Email Verification/Validation - Error - php

Question

I think this post may appear to be as an "off" topic to others. But it'll be a great thank if you help me out with this.
I found some email verification code on the web. Somehow, I find it confusing at first but when I began to understand it and put it on my code. There's a error and I don't know how.
Problems:
The email verification code.
Proper syntax/use of the code.
Code:
<?php
if(isset($_POST['submit']))
{
$a = $_POST['username'];
$b = $_POST['password'];
$c = $_POST['firstname'];
$d = $_POST['lastname'];
$e = $_POST['month'];
$f = $_POST['day'];
$g = $_POST['year'];
$h = $_POST['contact'];
$i = $_POST['email'];
$j = $_POST['confirm'];
$code = md5(uniqid(rand()));
include("dbconnect.php");
$query = "SELECT * FROM `users`.`info` WHERE `username`='".$a."' AND `email_address`='".$i."'";
$queryQuery=$con->query($query);
$checker = mysqli_num_rows($queryQuery);
if (($a && $b && $c && $d && $h && $i && $j) == "")
{
print "<script type=text/javascript>
alert('All fields are required');
</script>";
}
else
{
if ($checker == 0 && $b != $j)
{
print "<script type=text/javascript>
alert('Password Mismatch');
</script>";
}
else if($checker == 0)
{
//print $a,$b,$c,$d,$e,$f,$g,$h,$i;
$insertQuery="INSERT INTO `users`.`info` (`username`,`password`,`firstname`,`lastname`,`month`,`day`,`year`,`contact_number`,`email_address`,`confirm_code`) VALUES ('$a','$b','$c','$d','$e','$f','$g','$h','$i','$code')";
$insertQueryResult=$con->query($insertQuery);
if ($insertQueryResult)
{
// send e-mail to ...
$to=$i;
// Your subject
$subject="Your confirmation link here";
// From
$header="From Admins of Publisita.com";
// Your message
$message="Your Comfirmation link \r\n";
$message.="Click on this link to activate your account \r\n";
$message.="http://www.gmail.com/confirmation.php?passkey=$code";
// send email
$sentmail = mail($to,$subject,$message,$header);
}
// if not found
else
{
print "<script type=text/javascript>
alert('Not found your email in our database')
</script>";
}
// if your email succesfully sent
if($sentmail)
{
print "<scrpit type=text/javascript>
alert('Your Confirmation link Has Been Sent To Your Email Address')
</script>";
}
else
{
print "<script type=text/javascript>
alert('Cannot send Confirmation link to your e-mail address')
</script>";
}
}
print "<script type=text/javascript>
alert('Successfully Registered');
</script>";
}
else
{
print "<script type=text/javascript>
alert('Information are already been used');
</script>";
}
}
}
?>
It'll be a great thing if someone helped me out

Answer 1

This line:
if (($a && $b && $c && $d && $h && $i && $j) == "")
is not valid syntax. If you want to make sure these values aren't empty you will need to check them individually (you also want to use or (||) since only one has to be empty for you to show your error. Your current code would require all of them to be empty):
if ($a == "" || $b == "" ....) // or if (empty($a) || empty($b) ....)
or come up with a more concise way to do this:
$fields = array($a, $b, $c, $d, $h, $i, $j);
if (count(array_filter($fields)) !== count($fields))
The code above takes all of the values to be checked an puts them into an array. It then calls array_filter() to remove any values that are false (an empty string is type juggled to be Boolean false). If the number of remaining elements doesn't equal the starting number of elements then one or more were empty and you need to show your error.
As pointed out by #NicolasDefranoux you are wide open to SQL injections. Make sure you close that hole before publishing your code.