declaring variable in class

Is it okay to declare the variable any part of your class ? I have this code, I am using laravel 5.1 framework

In my controller

 public function myTest(){

     $i = 0;<--- is it okay to declare if we use oop,or we should put on top and declare private.
     foreach($myarray as $arr){
            // do something
             // do something with $i
      }


   }

via Chebli Mohamed