title: PHP radio button - undefined index
body: <p>Simple question, when I didn't select any radio button, I got error message
  Undefined index: gender</p>
  
  <pre><code>&lt;?PHP
  if(isset($_POST['register'])){
  
      $gender=$_POST['gender'];
      echo $gender;
      }
  ?&gt;
  
  &lt;html&gt;
      &lt;form action="testing.php" method="POST"&gt;
          &lt;input type="radio" name="gender" value="male" /&gt;Male
          &lt;input type="radio" name="gender" value="female" /&gt;Female
      &lt;input type="submit" name="register" value="Register" /&gt;
      &lt;/form&gt;
  &lt;/html&gt;
  </code></pre>