changepass.php:
<?php
include('core/init.inc.php');
?>
<html>
	<head>
		<title>CHANGE PASSWORD</title>
	</head>
	<body>
		<form action="changepass.php?act=true" method="post">
			<table cellpadding="2" cellspacing="2" border="1">
			<tr>
				<td colspan="2"><label><b>Change Password</b></label></td>
			</tr>
			<tr>
				<td>Old Password:</td>
				<td><input type="password" value="" name="pass" /></td>
			</tr>
			<tr>
				<td>New Password:</td>
				<td><input type="password" value="" name="cpass" /></td>
			</tr>
			<tr>
				<td>Confirm New Password:</td>
				<td><input type="password" value="" name="crepass" /></td>
			</tr>
			<tr>
				<td colspan="2"><input type="submit" value="Change Password" name="submit" /></td>
			</tr>
		</form>
		
		<?php
		
		if ($_GET['act'] == true){
			if ($_POST['submit']){
				$user = $_SESSION['user_username'];
				$pass = htmlspecialchars($_POST['pass']);
				$cpass = htmlspecialchars($_POST['cpass']);
				$crepass = htmlspecialchars($_POST['crepass']);
				
				if ($pass && $cpass && $crepass){
					$query1 = sprintf("SELECT * FROM users WHERE user_username='$user'", mysql_real_escape_string($user_username));
					while ($row = mysql_fetch_assoc($query1)){
						$dbpass = $row['pass'];
					}
					if ($pass == $dbpass){
						if ($cpass == $crepass){
							mysql_query("UPDATE users SET user_password='$crepass' WHERE user_username='$user'");
							echo "<script>
									alert('Your password has been changed!');
								</script>
								<meta http-equiv='refresh' content='1;url=index.php'>";
						} else {
							echo "The passwords in both of the fields do not match!";
						}
					} else {
						echo "The password is incorrect.";
					}
				} else { 
					echo "Please fill in all of the fields.";
				}
			}
		}
		
		?>
		
	</body>
<html>
