php help

when to use curly braces {}, Parentheses ( )  and Square brackets [ ] on php <latest>?



im so confuesd when to use curly braces {}, Parentheses ( )  and Square brackets [ ] on php


here i wrote a simple script


 <?
 for ($i = 0; $i < 10; $i++)
        {

        echo "Loop  #$i <br>";
        }
 ?>




now if we change the {} to ()




            http://pastebin.com/SXAtUmkf

as you can see now it wont work



test here http://www.compileonline.com/execute_php_online.php ( the last and first code)