金额大小写转化、阿拉伯数字转大写数字，大写数字转阿拉伯数字

题：请写个程序，将类似下面的大写金额转化为阿拉伯数字。
大写金额样例：玖仟伍佰零玖亿壹佰零玖万玖仟伍佰壹拾捌元整。

$a = "玖仟伍佰零玖亿壹佰零玖万玖仟伍佰壹拾捌元整";
$s = str_replace(array('壹','贰','叁','肆','伍','陆','柒','捌','玖','零','仟','佰','亿','整','元','拾','万'), array(1,2,3,4,5,6,7,8,9,0,'','','','','','',''), $a);
echo $s;

$str = "玖仟伍佰零玖亿壹佰零玖万玖仟伍佰壹拾捌元整";
$capital = array('壹','贰','叁','肆','伍','陆','柒','捌','玖','零');
$relationship = array('壹' => 1,'贰' => 2,'叁' => 3,'肆' => 4,'伍' => 5,'陆' => 6,'柒' => 7,'捌' => 8,'玖' => 9,'零' => 0);
$letter = '';
for ($i=0; $i<mb_strlen($str); $i++) {
$s = mb_substr($str, $i, 1);
if (in_array($s, $capital)) {
$letter .= $relationship[$s];
}
}
echo $letter;