[thelist] single quotes and arrays

[Garth Hagerman]

Hi everybody-
Since The List is alive again (hooray!), here's a query.
I've been making the same boo-boo over and over for years. I have a rote mechanical understanding of what to do about it, but I do not understand the conceptual background.

In PHP, I pass info to another page using a form. The page receiving the info has a line like this:
$pageid = $_GET[pageid];

This works, so there doesn't seem to be anything wrong, so I do it over and over and over. But it logs something like this into the error_log:
"PHP Notice:  Use of undefined constant pageid - assumed 'pageid' ". 

Since this happens a lot, the error_log gets to be a very large file.

So, I understand how to stop getting that notice: put single quotes around pageid.
But why? pageid isn't a string, it's the name of an array element. If I do the same single quote thing with other arrays, something like: 
echo("<option value=\"$row['id']\">$row['title']</option>\n");
 it's a fatal error and the whole page explodes.

I've tried to find a reasonable explanation online, but haven't found anything which makes the little "eureka!" light over my head light up.

  Thanks in advance
  Garth
                               

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