<?php

   $x = 8;
   $y = -3;
   $a = $x + $y;
   $b = $x += 9;

   echo {$z};  // 5
   echo {$b};  // 17

   $string_1 = "Hello";
   $string_2 = "World!";

   $string_1 .= $string_2;
   $string_3 = $string_1 . "World!"

   echo {string_1};  // Hello World!
   echo {string_3};  // Hello World!

?>