Capital digit to number format

• Such as ： one hundred and thirty-five Turn into 135

function chinese2number($chNum) {
    
    $numArr = array(
        ' zero ' => '0',
        ' One ' => '1',
        ' Two ' => '2',
        ' 3、 ... and ' => '3',
        ' Four ' => '4',
        ' 5、 ... and ' => '5',
        ' 6、 ... and ' => '6',
        ' 7、 ... and ' => '7',
        ' 8、 ... and ' => '8',
        ' Nine ' => '9',
    );
    $numUnit = array(
        ' Ten ' =>'10',
        ' hundred ' =>'100',
        ' thousand ' =>'1000',
        ' ten thousand ' =>'10000',
        ' Billion ' =>'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;
}