How to convert uppercase numbers to Arabic numerals in php

function chinese2number($chNum) {
    $numArr = array(
        '零' => '0',
        '一' => '1',
        '二' => '2',
        '三' => '3',
        '四' => '4',
        '五' => '5',
        '六' => '6',
        '七' => '7',
        '八' => '8',
        '九' => '9',
    );
    $numUnit = array(
        '十' =>'10',
        '百' =>'100',
        '千' =>'1000',
        '万' =>'10000',
        '亿' =>'100000000',
    );
    $number = 0;
    for ($i = 0;$i<=mb_strlen($chNum); $i++) {
        $str = mb_substr($chNum,$i,2);
        $first = mb_substr($str,0,1);
        $second = mb_substr($str,1,1);
        if (isset($numUnit[$first])){
            if (!$number) {
                $number = 1;
            }
            $number *= $numUnit[$first];
        } else if (isset($numArr[$first])) {
            $i++;
            if (isset($numArr[$second])) {
                if ($numArr[$first] == 0) {
                    $i--;
                }else{
                    $number += intval($numArr[$first].$numArr[$second]);
                }
            } else if(isset($numUnit[$second])) {
                $number += intval($numArr[$first]*$numUnit[$second]);
            } else{
                $number += intval($numArr[$first]);
            }
        }

    }
    return $number;
}