IIF vs. If...Then...Else in
VB, VBA, and VB .NET
Provided by: Molly Pell, Technical
Project Manager
Visual
Basic, VBA, and Visual Basic .NET support the IIF function as an alternative
to the If...Then...Else statement. Although this may seem like a shortcut,
IIF functions differently than If...Then...Else.
IIF must
evaluate the entire statement when preparing the argument, which can lead to
undesirable side effects. Consider the following code:
VBA and
Visual Basic:
Public Function
Divide(ByVal n1 As Integer, n2 As Integer) As Variant
Divide = IIf(n2 = 0, MsgBox("Cannot divide by 0"), MsgBox(n1 / n2))
End Function
VB.NET:
Public Function
Divide(ByVal n1 As Integer, n2 As Integer) As Object
Return IIf(n2 = 0, MsgBox("Cannot divide by 0"), MsgBox(n1 / n2))
End Function
The intention
of this code is to check whether the divisor is 0. If it is not 0, then we
want to perform the division. If it is 0, then we want to tell the user that
it cannot divide by 0.
When this
function is run, however, both the True and the False expressions are
executed. Regardless of the values passed, the code first shows the "Cannot
divide by 0" message, and then shows a message box displaying the result. Or
even worse, if the divisor is 0, the code breaks with an unhandled
exception.
Resolution
Consider replacing the IIF statement with If...Then...Else. For instance,
you could change the example above to:
VBA and
Visual Basic:
Public Function
Divide(ByVal n1 As Integer, n2 As Integer) As Variant
If n2 = 0 Then
MsgBox ("Cannot divide by 0")
Else
MsgBox (n1 / n2)
End If
End Function
VB.NET:
Public Function
Divide(ByVal n1 As Integer, n2 As Integer) As Object
If n2 = 0 Then
MsgBox("Cannot divide by 0")
Else
MsgBox (n1 / n2)
End If
End Function
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