Using data from an user that is logged in with php - php

Question

I have created a login.php that works and keeps the user logged in with session.
Now, User has an option to use his "money" to buy something, so he clicks on "buy" and it opens "transfer.php" which is this below.
<?php
session_start();
$servername = "";
$username = "";
$password = "";
$dbname = "";
// Create connection header("Location:transfer2.php");
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "UPDATE user SET money=money-2 WHERE id=2";
if ($conn->query($sql) === TRUE) {
exit();
} else {
echo "Error updating record: " . $conn->error;
}
$conn->close();
?>
Now, this part:$sql = "UPDATE user SET money=money-2 WHERE id=2"; I want this script to automaticly find the id from the user that is logged in currently.
Im trying to figure this out, and I am just lost.
Thanks in advance.

Answer 1

In the login script, set a session variable to the user's ID. Then you can use this session variable in other scripts.
$sql = "UPDATE user SET money=money-2 WHERE id = ?";
if ($stmt = $conn->prepare($sql)) {
$stmt->bind_param("i", $_SESSION['user_id']);
if ($stmt->execute()) {
exit();
} else {
die("Error updating record: " . $stmt->error);
}
} else {
die("Error updating record: " . $conn->error);
}