How to calculate the difference in example below - php

Question

I want to calculate difference between the "Total Marks" in a question, and the text inputs for each answer in a question. Also if a question has only one answer, then it should display the text input as a readonly and display the same value as the number under the "Total Mark" for that question in that text input.
Below is a screenshot which shows the table and the written problem I have with both scenarios:
Below is the current jquery variable which should be doing the calculation and display the readonly textbox when necessary. But at the moment it is not working. Also at the moment I have display the number for total marks to be fixed as "5" when doing the calculations, well this is incorrect as that it should be the number for within each row, so I believe the variable $sessionMarks that should be the number, not 5.
$(function(){
var questions = $('#markstbl td[class*="_ans"]').length-1;
//disable single entry
for (var i=0;i<=questions;i++){
if($("[class*=q"+i+"_mark]").length ==1){
$("[class*=q"+i+"_mark]").attr("disabled","disabled")
}
}
//find each question set and add listeners
for (var i=0;i<=questions;i++){
$('input[class*="q'+i+'"]').keyup(function(){
var cl = $(this).attr('class').split(" ")[1]
var questionno = cl.substring(cl.indexOf('q')+1,cl.indexOf('_'))
var t=0;
$("[class*=q"+questionno+"_mark]").each(function(){
var num = (isNaN(parseInt($(this).val())))?0:parseInt($(this).val());
t+=parseInt(num);
})
var fixedno = 5;
$(".q"+questionno+"_ans").text((t>fixedno)?fixedno:t);
})
}
})
Below is the code for the table, from the query it outputs the details of each question from the database and then it displays it in a table:
<?php
$assessment = $_SESSION['id'] . $sessionConcat;
include('connect.php');
$query = "SELECT q.SessionId, s.SessionName, q.QuestionId, q.QuestionContent, an.Answer, q.QuestionMarks
FROM Session s
INNER JOIN Question q ON s.SessionId = q.SessionId
JOIN Answer an ON q.QuestionId = an.QuestionId AND an.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
$searchQuestionId = array();
$searchQuestionContent = array();
$searchAnswer = array();
$searchMarks = array();
// Fetch the results into an array
// get result and assign variables (prefix with db)
$stmt->bind_result($dbSessionId, $dbSessionName, $dbQuestionId, $dbQuestionContent, $dbAnswer, $dbQuestionMarks);
while ($stmt->fetch()) {
$searchQuestionId[] = $dbQuestionId;
$searchQuestionContent[] = $dbQuestionContent;
$searchAnswer[] = $dbAnswer;
$searchMarks[] = $dbQuestionMarks;
}
?>
....
<tbody>
<tr>
<?php
$previous_question_id = null;
$rowspans = array_count_values($searchQuestionId);
$output = "";
$questionid = 0; //whole question
$questionno = 0; //part of question
foreach ($searchQuestionContent as $key => $question) {
if ($previous_question_id != $searchQuestionId[$key]){
$questionno=0;
}
// removed logic, not necessary to set empty strings if you're skipping them
$output.= '<tr class="questiontd">' . PHP_EOL;
if ($previous_question_id != $searchQuestionId[$key]) {
$output.= '<td class="questionnumtd" name="numQuestion" rowspan="' . $rowspans[$searchQuestionId[$key]] . '">' . htmlspecialchars($searchQuestionId[$key]) . '</td>' . PHP_EOL;
$output.= '<td class="questioncontenttd q{$questionno++}_mark{$questionid}" rowspan="' . $rowspans[$searchQuestionId[$key]] . '">' . htmlspecialchars($question) . '</td>' . PHP_EOL;
}
$output.= '<td class="answertd" name="answers[]">';
$output.= $searchAnswer[$key];
$output.= '</td>';
$output.= '<td class="answermarkstd"><input class="individualMarks" q_group="1" name="answerMarks[]" id="individualtext" type="text" /></td>' . PHP_EOL;
if ($previous_question_id != $searchQuestionId[$key]) {
$output.= '<td class="noofmarkstd q{$questionid++}_ans" q_group="1" rowspan="' . $rowspans[$searchQuestionId[$key]] . '">' . htmlspecialchars($searchMarks[$key]) . '</td>' . PHP_EOL;
}
// moved this to the end
if ($previous_question_id != $searchQuestionId[$key]) {
$previous_question_id = $searchQuestionId[$key];
}
}
echo $output;
?>
</tr>
</tbody>
Update:
In the sample HTML which is in this fiddle, I can get it to work (except I want the calculation to be total marks minus number entered in text input, not what it is doing now which is when I enter a number in text input it performs an addition from 0 to whatever number entered in text input), but when I tried to edit the code above to do the same thing, then it doesn't work, nothing happens.
