Can't get the value of a data PHP - php

Question

im having trouble getting a result value of a query and the error says.
Notice: Undefined index: prelim in C:\xampp\htdocs\gradingxworking\teacher\student.php on line 85 can someone help me to fix this or some clue to fix this? im just starting to learn php.
<tbody>
<?php $c=1; ?>
<?php foreach($mystudent as $row): ?>
<tr>
<td><?php echo $c; ?></td>
<td class="text-center"><?php echo $row['studid']; ?></td>
<td class="text-center"><?php echo $row['lname'].', '.$row['fname']; ?></td>
<?php $grade = $student->getstudentgrade($row['studid']);?>
//code that cause error line 85--> <td class="text-center"><?php echo $grade['prelim']; ?></td>
</tr>
<?php $c++; ?>
<?php endforeach; ?>
<?php if(!$mystudent): ?>
<tr><td colspan="8" class="text-center text-danger"><strong>*** No Result ***</strong></td></tr>
<?php endif; ?>
</tbody>
the function:
function getstudentgrade($studid){
$q = "select * from studentsubject where studid=$studid";
$r = mysql_query($q);
$data = array();
while($row = mysql_fetch_array($r)){
$data[] = array(
'prelim' => $row['prelim']
);
}
return $data;
}

Answer 1

As #Bara suggested, you need to check the array first before accessing it.
if(isset($grade['prelim']))
I suspect, there is no data for specific studid. Lets see you function.
$data = array();
while($row = mysql_fetch_array($r)){
$data[] = array(
'prelim' => $row['prelim']
);
}
Now, you have created new array $data. But, if there is no record ? your while loop won't be executed and your $data array won't have anything. right ? So, to handle that, you need to check whether there is any data in your array.
Now, second point, which #Mossavari made is also correct. You need to use
$grade[0]['prelim'];
instead of
$grade['prelim'];

Answer 2

after doing
<?php $grade = $student->getstudentgrade($row['studid']);?>
you need to check what $grade holdes. and its better before trying to fetch data from array to make a check like this :
if(isset($grade['prelim']))

Answer 3

Based on your getstudentgrade function you'll have multidimensional array result, you may need to change $grade['prelim'] to $grade[0]['prelim']

Answer 4

Since, every student will have only 1 grade. So, why to use array.
<?php
function getstudentgrade($studid){
$q = "select * from studentsubject where studid=$studid LIMIT 0,1";
$data = "";
$r = mysql_query($q);
while($row = mysql_fetch_array($r)){
$data = $row['prelim'];
}
return $data;
}?>
PHP
<tbody>
<?php $c=1; ?>
<?php foreach($mystudent as $row): ?>
<tr>
<td><?php echo $c; ?></td>
<td class="text-center"><?php echo $row['studid']; ?></td>
<td class="text-center"><?php echo $row['lname'].', '.$row['fname']; ?></td>
<td class="text-center"><?php echo $grade = $student->getstudentgrade($row['studid']);?></td>
</tr>
<?php $c++; ?>
<?php endforeach; ?>
<?php if(!$mystudent): ?>
<tr>
<td colspan="8" class="text-center text-danger">
<strong>*** No Result ***</strong>
</td>
</tr>
<?php endif; ?>
</tbody>