Copy data from one column to another

I have a spreadsheet with a bunch of account numbers in column A many of which are duplicates. In Column C i have the same account numbers only not duplicates. In column D i have passcodes for each of these account numbers.

What i basically want to do is lookup the account numbers in column C and copy the passcode from column D to column B if what's in column A matches up with the passocde on the same row in column C.

This is the formula i'm using in column B where i want the data to be.

=if(A2=C:C,D)

Is there another way to accomplish this? =lookup maybe?