The sample html is below:
<form id="Marks" action="/u0867587/Mobile_app/individualmarks.php" method="post">
<table border='1' id='markstbl'>
<thead>
<tr>
<th class='questionth'>Question No.</th>
<th class='questionth'>Question</th>
<th class='answerth'>Answer</th>
<th class='answermarksth'>Marks per Answer</th>
<th class='noofmarksth'>Total Marks</th>
</tr>
</thead>
<tbody>
<tr class="questiontd">
<td class="questionnumtd" name="numQuestion" rowspan="3">1</td>
<td class="questioncontenttd" rowspan="3">Name three features in a ROM</td>
<td class="answertd" name="answers[]">A</td>
<td class="answermarkstd">
<input class="individualMarks q0_mark_0" q_group="1" name="answerMarks[]" id="individualtext" type="text" />
</td>
<td class="noofmarkstd q0_ans" q_group="1" rowspan="3">5</td>
</tr>
<tr class="questiontd">
<td class="answertd" name="answers[]">B</td>
<td class="answermarkstd">
<input class="individualMarks q0_mark_1" q_group="1" name="answerMarks[]" id="individualtext" type="text" />
</td>
</tr>
<tr class="questiontd">
<td class="answertd" name="answers[]">D</td>
<td class="answermarkstd">
<input class="individualMarks q0_mark_2" q_group="1" name="answerMarks[]" id="individualtext" type="text" />
</td>
</tr>
<tr class="questiontd">
<td class="questionnumtd" name="numQuestion" rowspan="1">2</td>
<td class="questioncontenttd" rowspan="1">Here is a single answer</td>
<td class="answertd" name="answers[]">True</td>
<td class="answermarkstd">
<input class="individualMarks q1_mark_0" q_group="1" name="answerMarks[]" id="individualtext" type="text" />
</td>
<td class="noofmarkstd q1_ans" q_group="1" rowspan="1">5</td>
</tr>
</tbody>
</table>
</form>
Below is what the database tables looks like, (this will follow the same data as the ones in the screenshot)
Session Table: (Where the exam details is stored)
SessionId SessionName
1 AAA
Question Table: (Where questions for each exams are stored)
SessionId QuestionId QuestionContent Total Marks
1 1 Name three features in a ROM 5
1 2 Here is a single answer 5
Answer Table: (Stores answers for each question in each exam)
AnswerId(auto) SessionId QuestionId Answer
1 1 1 A
2 1 1 B
3 1 1 D
4 1 2 True
Individual_Answer Table: (Stores each individual mark for each individual answer)
AnswerId AnswerMarks
1 2
2 2
3 1
4 5

Answer 1

It is not good practice to get and put values from html elements using html() which somehow belong to calculation or integers values, Therefore always use hidden fields for this type of problems, like I have included two hidden fields one for original value and one for the final value and at the end you can get the total marks values easily from the hidden field.
The code is updated for dynamic data. Use your own code for queries, mine is a rough code.
