How to retrieve incorrect answers from a list of p

Question

With the code below I am trying to retrieve the list of possible answers by first finishing a question's Option Type and then removing the correct answers (Answer field`) from the list of answers.

My question though is that I just need a little help finishing the code off to be able to do this. I am getting an notices in the $row variable where I know I have not called up on it before the if statement to refer to it but my question on that is what is $row variable suppose to be set as or do I need to call $row something else?

Example notice received:

Notice: Undefined variable: row in ... on line ...

Notice: Trying to get property of non-object in ... on line ...

Another is issue if you look at code at the very bottom, when I try to display the incorrect answers <?php echo $incorrect_ans[$key]; ?> It keeps displaying the word Array. Am I calling the array incorrectly? I want it to display the incorrect answers recieved.

Below is the full code

    $query = "SELECT q.SessionId, s.SessionName, q.QuestionId, q.QuestionNo, q.QuestionContent, an.Answer, an.AnswerId, q.QuestionMarks, q.OptionId, o.OptionType
    FROM 
    Question q INNER JOIN Answer an ON q.QuestionID = an.QuestionID
    INNER JOIN Option_Table o ON o.OptionID = q.OptionID
    INNER JOIN Session s ON s.Sessionid = q.Sessionid
    WHERE s.SessionName = ?
    ORDER BY q.QuestionId, an.Answer
       ";

           // prepare query
           $stmt=$mysqli->prepare($query);
           // You only need to call bind_param once
           $stmt->bind_param("s", $assessment);
           // execute query
           $stmt->execute(); 


               // This will hold the search results
            $searchQuestionNo = array();
            $searchQuestionContent = array();
            $totalMarks = array();
            $searchAnswerId = array();
            $searchMarks = array();

            // Fetch the results into an array

           // get result and assign variables (prefix with db)
        $stmt->bind_result($dbSessionId, $dbSessionName, $dbQuestionId, $dbQuestionNo, $dbQuestionContent, $dbAnswer, $dbAnswerId, $dbQuestionMarks, $dbOptionId, $dbOptionType);
              while ($stmt->fetch()) {

                   $specialOptionTypes = array(
            'Yes or No' => array( 'Y', 'N' ),
            'True or False' => array( 'T', 'F' ),
        );

        // Do this for each row:
        if ( array_key_exists( $row->OptionType, $specialOptionTypes ) ) {
            $options = $specialOptionTypes[ $row->OptionType ];
        } else if ( preg_match( '/^([A-Z])-([A-Z])$/', $row->OptionType, $match ) ) {
            $options = range( $match[1], $match[2] );
        } else {
            // issue warning about unrecognized option type
            $options = array();
        }
        $right = str_split( $row->Answer );  // or explode() on a delimiter, if any
        $wrong = array_diff( $options, $right );  

                $searchQuestionNo[] = $dbQuestionNo;
                $searchQuestionContent[] = $dbQuestionContent;
                $incorrect_ans[] = $wrong;
                $searchAnswerId[] = $dbAnswerId;
                $totalMarks[] = $dbQuestionMarks;
                $searchMarks[] = $dbQuestionMarks;
              } 

.... 

          //table row 

          <td class="answertd" name="incorrectanswers[]"><?php
    echo $incorrect_ans[$key];
    ?></td> 

If you want to see the database tables to see what is in each table then have a look below:

DB Table Structure:

Session Table (aka Exam Table)

SessionId(auto)  SessionName
137              XULWQ

Question Table:

SessionId  QuestionId QuestionContent  QuestionNo QuestionMarks  OptionId
137        1          Name 2 Things     1         5               5
137        2          Name 3 Things     2         5               2

Option_Table Table:

OptionId  OptionType
1         A-C
2         A-D
3         A-E
4         A-F
5         A-G
6         A-H

Answer Table:

 AnswerId(auto) SessionId  QuestionId  Answer
   200            137        1           B
   201            137        1           F
   202            137        2           D
   203            137        2           A
   204            137        2           C   

UPDATE:

Only issue now is the layout of the incorrect answers, I want it to display each incorrect answer in its own row per question:

So lets say below are the correct and incorrect answers for each question:

Question Number: 1   Correct Answer(s) B     Incorrect Answers A C D
Question Number: 2   Correct Answer(s) A C   Incorrect Answers B D
Question Number: 3   Correct Answer(s) D     Incorrect Answers A B C

Below shows the current layout and the way it should be laid out:

The code for the current output is this:

