* VB-CODE (2)
Tip 128: Calculating the Beginning and Ending Date of a Month

July 1, 1995

Abstract
When developing an application in Microsoft=AE Visual Basic=AE, you may =
need to
calculate the specific date of the first and last days of a month. This =
article
explains how to accomplish this task in Visual Basic.

Manipulating Dates in Visual Basic
Microsoft=AE Visual Basic=AE offers many functions that you can use to =
determine what
day a specific date falls on, what month it is, and so on. You can use =
the
DateValue function to convert a date string, such as July 3, 1995, to a =
date
serial number. This function usually determines what day of the week a =
specific
date falls on.

The DateSerial function converts a numeric value to a date serial =
number. The
serial number is a unique number that represents each possible date from =
January
1, 100 A.D. through December 31, 9999. Therefore, you can easily =
calculate how
many days elapsed between two specific dates by using the DateSerial =
function.
In the example program below, you want to find the first and last dates =
in the
month of July, 1995. To do this, you convert the string date (July 3, =
1995) to a
date serial number. Then you use the DateSerial function in conjunction =
with the
Year and Month functions to calculate the first date in the month of =
July. You
repeat this routine to determine the last date in the month of July.

After calling the DateSerial function, you must use the Visual Basic =
Year, Month,
and Day functions to extract and decode specific portions of information =
from the
date serial number. You must do this because the date serial number is =
encoded in
a special format.
In the example program below, you use the Year and Month functions to =
determine
which date is the first day of the month. The Month function returns a =
value of
1 through 12 that represents the specified month. In a similar fashion, =
the Visual
Basic Year function returns the year from the encoded serial number.

The MonthEnd function in the example program actually calculates the =
next month's
first day. It then backtracks by one day to calculate the correct date =
for the
last day of the month.

Example Program
This program shows how to retrieve the first and last date for a =
 list, the focus does not automatically
change to the next available item in the list. The example program below =
shows how
to do this.
The ListIndex property of a List Box control tells you which item was =
selected by
the user. Knowing this value, you can use the RemoveItem method to =
delete that
specific entry from the list. For example, if you select the third item =
in the
List Box control, the ListIndex property would be set to a value of two =
(the List
Box control starts numbering the entries from zero).

It is a simple matter, then, to set the focus to the next available item =
in the
list by keeping track of your position within the list. After deleting =
the
selected item, you set the ListIndex property to your current position =
minus one.
You can then set the focus to this newly selected item.

Example Program
This program shows how to delete an item from a List Box control and set =
the focus
to the next available item in the list.

 1. Create a new project in Visual Basic. Form1 is created by default.
 2. Add the following code to the Form_Load event for Form1:

Private Sub Form_Load()
    List1.AddItem "Item #1"
    List1.AddItem "Item #2"
    List1.AddItem "Item #3"
    List1.AddItem "Item #4"
    List1.AddItem "Item #5"
End Sub

 3. Add a List Box control to Form1. List1 is created by default.
 4. Add a Command Button control to Form1. Command1 is created by =
default.
 5. Add the following code to the Click event for Command1:

Private Sub Command1_Click()
    Dim PositionInList As Integer
    Dim NumberOfItemsInList As Integer
    PositionInList =3D List1.ListIndex
    NumberOfItemsInList =3D List1.ListCount
    If NumberOfItemsInList > 0 Then
        If PositionInList >=3D 0 Then
            List1.RemoveItem PositionInList
        Else
            MsgBox "You must select an item to delete.", 48, "Error"
        End If
    Else
        MsgBox "There are no items to delete.", 48, "Error"
    End If
    NumberOfItemsInList =3D List1.ListCount
    If NumberOfItemsInList > 0 Then
        If PositionInList =3D NumberOfItemsInList Then
            List1.ListIndex =3D NumberOfItemsInList - 1
        Else
            List1.ListIndex =3D PositionInList
        End If
    End If
    List1.SetFocus
End Sub

Run the example program by pressing F5. Five items will appear in the =
List Box
control. Notice that no items are selected. Click the Delete command =
button. A
message box is displayed, indicating that you must select an item before =
you can
delete it.
Click the OK command button. Click the third item (Item #3) to select =
it. The
item is deleted from the List Box control, and the focus is moved to the =
next
available item in the list.
Notice that if you attempt to delete an item that does not exist in the =
List Box
control, a message box will be displayed, telling you that there are no =
items to
delete.

Additional References
Tip 24: Avoiding Errors When Removing Items from a List Box