admin-login.php at Weight Loss Recipe Book

<?php 

include('functions/functions_general.php');
include('config.php');


	// BEGIN ACTIONS
	if ($_GET['action'] == 'logout') {
		$_SESSION[$program_prefix . 'admin_username'] = '';
		$_SESSION[$program_prefix . 'admin_password'] = '';
		$_SESSION[$program_prefix . 'admin_id'] = '';
		$_SESSION[$program_prefix . 'admin_level'] = '';
		$result_div .= getResultDiv('You have been logged out.','success');
	}
	if ($_POST['action'] == 'admin_login') {
		$i = 0;
		if (!$_POST['administrators_username']) {
			$error[$i] = "Please enter your username.";
			$i++;
		}
		if (!$_POST['administrators_pass']) {
			$error[$i] = "Please enter a password.";
			$i++;
		}
		if ($i == 0) {
			$sql = '
				SELECT *
				FROM ' . $program_prefix . 'administrators
				WHERE administrators_username = "' . $_POST['administrators_username'] . '" and
					administrators_pass = PASSWORD("' . $_POST['administrators_pass'] . '")';
			$user_result = mysql_query($sql);
				echo mysql_error();
			if (mysql_num_rows($user_result) < 1) {
				$error[$i] = "That username and password don't match, please try again.";
				$i++;
			} else {
				$admin = mysql_fetch_array($user_result);
				$_SESSION[$program_prefix . 'admin_username'] = $admin['administrators_username'];
				$_SESSION[$program_prefix . 'admin_password'] = $admin['administrators_pass'];
				$_SESSION[$program_prefix . 'admin_id'] = $admin['administrators_id'];
				$_SESSION[$program_prefix . 'admin_level'] = $admin['administrators_level'];
				header("Location:admin-home.php");
			}
		}
		$result_div .= getResultDiv($error);
	}

?>
<head>
	<link href="styles/admin.css" rel="stylesheet" type="text/css"></link>
	<title>Admin Log In</title>
</head>
<body>
	<div class="main">	
		<h1>Admin Log In</h1>
		<?php echo $result_div; ?>
		<form action="admin-login.php" method="post">
			<input name="action" type="hidden" value="admin_login" />
			<table>
				<tr>
					<td>Username</td>
					<td><input type="text" name="administrators_username" /></td>
				</tr>
				<tr>
					<td>Password</td>
					<td><input type="password" name="administrators_pass" /></td>
				</tr>
			</table>
			<input type="submit" value="Log In" />
		</form>
	</div>
</body>