How to auto-populate the app version number in plist? (iPhone/iPad)

I have a plist that I want to auto-populate the version number of the app in. Is this possible? If so please can someone tell me how?

Solution

i think this is the best answer: http://blog.jayway.com/2011/05/31/auto-incrementing-build-numbers-in-xcode/ it use PlistBuddy to create a plist at every build and increment build number. I followed this way in a my project.