If then else syntax problem?

[dws]

I have a button to calculate trip information. I can't get the message box to pop up in the following code. Can anyone tell me why?
If [odometer end] and [odometer start] are null and I click the calculate button nothing happens, I want the message box to appear.

here is the code I am using:

If [odometer_start] = Null And [length_of_trip] = Null Then
MsgBox "Note: Two of the Three values are needed to calculate the mileage.", vbExclamation
Else
[odometer_end] = [odometer_start] + [length_of_trip]
End If

The else portion works as I would expect.
Thanks for your help

 

[KjWhal]

I have a button to calculate trip information. I can't get the message box to pop up in the following code. Can anyone tell me why?
If [odometer end] and [odometer start] are null and I click the calculate button nothing happens, I want the message box to appear.

here is the code I am using:

If [odometer_start] = Null And [length_of_trip] = Null Then
MsgBox "Note: Two of the Three values are needed to calculate the mileage.", vbExclamation
Else
[odometer_end] = [odometer_start] + [length_of_trip]
End If

The else portion works as I would expect.
Thanks for your help

If odometer_start and length_of_trip are (I'm assuming)textboxes wouldn't they be blank ("") and not null if they are empty?

If you step through the code when they are blank what are the values?

 

[boblarson]

If IsNull([odometer_start]) And IsNull([length_of_trip]) Then

Or as stated in the previous post, you can check
If (IsNull([odometer_start]) OR [odometer_start]="") And (IsNull([length_of_trip]) OR [length_of_trip]="")

Also, remember this will give the message ONLY if both are null. If you want the message if either one is null then you would need to use OR between them.

 

[dws]

Thanks! I got it to work by changing the syntax to
If IsNull([odometer_start]) And IsNull([length_of_trip]) Then
as Bob suggested. Why is that? The odometer_start and length of trip returned null values when I stepped thru the code they are numeric fields.
Thanks again for your help!

 

[namliam]

a null value is NEVER equal to anything, even Null. therefor your check simply is invalid.

Using the Isnull() function is the proper way to do it.

In SQL you have a simular issue where you do not use "= Null" but "Is Null" to get around the Null.