Condition IF in Crystal Reports

Alright so it's a simple question this time!

I've got two fields coming from the db > qty ordered and qty delivered.

If my customer order their items through us but the supplier delivers their goods the invoice will show as qty delivered = 0.

Now I want to put a filter in that if the qty delivered is 0 set it to be = to the qty ordered.

Now things get a bit confusing.. two different types or order use the same template, the orders that go through supplier and orders that I handle both having a particular type...

So this is what I'm trying to do....

IF ORDER.TYPE = 'SOI' THEN ORDERQ.DLVQTY = ORDERQ.QTY

I'm putting this on the formula of the field but nothing changes on the report?!

Any ideas? Does it make sense?!

I'm confused...