The index of the string chosen (use after calling DoModal). Strings are numbered starting at 0 in the order that they were added, not the order that they appear in the dialog.
[Visual Basic .NET] Public ReadOnly Property Choice As Integer
[C#] public int Choice {get;}
Product Availability
Available with ArcGIS Desktop.
Remarks
The Choice property returns the index of the selected item in the list. The items are numbered starting at 0 in the order that they were added, not the order that they appear in the dialog.