Difference between sub and function in QTP

Sub and Functions are used to write a common code that can be called many times in a programm in QTP.

Difference between Sub and Function is that We can return a value from a function but In sub it is not possible to return value.

Example - 

Sub mysub(b)

 a= 8*b
 print a

End Sub


Public Function RandomCharacters(CharLength)
   str = ""
   intHighNumber = 90
   intLowNumber = 65
    Randomize
    For i = 1 to CharLength
        RdNumber = Int((intHighNumber - intLowNumber + 1) * Rnd + intLowNumber)
        stch = chr(RdNumber)
        str =   str&stch
    Next
    Reporter.ReportEvent micPass,"Random Character Generated","Random Character "&str&" was generated"
    RandomCharacters = str   'return a value from function
End Function