bind_param() Issues - php

Question

I am getting issues with the bind_param function. I will post all the information below.
Error:
Fatal error: Call to a member function bind_param() on a non-object in /home4/lunar/public_html/casino/blogpost.php on line 88
MySQL Error:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ':user, :title, :message, :image, :category, NOW())' at line 1
Query:
$user = $_COOKIE['user'];
$title = $_POST['title'];
$message = $_POST['message'];
$image = $_POST['image'];
$category = $_POST['category'];
$stmt = $mysqli->prepare("INSERT INTO `lunar_casino`.`posts` (`id`, `by`, `title`, `message`, `image`, `category`, `date`) VALUES(NULL, :user, :title, :message, :image, :category, NOW())");
echo $mysqli->error;
$stmt->bind_param(":user", $user);
$stmt->bind_param(":title", $title);
$stmt->bind_param(":message", $message);
$stmt->bind_param(":image", $image);
$stmt->bind_param(":category", $category);
$stmt->execute();
if(!$stmt){
echo "<font color='red'><b>There has been an error with our database! Please contact the website administrator!</b></font><br /><br />";
echo $mysqli->error;
} else {
echo "<font color='green'><b>You have successfully added a blog post!</b></font><br /><br />";
}
Any ideas why its like this?

Answer 1

As Rocket Hazmat mentioned you can only use question marks as bind parameter place holder.
You should do something similar:
$stmt = $mysqli->prepare("INSERT INTO `lunar_casino`.`posts` (`id`, `by`, `title`, `message`, `image`, `category`, `date`) VALUES(NULL, ?, ?, ?, ?, ?, NOW())");
$stmt->bind_param("sssss", $user, $title, $message, $image, $category);
More details: http://www.php.net/manual/en/mysqli-stmt.bind-param.php

Answer 2

$stmt->bind_param("sssss", $user, $title, $message, $image, $category);
on the first argument the s = string and i = integer. You need to specify which type of value you want to add to the database. If you want to add 5 values that are strings to the database then write 'sssss' if you want to insert 5 integers then write 'iiiii' if you have some integers values and some string values then you can adjust accordingly.
//so if your values are all strings then this would be correct :
$stmt->bind_param("sssss", $user, $title, $message, $image, $category);
//so if your values are all integers then this would be correct :
$stmt->bind_param("iiiii", $user, $title, $message, $image, $category);
//if the first 2 are integers and the other 3 strings then this would be correct :
$stmt->bind_param("iisss", $user, $title, $message, $image, $category);
and so on.