USA’s Zip Code Validation in PHP

My friend Sushil was trying to write the regular expression for validating the format of the zip code of USA. After spending few minutes, I came to this solution.

The valid format of zip code of USA might be a five digit number like “12345” or in the format of 4 digit followed by first 5 digits like “12345-5434“.And, we need a function to validate the both kind of format of zip code.

Here is the function,

function validateUSAZip($zip_code)
{
  if(preg_match("/^([0-9]{5})(-[0-9]{4})?$/i",$zip_code))
    return true;
  else
    return false;
}

Now, let’s look at the explanation of the regular expression used in this function. A perl regular expression always starts with “/” and ends with “/” and “i” after closing “/” refers that the expression is “case insensitive”.As you know, “^” refers that, it is the beginning of the expression. And, the expression “([0-9]{5})” tells that there should be exactly 5 digits at the beginning of the expression. Furthermore, the second expression “(-[0-9]{4})“, means that after first 5 digit there should be another 4 digit followed by the “-” sign.The “?” sign next to second expression tells that the second expression is optional.And finally, the “$” sign before “/i” refers that it is the end of the expression.

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