[NuAlpha]

Another update for this module. Better detection of one too many characters in postal codes and additional correction of 'fat-fingering' the dash.

<?php
#########################################
##      ## Validate Zipcode ##         ##
#########################################
## Version: 1.2.6 (3/2/2004)
## Last updated: 6/8/2004

if (!defined('XCART_SESSION_START')) { header("Location: ../"); die("Access Denied!"); }

function validate_zipcode($zipcode,$country='') {
	
	$zipcode = trim($zipcode); // Prep by removing excess spaces.
	
	switch ($country) {
	case 'US': // Validate United States postal codes.
		if (strlen($zipcode) > 5 && strlen($zipcode) <= 10) { // If not length 5, then check for valid format.
			if (preg_match("/^([0-9]{5})([-=._\/\ ])?([0-9]{4})?(.)?/", $zipcode, $checkZip)) {
				if (!empty($checkZip[3])) { // Is it a zip+4 code?
					# Prevent char deletion by concatenation or overflow during next part of validation code. Instead, cause an error.
					if (empty($checkZip[4])) { // This checks if the last digit will be cutoff from an empty $checkZip[2].
						if (empty($checkZip[2]) || $checkZip[2] != '-')
							$checkZip[2] = '-'; // Ensure that a dash is present in 9 digit zip code.
						$zipcode = $checkZip[1].$checkZip[2].$checkZip[3];
					} else // Cause an error because there are 10 digits, instead of 9 with a partitioning character.
						$zipcode = '';
				} else // Cause an error from incorrect length.
					$zipcode = '';
			} else // No valid zip code matched.
				$zipcode = '';
		} elseif (strlen($zipcode) < 5 || preg_match("/[[:alpha:]]/i",$zipcode)) // Check min length or presence of a letter.
			$zipcode = '';
		# If none of the above, do not modify zipcode. It is a valid 5 numeric digits.
		break;
	case 'CA': // Validate Canadian postal codes.
		if (strlen($zipcode) >= 6 && strlen($zipcode) <= 7) { // Check for valid length.
			if (preg_match("/^([A-z0-9]{3})([-._\/\ ])([A-z0-9]{3})(.)?/i", $zipcode, $checkZip)) {
				if (empty($checkZip[4])) {
					if ($checkZip[2] != ' ')
						$checkZip[2] = ' '; // Ensure that a space is between the two code segments.
					$zipcode = $checkZip[1].$checkZip[2].$checkZip[3];
				} else // Cause an error because there are 7 digits, instead of 6 with a partitioning character.
					$zipcode = '';
			} else // Cause an error from incorrect length.
				$zipcode = '';
		} else // No valid zip code matched.
			$zipcode = '';
		
		if (!empty($zipcode))
			$zipcode = strtoupper($zipcode); // Capitalize alphabetic characters for Canadian postal code.
		break;
	}
	
	return $zipcode;
}
?>

Again, let me know if you have problems with this so that I can correct any bugs.