Home PHP: "Notice: Undefined variable", "Notice: Undefined index", and "Notice: Undefined offset"
 I am running a PHP script, and keep getting errors like: Notice: Undefined variable: my_variable_name in C:\wamp\www\mypath\index.php on line 10 Notice: Undefined index: my_index C:\wamp\www\mypath\index.php on line 11 Line 10 and 11 looks like this: echo "My variable value is: " . $my_variable_name; echo "My index value is: " .$my_array["my_index"];  What do these errors mean? Why do they appear all of a sudden? I used to use this script for years and I've never had any problem. What do I need to do to fix them? This is a General Reference question for people to link to as duplicate, instead of having to explain the issue over and over again. I feel this is necessary because most real-world answers on this issue are very specific. Related Meta discussion: What can be done about repetitive questions? Do “reference questions” make sense?