Hello i im confuzed with this problem, i have converted the php code into the right format MySQLi and i get this wierd error Notice: Array to string conversion in C:\xampp\htdocs\Training\core.php on line 25 So i dont know where is the problem in the login.php or core.php look at the codes and please tell me where should i correct something thank you :)

function getUserData($field) {
        $DBServer = 'localhost';
        $DBUser   = 'root';
        $DBPass   = '';
        $DBName   = 'upstrey';
        $conn = new mysqli($DBServer, $DBUser, $DBPass, $DBName);

        if ($conn->connect_error) {
            die("Connection failed: " . $conn->connect_error);
        }

        $sql = "SELECT `$field` FROM `users` WHERE `ID`='".$_SESSION['user_id']."'"; // this is the line 25 in the error
        $result = $conn->query($sql);

        if ($result->num_rows > 0) {
            if($row = fetch_assoc($result)) {
                return $row["$field"];
            }
            // so i want to make getUserData function so i can use it like getUserData('First Name') in other files
        }
        $conn->close();
    }

login.php

if($result->num_rows > 0) {
                    session_start();
                    $user_id = mysqli_fetch_row($result);
                    $_SESSION['user_id'] = $user_id;
                    /*$_SESSION['user_id'] = "1"; <-- this line giving me data from the first ID in the database*/
                    header('Location: home.php');
                    echo "Email and Password Accepted";
                } else {
                    session_start();
                    $_SESSION['user_id'] = ''; // and also tell me if this line is ok ?
                    echo "Invalid Email or Password";
                }

Thank you again

Line 4 in login.php stores an array (a result row) in your session variable. I think it should be something like this:

$row = mysqli_fetch_row($result);
$_SESSION['user_id'] = $row['user_id']; // you only want to store the user id, so change it to the right column name.

Thank you now doesn't show any error but the values arent showing any other options ?

Anyone with different solution ?

I know im not alowed to do this but Anyone ?

header('Location: home.php');
echo "Email and Password Accepted";

header redirect before text output, will never provide confirmation
put confirmation in home.php

can't see any code trying to output array values.
what: values are,
where: not showing

I don't think anyone minds a 'bump', people who may answer are in all 24 timezones

Yeah, i dont know why that is still there and i know it will never be shown :D
And yeah i forgoted to put the header.php code, but its just simple 2 PHP lines which is getting data from the core.php

<?php
    $firstname = getUserData("First Name");
    $lastname = getUserData("Last Name");
    echo "<a style='color: white;'>$firstname $lastname</a>";
?>