if .. else doubt

why is this work

Code:

---

      If !a <> "" Then
          tempname = !a
        Else
            tempname = !b
        End If

---

but not this???

Code:

---

      If !a = "" Then
          tempname = !b
        Else
            tempname = !a
        End If

---

--this return NULL error

Just a bit programming concept... thanks for explaining... ;)

I can't make any of the two codes to work. I get an Unqualified Reference ...' error at the exclamation mark.

What are you trying to test, anyway? And is it in VB?

.

The exclamation mark is usually used as the logical NOT operator, and would be used for boolean values ; not strings.

The logical not operator in VB is 'Not'.
Eg.

Code:

---

    Dim a As String
    If (Not (a = "")) Then
        MsgBox "A is not empty"
    End If

---

You would appear to also be using the not operator with strings, which you obviously cant do.

- jamie

I should be more specific...


--this code is part of my vb code

--the ! used here is the variable in form, in my case, it's a Textbox's variable


I was trying to check if "a" is an empty string,
if yes, I'll use text in "b" as my data
if no, I'll use text in "a"


Thanks

:)

Code:

---

Dim TempData as string

If IsNull(text1.text) then
  TempData = b
Else
  TempData = a
End If

---

Take a look at the ISNULL() function ;)

Also, I think VB treats "" and Null differently.

(I also think that I posted this very reply just a short while back and it just disappeared.)

.

Thanks everyone..


I just came back from good friday.. today shold be easter holiday but Singapore only declare good friday as holiday... sad sad have to work.. :D

I'll try every suggestion..

again.. Thanks......!!!!!

Simple....
you can't assign a Null value to a variable....
in the first one you can't never assign a null value, 'cause !a got a value.
in the second one Null is not equal to "". so it goes to the else part. Being a variable trying to assign a NULL value, BOOM! error.

finally I underestand.. :)

but...

Do you mean that this code

Code:

---

If !a <> "" Then
          tempname = !a
        Else
            tempname = !b
        End If

---

will always go to the ELSE part??

Thanks

Quote:

---

you can't assign a Null value to a variable....

---

- Rix

yes u can!

var1 = vbNullChar

to avoid maximum confusion, test if !a = vbnullchar, and if it is, then assign it ""

then use it in the test case u posted!

remember that you can have !a with values of any string e.g. "Elvira", zero-lenght string, e.g. "" or a NULL value. You have to consider the fact that any of the 3 can change your operation.
If you test if !a="", then you know !a = "", but if !a="" it's false, it can be 'cause !a = NULL or !a = "Elvira"

TheSarlacc....
with function you can make wonders....

I actually use

Code:

---

if IsNull(!a) then
...

---

is this the only way to check if !a is null?


Other suggestions like

!a = "" and !a = vbNullChar

is to assign null to !a, correct?

:confused:


Thanks!

Don't assign a Null value.
If you want something like it, assign a "" (zero-lenght string ), in the future, you'll see why.
and yes ISNULL() is your only bet. (assuming that is not a zero-lenght string or a normal string, either case you can test that !a is neither, so, by elimination, it got to be NULL.)

Thanks..

I'll keep everything in mind...

;)