Application.MajorVersion
From Xojo Documentation
Read-Only Property (As Integer )
The major version of the Application, corresponding to the version information. The range is from 0 to 255. This can only be set in the IDE, but you can read the value in your code.
Notes
Typically version numbers are written as 1.2.3.4 (MajorVersion.MinorVersion.BugVersion.NonReleaseVersion).
Sample Code
Puts all the individual versions together to create the full version: