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Recognizing U.S. ZIP Codes
Matching U.S. ZIP codes for syntactic correctness is straightforward. They are composed from a string of numeric characters. Any nonnumeric character is an error, except for the dashes in ZIP+4 codes.
To match the standard 5-digit ZIP code we could use this regular expression:
[0-9]{5}
The “+4” part of the extended ZIP code is a variation with a “4” in the braces. Combined, we get this for the whole ZIP+4 combination with its embedded dash:
[0-9]{5}\-[0-9]{4}
This will also match a ZIP code with too many digits in either half. We need to delimit the ZIP code and allow either of the two forms. In this case, we ...
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