Undefined variable during mysql to mysqli conversion - php

Question

I am in the process of converting my old PHP from mysql to mysqli and am running into this error during my conversion. The code worked without throwing errors under mysql but for some reason I get the 'Undefined variable: prevcat in /xx/xx/xx/xx/xx/xx/vluchtbijtoestel.php on line 102' error now. I've tried adding $prevcat = $cat to the variables list but that then breaks the code.
My code:
<?php
define('DB_SERVER', "xxx");
define('DB_USER', "xxx");
define('DB_PASSWORD', "xxx");
define('DB_TABLE', "xxx");
// Define your colors for the alternating rows
$color1 = "#F0F8FF";
$color2 = "#FFFFFF";
$row_count = 0;
// The procedural way
$mysqli = mysqli_connect(DB_SERVER, DB_USER, DB_PASSWORD, DB_TABLE);
$mysqli->set_charset("utf8");
$mysqli->set_charset("utf8");
$mysqli->query("SET NAMES 'utf8'");
if (mysqli_connect_errno($mysqli)) {
trigger_error('Database connection failed: ' . mysqli_connect_error(), E_USER_ERROR);
}
$query = "
SELECT vg.gegevenID, lvm.luchtvaartmaatschappij, lvm.sm_logo, vg.vertrekdatum2, vg.vertrekluchthaven, vg.aankomstluchthaven, vg.toestel, vg.inschrijvingnmr, vlg.vliegtuignaam, vg.vluchtnmr, t.toestel AS toestelnaam, lh.luchthavencode, lh.luchthavennaam, lh.countryflag, lh2.luchthavencode AS aankomstluchthavencode, lh2.countryflag AS countryflagaankomst, vlg.erlr, vlg.firstflight, DATEDIFF(vlg.firstflight,vg.vertrekdatum2) Age1, lh2.luchthavennaam AS aankomstnaam, CONCAT(t.toestel,' ', vlg.erlr) as toestelmeterlr
FROM (tbl_vliegtuiggegevens vlg
INNER JOIN (tbl_luchtvaartmaatschappij lvm INNER JOIN tbl_vluchtgegevens vg ON lvm.luchtvaartmaatschappijID = vg.luchtvaartmaatschappij) ON (vlg.inschrijvingnmr = vg.inschrijvingnmr) AND (vlg.lvmID = lvm.luchtvaartmaatschappijID)) INNER JOIN tbl_toestel t ON vg.toestel = t.toestelID
LEFT JOIN tbl_luchthaven lh
ON vg.vertrekluchthaven = lh.luchthavenID
LEFT JOIN tbl_luchthaven lh2
ON vg.aankomstluchthaven = lh2.luchthavenID
GROUP BY lvm.luchtvaartmaatschappij, toestelmeterlr, vg.inschrijvingnmr, vg.vertrekdatum2
ORDER BY lvm.luchtvaartmaatschappij, toestelmeterlr, vg.vertrekdatum2 DESC, vg.inschrijvingnmr; ";
$result = mysqli_query($mysqli, $query) or trigger_error("Query Failed! SQL: $query - Error: ". mysqli_error($mysqli), E_USER_ERROR);
echo "
<table width='100%' border='0'>
<tr>
<td colspan='3'><strong>Luchtvaartmaatschappij</strong></td>
<td width='17%'> </td>
<td width='12%'> </td>
<td width='19%'> </td>
<td width='28%'> </td>
</tr>
<tr>
<td width='2%'> </td>
<td colspan='3'><strong>Toestel</strong></td>
<td> </td>
<td> </td>
<td> </td>
</tr>
<tr>
<td> </td>
<td width='3%'> </td>
<td width='19%'><strong>vertrekdatum</strong></td>
<td><strong>vliegroute</strong></td>
<td><strong>registratie</strong></td>
<td><strong>vliegtuignaam</strong></td>
<td><strong>vliegtuig leeftijd op reisdatum</strong></td>
</tr>
</table>
";
if($result) {
while($row = mysqli_fetch_assoc($result)) {
$row_color = ($row_count % 2) ? $color1 : $color2;
$date1 = date_create($row['firstflight']);
$date2 = date_create($row['vertrekdatum2']);
$interval = date_diff($date1, $date2);
$cat = $row['luchtvaartmaatschappij'];
$subcat = $row['toestelmeterlr'];
$item = $row['inschrijvingnmr'];
if($cat != $prevcat){
echo " <table width='100%' border='0'>";
echo " <tr>";
echo " <td><br /><hr></td>";
echo " </tr>";
echo " <tr>";
echo " <td><strong><span class='style4'><img src='http://globe-trekking.com/vg/img/logos/sm/".$row['sm_logo']."'> " .$cat. "</strong></span> <br /></td>";
echo " </tr>";
echo "</table>";
echo '<span style="color: #0A0094; font-size: 16px;"> '. $subcat.'</span><br />';//if the category has changed, we also want to show the new subcat
}elseif($subcat != $prevsubcat){
echo '<br /><span style="color: #0A0094; font-size: 16px;"> ' .$subcat.'</span><br />';
}
echo " <table width='1093' border='0' cellspacing='0'>";
echo " <tr>";
echo " <td width='75'> </td>";
echo " <td width='200' bgcolor='$row_color'>" .date("d-M-Y H:i", strtotime($row['vertrekdatum2']))."</td>";
echo " <td width='70' bgcolor='$row_color'><img src='http://globe-trekking.com/vg/img/flags/".$row['countryflag']."'> <abbr title=\"".htmlspecialchars($row['luchthavennaam'])."\">".$row['luchthavencode']."</abbr></td>";
echo " <td width='70' bgcolor='$row_color'> naar </td>";
echo " <td width='130' bgcolor='$row_color'><img src='http://globe-trekking.com/vg/img/flags/".$row['countryflagaankomst']."'> <abbr title=\"".htmlspecialchars($row['aankomstnaam'])."\">".$row['aankomstluchthavencode']."</abbr></td>";
echo " <td width='150' bgcolor='$row_color'>".$row['inschrijvingnmr']."</td>";
echo " <td width='250' bgcolor='$row_color'>".$row['vliegtuignaam'] ."</td>";
echo " <td width='250' bgcolor='$row_color'>" . $interval->y . " jaar en " . $interval->m." maanden </td>";
echo " </tr>";
echo "</table>";
$prevcat = $cat;
$prevsubcat = $subcat;
// Add 1 to the row count
$row_count++;
}
}
mysqli_close($mysqli);
?>

Answer 1

put your code .. you are using $precat and $prevsubcat in your if conditions before declaring and defining it.
$prevcat = $cat;
$prevsubcat = $subcat;
after
$cat = $row['luchtvaartmaatschappij'];
$subcat = $row['toestelmeterlr'];
like this
$cat = $row['luchtvaartmaatschappij'];
$subcat = $row['toestelmeterlr'];
$prevcat = $cat;
$prevsubcat = $subcat;

Answer 2

Put
$prevcat = '';
$prevsubcat = '';
Juste before "While" expression
Regards