Problem with my PHP server-side validation code - php

Question

I have a form in a file register.php, and it posts to registerPost.php. Inside registerPost.php, I check against a few validation rules, then if any of them are flagged, I return to the first page and print the errors. In theory, that should work. But the validation goes through with no problems, even when I leave everything blank.
Here's the code in question:
$_SESSION["a"] = "";
$_SESSION["b"] = "";
$_SESSION["c"] = "";
$_SESSION["d"] = "";
$_SESSION["e"] = "";
$_SESSION["f"] = "";
$_SESSION["g"] = "";
if(empty($userEmail))
{
$_SESSION["a"] = "You must enter your email.";
}
if(!validEmail($userEmail))
{
$_SESSION["a"] = "Improper Email Format";
}
if(empty($password))
{
$_SESSION["b"] = "You must enter a password.";
}
if(strlen($password) < 5 || strlen($password) > 0)
{
$_SESSION["b"] = "Password must be at least 5 characters.";
}
if($password != $confPassword)
{
$_SESSION["c"] = "Passwords do not match";
}
if(empty($firstName))
{
$_SESSION["d"] = "First Name Required";
}
if(empty($lastName))
{
$_SESSION["e"] = "Last Name Required";
}
if(mysql_num_rows(mysql_query("SELECT * FROM users WHERE email = '$email'")) > 0)
{
$_SESSION["f"] = "This email address already exists in our database.";
}
if(!empty($_SESSION["a"]) || !empty($_SESSION["b"]) || !empty($_SESSION["c"]) || !empty($_SESSION["d"]) || !empty($_SESSION["e"]) || !empty($_SESSION["f"]))
{
header('Location: register.php');
}
Perhaps there is a more straightforward way to do this?

Answer 1

I like this way of registering all errors:
$errors = array();
if (empty($foo1))
$errors[] = "foo1 can't be left blank!";
else if (!preg_match(' ... ', $foo1))
$errors[] = "foo1 was not filled out correctly!";
if (empty($foo2))
$errors[] = "foo2 can't be left blank!";
// ...
if (empty($errors)) {
// do what you need
} else {
// notify the user of the problems detected
}
Do you really need to change the page by header?

Answer 2

I tried your code and it works for me.
Guessing from $username,$email and so on, I think you're doing some sanitizing on the $_POST data. If so, you should dump the $username, etc. to see, if that procedure is putting something in these variables.
Anyway, I like this way of validation better:
$errors = array();
if(empty($username))
{
$errors['username'] = 'Username cannot be empty!';
}
...
$_SESSION['errors'] = $errors;
if(count($errors) > 0) //Redirect...