解决发票系统中，发票单上需要填写中文金额的问题：

functionToChineseNum($num){$zh_num=['零','壹','贰','叁','肆','伍','陆','柒','捌','玖'];$zh_unit=['分','角','元','拾','佰','仟','万','拾','佰','仟','亿','拾','佰','仟'];if(!is_numeric(str_replace(',','',$num))){return$num;}$number=strrev(round(str_replace(',','',$num),2)*100);$length=strlen($number);$ch_str='';for($length;$length>0;$length--){$index=$length-1;if($number[$index]=='0'&&!in_array($zh_unit[$index],['万','元','亿'])){$ch_str.=$zh_num[$number[$index]];}elseif($number[$index]=='0'&&in_array($zh_unit[$index],['万','元','亿'])){$ch_str.=$zh_unit[$index];}else{$ch_str.=$zh_num[$number[$index]].$zh_unit[$index];}}$format_str=trim(preg_replace(['/零{2,}/u','/零万/','/零元/','/零亿/'],['零','万','元','亿'],$ch_str),'零');if(preg_match('/(分|角)/',$format_str)===0){$format_str.='整';}return$format_str;}