How to validate form input on the same page by using random numbers?

Question

Would be awesome if you could help me out! I am trying to build a simple page to display random math questions. The answers should be typed in by the user and should be validated on the same page, giving him feedback on success and failure.

The problem is that by submitting the form input to the same page (I called it "form6.php") the page reloads and a new set of numbers is generated - that is why the "solution" variable is newly defined and cannot be used to test the accuracy of the user's answer.

This is the code I have so far (works fine for fixed numbers but fails with the random number generation):

<?php
$number1 = rand(1,100);
$number2 = rand(1,100);
$solution = $number1+$number2;

echo "$number1+$number2=?";

?>

<form action="form6.php" method="post">
Your Answer:<br>
<input type="integer" name="answer">
<input type="Submit" value="Submit!">
</form>

<?php
if(isset($_POST['answer'])){
    if ($_POST["answer"] == $solution)
    {echo "That's right";}
    else
    {echo "That's wrong!";};
}

?>

Any help is highly appreciated! Since I am not a professional coder, the more specific you can get, the better!

Answer 1

A POSTed form will reload your PHP script, causing 2 new rand() numbers to be generated. You're going to want to pass the solution in the form.

Edit: I updated the answer to show a quick solution for using random operands for verification. This was simply done by switching through a random integer. Please note that when using - or / you may receive non-integer numbers (3 / 58 or 15 - 86), so you may want to add some custom logic to prevent this.

<?php
$number1 = rand(1,100);
$number2 = rand(1,100);

switch(rand(0,3)) {
    case 0:
        $solution = $number1 + $number2;
        echo "$number1+$number2=?";
        break;
    case 1:
        $solution = $number1 - $number2;
        echo "$number1-$number2=?";
        break;
    case 2:
        $solution = $number1 * $number2;
        echo "$number1*$number2=?";
        break;
    case 3:
        $solution = $number1 / $number2;
        echo "$number1/$number2=?";
        break;
}
?>

<form action="form6.php" method="post">
    Your Answer:<br><input type="integer" name="answer">

    <input type="hidden" name="solution" value="<?php echo $solution; ?>">
    <input type="Submit" value="Submit!">
</form>

<?php
if(isset($_POST['answer']) && isset($_POST['solution'])) {
    if ($_POST["answer"] == $_POST['solution']) {
        // Valid
    } else {
        // Incorrect
    }
}
?>

Answer 2

If you don't want to include the solution in your form (be it hidden), you have to store solutions in a separate text file in which you can, for instance, serialize your data.

Alternatively, you can use sessions or cookies.

But you have to store the solution somewhere.

Here is an attempt with sessions:

<?php
session_start();

$nb1 = rand(1,100);
$nb2 = rand(1,100);

$_SESSION['number1'] = $nb1;
$_SESSION['number2'] = $nb2;
$_SESSION['solution'] = $nb1 + $nb2;

// (...)

if(isset($_POST['answer']))
{
    if ($_POST["answer"] == $_SESSION['solution'])
        {echo "That's right";}
    else
        {echo "That's wrong!";};

    unset($_SESSION['nb1']);
    unset($_SESSION['nb2']);
    unset($_SESSION['nbsolution']);
}

Answer 3

if(isset($_POST['answer'])===true){
    if ($_POST["answer"] == $solution)
    {echo "That's right";}
    else
    {echo "That's wrong!";};
}

If you are using isset($_POST['answer']) you must include === true at the end Also make sure you use instead of integer.

Answer 4

@user3261573,

As pointed out by @Sam, you could pass the value in a hidden field, but, as @Jivan said, a better approach would be using a session to store the solution.

Here's the code:

Ps.: I simplified the code for a better understanding.

<?php
    // Initiate session
    session_start();

    // If the FORM has been submited, verify answer
    if( isset($_SESSION['solution']) === TRUE && $_SESSION['solution'] !== NULL && isset($_POST['answer']) === TRUE && isset($_POST['solution']) == TRUE ){
        if( $_SESSION['solution'] == $_POST['answer'] ){
            echo 'That\'s right';
        }else{
            echo 'That\'s wrong';
        }
    }
    // If the FORM ain't submited yet, display the question
    else{
        // Random numbers
        $number1 = rand(1,100);
        $number2 = rand(1,100);

        // Store solution in session for further comparison
        $_SESSION['solution'] = $number1+$number2;

        // Echo question
        echo "$number1+$number2=?";


        echo '<form action="form6.php" method="post">
        Your Answer:<br>
        <input type="integer" name="answer">
        <input type="Submit" value="Submit!">
        </form>';
    }
?>

If you like it, here's a few tutorials on using PHP SESSIONs:

http://www.w3schools.com/php/php_sessions.asp http://www.php.net/manual/en/session.examples.basic.php

Answer 5

<?php
$number1 = rand(1,100);
$number2 = rand(1,100);

echo "$number1+$number2=?";

?>

<form action="form6.php" method="post">
Your Answer:<br>
<input type="integer" name="answer">
<input type="Submit" value="Submit!">

<input type="hidden" name="n1" value="$number1">
<input type="hidden" name="n2" value="$number2">
</form>

<?php
if(isset($_POST['answer'])){
    $solution = $_POST['n1'] + $_POST['n2'];
    if ($_POST["answer"] == $solution)
    {echo "That's right";}
    else
    {echo "That's wrong!";};
}

?>