property CalendarCombo.DoDate (Year as Long, Month as Long, Day as Long) as Date
Composes a DATE type, based on year, month and day.

TypeDescription
Year as Long A long expression that indicates the year.
Month as Long A long expression that indicates the month. 1 - January, 2 - February, ... 12 - December
Day as Long A long expression that indicates the day number. 1 - First day of the month, ... If the Day is -1, the DoDate returns the last day of the specified month/year.
Date A DATE expression that indicates the built date

Use the DoDate to build a DATE expression given  the year, month and the day. If the Day is -1, the DoDate returns the last day of the specified month/year.