PHP writing to MYSQL is variable equals 0 - php

Question

I am trying to write to my database if a variable is equal to 0. The problem is that it still writes to the database even when the variables equals 1. What is wrong??
echo $new_user;
if ($new_user == 0) {
//SENT NEW USER WELCOME MESSAGE
$adminid = '9';
$welcomemessagetitle = 'Welcome to The site';
$welcomemessagecontent = 'Hello and welcome';
$addmessages = "INSERT into `user_messages`(`to_user`,`from_user`,`title`,`content`)
VALUES ('$userid','$adminid','$welcomemessagetitle','$welcomemessagecontent');";
$query = mysql_query($addmessages) or die(mysql_error());
//SET USER AS NOT NEW USER
$newuservalue = '1';
$notnewuser = "UPDATE users SET new_user = $newuservalue WHERE id = $userid" ;
$query2 = mysql_query($notnewuser) or die(mysql_error());
} elseif ($new_user == 1) {};
UPDATE FULL CODE::
<?php
session_start();
include "../includes/db_connect.php";
///profile/index.php
if($_SESSION['id'])
{
$username = $_SESSION['username'];
$userid = $_SESSION['id'];
//WRITE FIRST TIME LOGIN INFORMATION TO DATABASE
$sql="SELECT new_user from `users` WHERE `id`= $userid ";
$res=mysql_query($sql) or die(mysql_error());
while($row=mysql_fetch_assoc($res)) $new_user = $row['new_user'] ;
echo $new_user;
if ($new_user == 0) {
//SENT NEW USER WELCOME MESSAGE
$adminid = '9';
$welcomemessagetitle = 'Welcome to Escorvee';
$welcomemessagecontent = 'Hello and welcome';
$addmessages = "INSERT into `user_messages`(`to_user`,`from_user`,`title`,`content`)
VALUES ('$userid','$adminid','$welcomemessagetitle','$welcomemessagecontent');";
$query = mysql_query($addmessages) or die(mysql_error());
//SET USER AS NOT NEW USER
$newuservalue = '1';
$notnewuser = "UPDATE users SET new_user = $newuservalue WHERE id = $userid" ;
$query2 = mysql_query($notnewuser) or die(mysql_error());
} elseif ($new_user == 1) {};
}
?>

Answer 1

It the variable $new_user is the value 1 then your code won't be executed so I would guess one of the following applies:
$new_user isn't 1.
The database is being modified from another location.
Your script is being called twice.
To work out which you will have to provide more information in your question.