How to convert a Roman numeral to integer in PHP?

How about this:

$romans = array(    'M' => 1000,    'CM' => 900,    'D' => 500,    'CD' => 400,    'C' => 100,    'XC' => 90,    'L' => 50,    'XL' => 40,    'X' => 10,    'IX' => 9,    'V' => 5,    'IV' => 4,    'I' => 1,);$roman = 'MMMCMXCIX';$result = 0;foreach ($romans as $key => $value) {    while (strpos($roman, $key) === 0) {        $result += $value;        $roman = substr($roman, strlen($key));    }}echo $result;

which should output 3999 for the supplied $roman. It seems to work for my limited testing:

MCMXC = 1990MM = 2000MMXI = 2011MCMLXXV = 1975

You might want to do some validation first as well :-)

I am not sure whether you've got ZF or not, but in case you (or any of you who's reading this) do here is my snippet:

$number = new Zend_Measure_Number('MCMLXXV', Zend_Measure_Number::ROMAN);$number->convertTo (Zend_Measure_Number::DECIMAL);echo $number->getValue();

• Zend_Measure_Number on framework.zend.com

This is the one I came up with, I added the validity check as well.

class RomanNumber {    //array of roman values    public static $roman_values=array(        'I' => 1, 'V' => 5,         'X' => 10, 'L' => 50,        'C' => 100, 'D' => 500,        'M' => 1000,    );    //values that should evaluate as 0    public static $roman_zero=array('N', 'nulla');    //Regex - checking for valid Roman numerals    public static $roman_regex='/^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$/';    //Roman numeral validation function - is the string a valid Roman Number?    static function IsRomanNumber($roman) {         return preg_match(self::$roman_regex, $roman) > 0;    }    //Conversion: Roman Numeral to Integer    static function Roman2Int ($roman) {        //checking for zero values        if (in_array($roman, self::$roman_zero)) {            return 0;        }        //validating string        if (!self::IsRomanNumber($roman)) {            return false;        }        $values=self::$roman_values;        $result = 0;        //iterating through characters LTR        for ($i = 0, $length = strlen($roman); $i < $length; $i++) {            //getting value of current char            $value = $values[$roman[$i]];            //getting value of next char - null if there is no next char            $nextvalue = !isset($roman[$i + 1]) ? null : $values[$roman[$i + 1]];            //adding/subtracting value from result based on $nextvalue            $result += (!is_null($nextvalue) && $nextvalue > $value) ? -$value : $value;        }        return $result;    }}