checkbox null value causing error

[beach_nc]

I am having a problem inserting the value from a checkbox into a MySQL table. The checkbox is used as a yes or no answer. When the box is checked it works fine, when it is not checked I get...

Notice: Undefined variable: dnr in c:\inetpub\wwwroot\dev\php\addvisit.php on line 15

If I could either fix the problem so the error message doesn't fix, or suppress the error message so it doesn't print on the screen.

If dnr is checked it echos 1

if dnr is not checked I get the error and echos 0

Here is the relevent part of my code:

<?php
if(isset($Submit)){

$db = mysql_connect('localhost', 'user','');

mysql_select_db('census',$db);

if ($dnr == "") {
  ($dnr = "0");
}
else{
  ($dnr ="1");
}
echo $dnr;

$query=mysql_query("INSERT INTO table SET DNR='$dnr'");
}

else
{
?>
<div align="center">
<form method="post" action="<?php echo $PHP_SELF?>">
....

<input type="checkbox" name="dnr">
....
<input type="submit" name="Submit" value="Submit">
</form>

[kevinsequeira]

try this

if(!isSet($dnr)){
$dnr = "0";
}

instead of

if ($dnr == "") {
($dnr = "0");
}
else{
($dnr ="1");
}

[beach_nc]

that is it!!!

You guys amaze me... why did I bother buying a PHP book?