Test IF with multiple conditions in PHP

I didn't quite understand if you're referring to Nabla's meaning or this one:

<?php
if( $age < 14 ) // $if $age is less than < 14
echo 'You are under 14 years old';
else if( $age <= 18 ) // else, if $age is less than or equal to 18
echo 'You are between 14 and 18 years old';
else if( $age <= 25 ) // else, if $age is less than or equal to 25
echo 'You are between 19 and 25 years old';
else if( $age <= 64 ) // else, if $age is less than or equal to 64
echo 'You are between 26 and 64 years old';
else // otherwise
echo 'You are over 64 years old!';
?>

I just realized that I should use an "or" instead of an "&".
Thank you very much.

Hello billibob, you're making things complicated with all those parentheses, here's the same code in a bit simpler form:

<?php
mysql_connect("localhost", "root", "");
mysql_select_db("forum");

$name = mysql_real_escape_string(htmlspecialchars($_POST['name']));

$message = mysql_real_escape_string(htmlspecialchars($_POST['message']));

if ($name == "" && $message == "" )
{
echo 'not filled';
}
else
{
mysql_query('INSERT INTO message VALUES("", "'.$name.'", "'.$message.'")');
header('Location: index.php');
}

?>

Here is my problem, I am testing 2 fields of a form to make sure they are filled.
The problem is that as soon as one is filled, even if the other is empty, it still goes through.

Here is my PHP script:

<?php
mysql_connect("localhost", "root", "");
mysql_select_db("forum");

$nom = mysql_real_escape_string(htmlspecialchars($_POST['nom']));
$message = mysql_real_escape_string(htmlspecialchars($_POST['message']));

if (($nom == "") && ($message == ""))
echo 'not filled';

else {
mysql_query('INSERT INTO message VALUES("", "'.$nom.'", "'.$message.'")');
header('Location: index.php');}

?>