Updating mySQL INT with new INT - php

Question

Okay so for a basic outline I'm trying to update a column in my mySQL database dependent on the outcome of my code.
Basically it's rolling dice, if you beat the house it increases your INT by 5 if you loose to the house, it decreases by 5. This is for my own educational purposes and will not be used publicly.
The part that isn't working is the mysq_query("UPDATE") with both win and lose.
if (isset($_POST['roll'])) {
$rand = rand(1, 6);
$rand1 = rand(1, 6);
$rand2 = rand(1, 6);
$rand3 = rand(1, 6);
$score = $rand + $rand1;
$score1 = $rand2 + $rand3;
echo 'You rolled a '.$rand.' and a '.$rand1.' Totalling '.$score;?><br><?
echo 'Your opponent rolled a '.$rand2.' and a '.$rand3.' Totalling '.$score1;?><br><br><?
if ($score > $score1){
echo 'Win';
$coins = $user_data['coins'] + 5;
mysql_query("UPDATE `users` SET `coins` = '$coins' WHERE `user_id` = $user_id");
} else {
echo 'Loose';
$coins1 = $user_data['coins'] - 5;
mysql_query("UPDATE `users` SET `coins` = '$coins1' WHERE `user_id` = $user_id");
}
}
?>
<form action="playdice.php" method="POST">
<input type="submit" name="roll" value="Roll Dice.">
</form>

Answer 1

You dont need the ' around $coins. Those specify that the input is a CHAR, so MySQL is probably trying to insert a CHAR and refusing as it's an INT column.
You also don't appear to have defined a connection to query on.
$mysqli = new mysqli("localhost", "user", "password", "database");
...
if ($score > $score1){
echo "Win";
$coins = $user_data['coins'] + 5;
$mysqli->query("UPDATE `users` SET `coins` = $coins WHERE `user_id` = $user_id");
} else {
echo "Lose";
$coins = $user_data['coins'] - 5;
$mysqli->query("UPDATE `users` SET `coins` = $coins WHERE `user_id` = $user_id");
}
This should work. (Sorry for switching you from the deprecated mysql syntax but I honestly don't remember it, if you're learning you're better off using mysqli anyway).

Answer 2

Put a ' around the $user_id, it's probably a string. removing the quote tells MySQL that it is an integer.