regular expression validator for a text box to accept a blank value or a single charecter 'C'

Question

what would be the regular expression for a regular expression validator if a text box in my web page can only accept a blank value or charecter 'C'

Thanks

Answer 1

It would be this:

^C$

That indicates that only a single C character will be accepted. Leaving the field empty will also be acceptable, because RegEx validators do not flag empty fields as incorrect.