Undefined index. Server Error or coding problem?

i tried to do some practise about form actions and inputs and copy-paste a piece of codes but i got Undefined index: fname and Undefined index: age. The cod开发者_开发问答es were taken from very popular php tutorial website, there should not be any problem with them but submitting them anyway.Is this server error or something like that?

          <form action="posting.php" method="post">
          Name: <input type="text" name="fname" />
          Age: <input type="text" name="age" />
          <input type="submit" />
          </form>
          <?php

          echo $_POST["fname"];
          echo $_POST["age"];

          ?>

You need to make sure $_POST is getting information before you try to read from it. There are a variety of ways to do this. Here's one:

<form action="posting.php" method="post">
    Name: <input type="text" name="fname" />
    Age: <input type="text" name="age" />
    <input type="submit" />
</form>

<?php
    if(isset($_POST)) {
        echo $_POST["fname"];
        echo $_POST["age"];
    }
?>

Until that form is submitted, $_POST is empty and trying to read anything out of it will result in such a notice.

<?php

if (isset($_POST['fname']) && isset($_POST['age'])) {
    echo $_POST['fname']; 
    echo $_POST['age'];
}