Making a text field required only if another text field has been filled out in C# : <p>I'm making a web form to enter customer information into a database.  I have 4 textboxes for billingAddress, billingCity, billingState, and billingZip. BillingAddress is an optional field.</p>

<p>My question is: how can I set up requiredfieldvalidators on billingCity, billingState, and billingZip so that these fields are only required if billingAddress has been filled out?</p>

<p>*Side Note: Database requirements have separate columnms for address, city, state, and zip code, so I can't just combine them into one field.</p>
