how to get custom number of items in the same row at every loop

index.php

<?php
$arr = ['a','b','c','d','f','g'];
$a = 0;
foreach ($arr as $value) {
// 3 it's number of items
  if($a % 3 == 0){
		echo "<br>";
	}
	echo $value;
	$a++;
}

?>