<?php
$str ="(10*2)/(3*40)*100";
$str = str_split($str); // make str an array
$arr = array();
$j=0; // counter for new array
for($i=0;$i<count($str);$i++){
if(is_numeric($str[$i])){ // if the item is a number
$arr[$j] = $str[$i]; // add it to new array
$k = $i+1;
while(is_numeric($str[$k])){ // while it's still a number append to new array item.
$arr[$j] .= $str[$k];
$k++; // add one to counter.
if($k == count($str)) break; // if counter is out of bounds, break loop.
}
$j++; // we are done with this item, add one to counter.
$i=$k-1; // set new value to $i
}else{
// not number, add it to the new array and add one to array counter.
$arr[$j] = $str[$i];
$j++;
}
}
var_dump($arr);