Format cell so number entered will show only one way

[Frustrated in AZ]

I have a speadsheet I am working on and would like some cells to be
"formatted" so when the user enters a number it will only accept it one way.
For example:
If the user enters the case number as 081234, the cell is currently
formatted to accept it as 08-1234 (I set this up under
Format>Cells>Number>Custom, which works). However, if the user enters the
case number WITH the hyphen I would like to use the Data>Validation feature
so an error alert pops up letting them know that no hyphen is needed. I was
able to set this up, but if I enter the case with OR without the hyphen I get
an error message for both, instead of just when using the hyphen. I see
there is also a space to enter a formula under Data>Validation but,
unfortunately, I do not understand formulas very well. Can somebody please
help? Thank you!

 

[T. Valko]

Try this:

Data>Validation>Allow>Custom

Formula: =ISERROR(FIND("-",A1))

 

[T. Valko]

You said that the cell is *custom formatted* to *display* a dash. While the
dash is *displayed* it is not part of the true underlying value of the cell.
Using data validation prevents a user from actually entering a dash in the
cell.

If you use data validation and enter a "-" in the cell you'll get the error
message. If you enter something without a "-" nothing will happen, no error
message.