Android Application has two properties named versionName and versionCode in its AndroidManifest.xml file.
Both specify the version of the application. versionName is what the user sees and can be any String.
versionCode must be an integer. The Android Market(Google Play) determine the version of the application based on the versionCode. The update of an existing application is checked by the versionCode. The versionCode should be start with “1” and increase this value by one, if you roll-out a new version of your application. When ever a change in the versionCode the Play Store will notify the user about the update.