I'm just practicing some basic stuff but i don't know why i keep getting this error:

Notice: Undefined index: action in C:\wamp\www\phpvt\lesson09\simpleform.php on line 14


This is my form:

PHP Code:
<?php
        
if($_GET['action'] == 'submit')    {
            echo((
$_GET['txtUsername']));
        }
    
?>
Code HTML4Strict:
<form action="simpleform.php" method="get">
 
		<fieldset>
			<legend>Login Information</legend>
			Username: <input type="text" name="txtUsername" maxlength="20" size="20" /><br />
			Password: <input type="password" name="pwdPassword" maxlength="20" size="20" /><br />
			<input type="submit" name="action" value="submit" />		
		</fieldset>
 
	</form>

Both the php code and the xhtml form code above are in the same file called simpleform.php

I really don't know why i'm getting this error.

Any thoughts?

Thank you.