Change page from next button with id

See more:

Javascript

HTML

PHP

I'm doing a program where I have several exercises with their id (e.g. Id = 1, 2, 3 ...) What I would like to do is that once the user is in an exercise, he can press the Next button and take him to the next exercise, for example id + 1.

Below I show what I've done. Can you help me?

What I have tried:

I tried to make the code for Next as follows:

var i=$_GET['id']);

function getNext()
{
    var = var + 1; //increase var by one
return var;
}

<button class="buttonNext" onclick="getNext" >Next Question</button>

Here is my code:

<?php
// Start the session
session_start();
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "project";

$conn = new mysqli($servername, $username, $password, $dbname);
/*echo*/ $id=$_GET['id'];
$sql = "SELECT * FROM exercises where exercise_id='$id'";
$result = $conn->query($sql); /*Check connection*/
?>

<div id="centered_B" class="header">

<?php
    $row = $result->fetch_assoc();
?>

    <p><?php echo $row["exercise_id"] . ". " . $row["text"]?></p>
    <img width="603" height="auto" src="<?php echo $row["image_path"]?>"><br/><br/>
    <form action='' method='post'>
        <input type="radio" name="choice" value= "1" /><img src="<?php echo $row["image_path_A"] ?>"/><br>
        <input type="radio" name="choice" value= "2" /><img src="<?php echo $row["image_path_B"] ?>"><br>
        <input type="radio" name="choice" value= "3" /><img src="<?php echo $row["image_path_C"] ?>"><br>

        <!-- var_dump($id) -->

    <br><br><br><!--- Select difficulty --->

    <p2>Select difficulty level:</p2>

    <form action='' method='post'>
        <select name="choose" id="choose">>
        <option value="1" <?php if($row["difficulty"]=="1") { echo "selected"; } ?> >1</option>
        <option value="2" <?php if($row["difficulty"]=="2") { echo "selected"; } ?> >2</option>
        <option value="3" <?php if($row["difficulty"]=="3") { echo "selected"; } ?> >3</option>
        <option value="4" <?php if($row["difficulty"]=="4") { echo "selected"; } ?> >4</option>
        <option value="5" <?php if($row["difficulty"]=="5") { echo "selected"; } ?> >5</option>
    </select>

    <br><br><br><!--- Button --->

<!--        <button class="buttonSubmit" >Submit</button>-->
        <input type="submit" name="submit" value="Submit">
        <button class="buttonNext" >Next Question</button>
    </form>

</div><!--- end of centered_B div --->

<?php

if (isset($_POST['submit'])) {
    $user_id = $_SESSION['user_id'];
    $user_check_query = "SELECT * FROM users WHERE id='$user_id'";
    if(isset($_POST['choice'])){
        if(isset($_POST['choose'])){
            $choice_answer=$_POST['choice'];
            $difficulty=$_POST['choose'];
//      */$user_id = $_SESSION['user_id'];*/
            $query = "INSERT INTO answers (exercise_id_fk, student_id, difficulty_student, choice_answer) VALUES ('$id','$user_id', '$difficulty', '$choice_answer')";
            $sql=mysqli_query($conn,$query);
        }
    }
}
?>