title: php $_POST output error
body: <p>I am trying simple web form action in PHP, whatever input given to in the input field output value is <code>1</code>. and undefined index error for <code>username</code>, <code>password</code> when <code>isset</code> not present before the <code>$_POST</code></p>
  
  <pre><code>&lt;html&gt;
  &lt;form action="&lt;?php echo $_SERVER['PHP_SELF']?&gt;" method="post"&gt;
  &lt;input type="text" name="username"&gt;
  &lt;input type="password" name="password"&gt;
  &lt;input type="submit"&gt;&lt;/form&gt;
  &lt;/html&gt;
  
  &lt;?php
  $usernmae=isset($_POST["username"]);
  $pass=isset($_POST["password"]);
  echo $usernmae," ",$pass;
  ?&gt;
  </code></pre>