Go to the command window and type these lines, and take a look at what they give back:

? "A" = "ABC"
? "ABC" = "A"
? "" = "A"
? "A" = ""
? "" == "A"
? "A" == ""

I think that will get you on the right track!

>I have a form to let users change the details of an order (for example to add or delete product quantity). I have txtBoxes for Product and Qty (the ControlSources are mProduct and mQty, respectively). In the Valid of each txtBox, I call a method I have created called CalcQty (ThisForm.CalcQty(.T.)). So, once the user has entered both the Product number and the Qty, the program is to then do a calculation and update some other txtBoxes that I also have on this same form -- txtBoxes for Original Qty and Adjusted Qty.
>
>Here is the CalcQty Method:
>
>

>LPARAMETERS plCalc
>
>IF plCalc = .T.
>
>	* IF Product or Qty hasn't been input, can't do calculations!
>	IF mProduct = ""
>		RETURN
>	ENDIF
>
>	IF mQty = 0
>		RETURN
>	ENDIF
>
>	DO CASE
>		* CASE Add Product
>		CASE blah,blah,blah
>
>		* CASE Delete Product
>		CASE blah,blah,blah
>	ENDCASE
>
>	ThisForm.Refresh()
>
>ENDIF
>

>
>The problem is that IF mProduct = "" doesn't seem to be working. When mProduct equals = "" then you are indeed RETURNed. But when mProduct = something different, like "281600", you are also RETURNed. I have looked at it running the Debugger. For example, when the Debugger says that mProduct = "281600" the IF mProduct = "" statement seems to evaluate to True (even though it should evaluate to False), and you are RETURNed. So the calculations *NEVER* get done. So frustrating! The IF mQty statement seems to be evaluating without a problem.
>
>Why the difference? Any help would be most appreciated. TIA, Chuck Henry.