<html>
<head>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
$(function() {
var questions = $('#markstbl td[class*="_ans"]').length;
//disable single entry
for (var i=1;i<=questions;i++){
if($("[class*=q"+i+"_marks]").length ==1){
var t_marks = $("[class*=q"+i+"_ans]").html();
alert(t_marks);
$("[class*=q"+i+"_marks]").val(t_marks).attr("disabled","disabled");
//$("[class*=q"+i+"_mark]").attr("disabled","disabled");
}
}
//find each question set and add listeners
for (var i=0;i<=questions;i++){
$('input[class*="q'+i+'"]').keyup(function(){
var cl = $(this).attr('class').split(" ")[1]
var questionno = cl.substring(cl.indexOf('q')+1,cl.indexOf('_'));
var tot_marks = $(".q"+questionno+"_ans_org").val();
var ans_t=0;
$("[class*=q"+questionno+"_marks]").each(function(){
var num = (isNaN(parseInt($(this).val())))?0:parseInt($(this).val());
ans_t+=parseInt(num);
});
ans_t=tot_marks-ans_t;
var ans = (parseInt(ans_t)<0)?tot_marks:ans_t;
$(".q"+questionno+"_ans").val(ans);
$(".q"+questionno+"_ans_text").html(ans);
});
}
});
</script>
</head>
<body>
<form id="Marks" action="/u0867587/Mobile_app/individualmarks.php" method="post">
<?php
$ident = mysqli_connect('localhost','root','');
mysqli_select_db($ident,'testdata');
$query = "SELECT q.SessionId, s.SessionName, q.QuestionId, q.QuestionContent, an.Answer, q.QuestionMarks
FROM session s
INNER JOIN question q ON s.SessionId = q.SessionId
JOIN answer an ON q.QuestionId = an.QuestionId AND an.SessionId = q.SessionId
ORDER BY q.QuestionId, an.Answer
";
$res = mysqli_query($ident,$query);
$searchQuestionId = array();
$searchQuestionContent = array();
$searchAnswer = array();
$searchMarks = array();
while ($row = mysqli_fetch_array($res)) {
$searchQuestionId[] = $row['QuestionId'];
$searchQuestionContent[] = $row['QuestionContent'];
$searchAnswer[] = $row['Answer'];
$searchMarks[] = $row['QuestionMarks'];
}
?>
<form id="Marks" action="/u0867587/Mobile_app/individualmarks.php" method="post">
<table border='1' id='markstbl'>
<thead>
<tr>
<th class='questionth'>Question No.</th>
<th class='questionth'>Question</th>
<th class='answerth'>Answer</th>
<th class='answermarksth'>Marks per Answer</th>
<th class='noofmarksth'>Total Marks</th>
</tr>
</thead>
<tbody>
<?php
$row_span = array_count_values($searchQuestionId);
$output = '';
$rowCount = 1;
$newQuest_id = true;
foreach($searchQuestionId as $key=>$questionId){
if($newQuest_id == true){
$output.= '<tr class="questiontd">';
$output.= '<td class="questionnumtd" name="numQuestion" rowspan="'.$row_span[$questionId].'">'.$questionId.' <input type="hidden" name="q'.$questionId.'_ans_org" class="q'.$questionId.'_ans_org" value="'.$searchMarks[$key].'"><input type="hidden" name="q'.$questionId.'_ans" class="q'.$questionId.'_ans" value="'.$searchMarks[$key].'"></td>';
$output.= '<td class="questioncontenttd" rowspan="'.$row_span[$questionId].'">'.$searchQuestionContent[$key].' </td>';
}
$output.= '<td class="answertd" name="answers[]">'.$searchAnswer[$key].'</td>';
$output.= '<td class="answermarkstd">';
$output.= '<input class="individualMarks q'.$questionId.'_marks" q_group="1" name="answerMarks[]" id="individualtext" type="text" />';
$output.= '</td>';
if($newQuest_id == true){
$output.= '<td class="noofmarkstd q'.$questionId.'_ans_text" q_group="1" rowspan="'.$row_span[$questionId].'">'.$searchMarks[$key].'</td>';
$newQuest_id = false;
}
$output.= '</tr>';
if($row_span[$questionId] == $rowCount){
$newQuest_id = true;
}
$rowCount++;
}
echo $output;
?>
</tbody>
</table>
</form>
</form>
</body>
</html>