diff --git a/php/08_stack/Compute.php b/php/08_stack/Compute.php
index d9b8eb4..5bd2913 100644
--- a/php/08_stack/Compute.php
+++ b/php/08_stack/Compute.php
@@ -13,7 +13,7 @@ function expression($str)
     $operStack[] = NULL;
 
     for ($i = 0; $i < count($arr); $i++){
-        if (ord($arr[$i]) >= 48 && ord($arr[$i] <= 57)){
+        if (ord($arr[$i]) >= 48 && ord($arr[$i]) <= 57){
             array_push($numStack, $arr[$i]);
             continue;
         }
@@ -85,4 +85,4 @@ function compute(&$numStack, &$operStack){
 }
 expression('-1+2-(1+2*3)');
 echo PHP_EOL;
-eval('echo -1+2-(1+2*3);');
\ No newline at end of file
+eval('echo -1+2-(1+2*3);');