PHP implements code that separates large numbers with , as a delimiter

//Floating point type is not considered
/*
 * method 1
 * echo number_format($str,2,'.',',');
 */
 /* method2
 * First reverse the string strrev and then str_split($str,3);

 $str = strrev($str);
 $arr = str_split($str,3);//987
 $res = '';
 $count = count($arr);
 while($count--){
 $res .= strrev($arr[$count]).',';
 }
 $res = rtrim($res,' ,');
 */
 /* method 3
 * Cut out every 3 characters
 * $count = strlen($str);
 $i = 0;
 $md = $count % 3;
 switch ($ md){
 case 0:
 break;
 case 1:
 $res = $str{0}.',';
 $count -=1;
 $i = 1;
 break;
 case 2:
 $ res = substr($str,0,2).',';
 $count -= 2;
 $i = 2;
 break;
 }
 for(;$i<$count-3;$i+=3 ){
 $res .= substr($str,$i,3).',';
 }
 $res .= substr($str,$i,3);
 */
 /* method 4
 * Regular way to find uncertain length
 $md = strlen($str) % 3;
 $res = substr($str, 0,$md).($md == 0?'':',');
 $res .= preg_replace('(d{3})', '\0,', substr($str, $md));
 $res = rtrim($res,',');
 */
 ?>