Assuming that your Zip1 (eg.: 12345) is numeric, and Zip2 (eg.:54321-1234) is a character field because of the separating hyphen, you could build a Zip numeric field as follows:
If Zip1 is already a character field, then it's a little shorter:
I don't think the offered suggestion will work. Both fields are numeric. Neither field contains the "-" zip seperator.
I'm trying real hard to avoid making the numeric fields into character fields. If I did, I could use the prior suggestion, but I'm still missing the "-" which seems key in parsing the field as suggested.