms, plan it effectively and design it! The most important part, don't rush into it! Use the knowledge you have, and when you get stuck there is always Daniweb and the official resources for your language of choice.
As AHarrisGsy said - use your knowledge and tools to build something of interest to you. Another approach would be to go to the web site of any number of open source projects and try to solve some of the currently unresolved issues posted on the site. www.apache.org is a good place to go as a start, or explore the projects hosted on sourceforge.net.