php - Notice: Undefined index

I have a checkbox which can make a post password protected-

Password protect? 

My Php tries to post-

 $password = htmlspecialchars(strip_tags($_POST['password']));

I get the undefined index error.

Now, if I try to check first if the password was set, I get the same error executing-

$sql = "INSERT INTO blog (timestamp,title,entry,password) VALUES ('$timestamp','$title','$entry','$password')";

$result = mysql_query($sql) or print("Can't insert into table blog.
" . $sql . "
" . mysql_error());

How do I fix it? Do I have to do it for every field like title text box and all?

Answer

Why are you stripping tags and escaping a boolean value? You could just do it like this:

$password = (isset($_POST['password']) && $_POST['password'] == 1) ? 1 : 0;

or:

$password = isset($_POST['password']) ? (bool) $_POST['password'] : 0;