var undefined getting value $ _GET ['page'] - php

Question

I want paging is a content of a news blog. Everything works correctly, the page content is successful. But I get an error screen displays PHP:
Notice: Undefined index: page in C:\wamp\www\index.php on line 146
code with the line that gives the error:
$maxreg = 1;
$pag = $_GET['page'];
if (!isset($pag) || empty($pag)){
$min = 0;
$pag = 1;
}else{
if($pag == 1){
$min = 0;
}else{
$min = $maxreg * $pag;
$min = $min - $maxreg;
}
}
include("js/class.AutoPagination.php");
$obj = new AutoPagination(contar_contenido(), $pag);
mostrar_contenido($min,$maxreg);
echo $obj->_paginateDetails();
The line gives the error is this:
$ page = $ _GET ['page'];
The first page by default index.php and contains no var in the url.
I do not understand why if fails below by a conditional var I determine if that has content or not.
Should not show any error php, could someone give me a solution? Thanks

Answer 1

You don't need to do
$pag = $_GET['page'];
Check if $_GET['page'] is set first:
if(!isset($_GET['page']) || empty($_GET['page'])) {
$min = 0;
$pag = 1;
}else{
if($pag == 1){
$min = 0;
}else{
$min = $maxreg * $pag;
$min = $min - $maxreg;
}
}

Answer 2

I quote;
Declare your variables. Or use isset() to check if they are declared before referencing them;
PHP: "Notice: Undefined variable", "Notice: Undefined index", and "Notice: Undefined offset"

Answer 3

I found the solution, I've built so, assigning a value to the variable empty get in if it is indefinite.
Maybe it's a very elegant solution, but it works perfect paging.
if(!isset($_GET['page']) || empty($_GET['page'])) {
$_GET['page']="";
}
$maxreg = 2;
$min = 0;
$pag = $_GET['page'];
I think the second conditional left over.
I leave it here in case anyone has the same problem. This way you can fix it.