First timer PHP edit to update html, some errors - php

Question

this is my first time using PHP in a real project environment. The project is pretty simple, take an existing, working PHP site and update the HTML to be consistent with HTML5. After designing the HTML, I am inserting the PHP from the previous site. This works most of the time, but I get a few errors. For instance:
<?
$sec = $_GET['sec'];
if ($sec == "1") {
echo ('Success!');
}
?>
Is causing the error:
Notice: Undefined index: sec in /file_that_holds_site_build.
Of course that is only if the url doesn't include the append tag (=1) that alerts the message.
So the question is this, what am I missing that causes the $GET when there is no $sec? How do I eliminate this error on first page load?

Answer 1

You're getting that notice because you're trying to access an array index that doesn't exist in some scenarios. Here's how you should be getting the data out of the request.
$sec = array_key_exists('sec', $_GET) ? $_GET['sec'] : null;

Answer 2

Thanks to everyone who provided possible answers to this question. It was Daniel that came up with the easiest fix. Again, I am just adjusting someone else's code to work, so a universal solve would involve too much of my own writing. To the point, the final code looks like this:
<?
if (isset($_GET["sec"])){
$sec = $_GET['sec'];
if ($sec == "1") {
echo ('Success! Your username and password have been sent via email.');
}}
?>
Notice the added if statement. As I said in a comment to Daniel, SO SIMPLE!
Thanks again for everyone's help. I hope to be likewise of service to you all soon.

Answer 3

Simple just use isset($_GET['sec']) to check for the parameter 'sec' before using it in the php code. That should eliminate the error. This is quite trivial I suppose.

Answer 4

I often simply extract() the wohle $_GET super global and then either get the desired variable or not. As a kind of "declaration" I initialize each expected variable first with false. This way I find it much easier to handle than individually doing a check like if(isset($_GET['element'])) ...
$var1=$var2=$var3=false; // my desired variables
extract($_GET); // everything I get from the form
// or: extract($_REQUEST);
if ($var1) { /* do something with it */ }
Possible security risk:
Of course you should be aware that everybody could simply include their own variable as an argument to he page ...