title: PHP using double quotes or single quotes in a function difference
body: <p>Hey I have some simple php/html:</p>
  
  <pre><code>&lt;?php
    if( $_POST["name"] || $_POST["age"] )
    {
       echo "Welcome ". $_POST['name']. "&lt;br /&gt;";
       echo "You are ". $_POST['age']. " years old.";
       exit();
    }
  ?&gt;
  &lt;html&gt;
  &lt;body&gt;
  
  
    &lt;form action="&lt;?php $_PHP_SELF ?&gt;" method="POST"&gt;
    Name: &lt;input type="text" name="name" /&gt;
    Age: &lt;input type="text" name="age" /&gt;
    &lt;input type="submit" /&gt;
    &lt;/form&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>I don't understand why on the second line we use double quotes i.e. <code>$_POST["name"]</code> but in the echo statement we use $_POST['name'], could someone tell me why these are different? Completely new to PHP...</p>