PHPを使用して漢字と数字を一致させる方法

function getChinese($string,$encode="GBK") {
  switch($encode){
   case "GBK" :$codelength=2;break;
   case "GB2312" :$codelength=3;break;
   case "UTF-8" :$codelength=3;break;
   case "UTF-16" :$codelength=4;break;
  }
  $tmpstr = '';
  $arr = array(1,2,3,4,5,6,7,8,9,0);
  $strlen = strlen($string);
  for($i=0; $i<$strlen; $i++) {
   $str=substr($string, $i, 1);
   $str1=trim($str);
   if( ord($str)>0xA0 ){
   $tmpstr.= substr($string, $i, $codelength);
   $i = $i+$codelength-1;
   }
  }
 return $tmpstr;
}