<table border='1' id='penaltytbl'>
<thead>
<tr>
<th class='questionth'>Question No.</th>
<th class='answerth'>Incorrect Answer</th></tr>
</thead>
<tbody>
<?php
$row_span = array_count_values($searchQuestionNo);
$prev_ques = '';
foreach($searchQuestionNo as $key=>$questionNo){

?>

<tr class="questiontd">
    <?php
    if($questionNo != $prev_ques){
    ?>
    <td class="questionnumtd q<?php echo$questionNo?>_qnum" rowspan="<?php echo$row_span[$questionNo]?>">
    <?php echo$questionNo?><input type="hidden" name="numQuestion" value="<?php echo$questionNo?>" />
    </td>
    <?php
    }  
    ?>
<td class="answertd"><?php echo implode(',', $incorrect_ans[$key]);?></td>
</tr>
<?php
$prev_ques = $questionNo;
}
?>
</tbody>
</table>

Answer 1

Problem with $row is pretty simple - there is no variable $row defined. Instead of fetching rows you're binding variables to result values, so just replace $row->OptionType with bound variable $dbOptionType and similar $row->Answer with $dbAnswer. To fetch rows you should rather do it this way:

$stmt->execute();
$result = $stmt->get_result();
while ($row = $result->fetch_object()) {
    // ...
}

In example code I don't see also $incorrect_ans variable defined, maybe you're doing it somewhere else but if not then add $incorrect_ans = array() for example there where you're defining other lists (below // This will hold the search results line).

Try doing print_r on $incorrect_ans then you'll see structure of result array, you've got there list of arrays and thats why echo $incorrect_ans[$key]; is resulting in Array. You can do echo implode(',', $incorrect_ans[$key]); and you'll get string with values separated by , character.

I'd suggest to define $specialOptionTypes before while loop, you're not changing that array inside a loop so I suppose there is no reason to recreate it on every iteration.

I noticed also that you're setting name attribute to <td> which does not have such attribute (as far as I know) - maybe you wanted to use some <input>?

<?php

// .........

$query = "SELECT q.SessionId, s.SessionName, q.QuestionId, q.QuestionNo, q.QuestionContent, an.Answer, an.AnswerId, q.QuestionMarks, q.OptionId, o.OptionType
    FROM 
    Question q INNER JOIN Answer an ON q.QuestionID = an.QuestionID
    INNER JOIN Option_Table o ON o.OptionID = q.OptionID
    INNER JOIN Session s ON s.Sessionid = q.Sessionid
    WHERE s.SessionName = ?
    ORDER BY q.QuestionId, an.Answer";

// prepare query
$stmt=$mysqli->prepare($query);
// You only need to call bind_param once
$stmt->bind_param("s", $assessment);
// execute query
$stmt->execute(); 


// This will hold the search results
$searchQuestionNo = array();
$searchQuestionContent = array();
$totalMarks = array();
$searchAnswerId = array();
$searchMarks = array();
$incorrect_ans = array();

// Fetch the results into an array

// get result and assign variables (prefix with db)
$stmt->bind_result($dbSessionId, $dbSessionName, $dbQuestionId, $dbQuestionNo, $dbQuestionContent, $dbAnswer, $dbAnswerId, $dbQuestionMarks, $dbOptionId, $dbOptionType);
$specialOptionTypes = array(
    'Yes or No' => array('Y', 'N'),
    'True or False' => array('T', 'F'),
);
while ($stmt->fetch()) {
    // Do this for each row:
    if (array_key_exists($dbOptionType, $specialOptionTypes)) {
        $options = $specialOptionTypes[$dbOptionType];
    } else if (preg_match('/^([A-Z])-([A-Z])$/', $dbOptionType, $match)) {
        $options = range($match[1], $match[2]);
    } else {
        // issue warning about unrecognized option type
        $options = array();
    }
    $right = str_split($dbAnswer);  // or explode() on a delimiter, if any
    $wrong = array_diff($options, $right);

    $searchQuestionNo[] = $dbQuestionNo;
    $searchQuestionContent[] = $dbQuestionContent;
    $incorrect_ans[] = $wrong;
    $searchAnswerId[] = $dbAnswerId;
    $totalMarks[] = $dbQuestionMarks;
    $searchMarks[] = $dbQuestionMarks;
} 

// .........

for ($key = 0, $cnt = count($incorrect_ans) ; $key < $cnt ; ++$key) : 
?>
<td class="answertd">
    <?php echo implode(',', $incorrect_ans[$key]); ?>
</td>
<?php 
endfor; 
?>