Mhon penjelasan

<?php

function auto_number($field,$table,$key,$Parse,$Digit_Count){
$NOL="0";
$sql = mysql_query("Select $field from $table where $key like '$Parse%' order by $key DESC");
$counter=2;
if(mysql_num_rows($sql)==0)
{
while($counter < $Digit_Count)
{
$NOL="0".$this->NOL;
$counter++;
}
return $Parse.$this->NOL."1";
}
else
{
$R = mysql_fetch_array($sql);
$K = sprintf("%d",substr($R[0],-$Digit_Count));
$K = $K + 1;
$L = $K;
while(strlen($L)!=$Digit_Count)
{
$L = $NOL.$L;
}

return $Parse.$L;
}
}

echo auto_number('nis','mahasiswa','nis',$kdFakultas.$kdJurusan.$thnMasuk,$jmlUrut);

?>