Why aren't the variables storing? - php

Question

Okay, as you can see in the code I'm trying to add the total up.. I have used a variable outside a while() before, but not this way. So if someone could point me in the right direction? I know what I need to make the form work, that's not the problem. My formatting is bad, but that's not the problem either so please no comments on it.
<?php
require 'core/config.php';
?>
<form onsubmit="sendToServer();">
CPU <select id="proc">
<?php
$cpuPrice = "";
$query = $con->query("SELECT * FROM partslist WHERE Category = 'CPU'");
while($row = $query->fetch_array(MYSQLI_BOTH))
{
$cpuPrice .= $row['ProductPrice'];
echo '<option value="'.$row['ProductName'].'">'.$row['ProductName'].' - '.$row['ProductPrice'].'</option>';
}
?>
</select><br>
RAM <select id="proc1">
<?php
$ramPrice = "";
$query = $con->query("SELECT * FROM partslist WHERE Category = 'RAM'");
while($row = $query->fetch_array(MYSQLI_BOTH))
{
$ramPrice .= $row['ProductPrice'];
echo '<option value="'.$row['ProductName'].'">'.$row['ProductName'].' - '.$row['ProductPrice'].'</option>';
}
?>
</select><br>
GPU <select id="proc2">
<?php
$gpuPrice = "";
$query = $con->query("SELECT * FROM partslist WHERE Category = 'GPU'");
while($row = $query->fetch_array(MYSQLI_BOTH))
{
$gpuPrice .= $row['ProductPrice'];
echo '<option value="'.$row['ProductName'].'">'.$row['ProductName'].' - '.$row['ProductPrice'].'</option>';
}
?>
</select><br>
HDD <select id="proc3">
<?php
$hddPrice = "";
$query = $con->query("SELECT * FROM partslist WHERE Category = 'HDD'");
while($row = $query->fetch_array(MYSQLI_BOTH))
{
$hddPrice .= $row['ProductPrice'];
echo '<option value="'.$row['ProductName'].'">'.$row['ProductName'].' - '.$row['ProductPrice'].'</option>';
}
?>
</select><br>
SSD <select id="proc4">
<?php
$ssdPrice = "";
$query = $con->query("SELECT * FROM partslist WHERE Category = 'SSD'");
while($row = $query->fetch_array(MYSQLI_BOTH))
{
$ssdPrice .= $row['ProductPrice'];
echo '<option value="'.$row['ProductName'].'">'.$row['ProductName'].' - '.$row['ProductPrice'].'</option>';
}
$total = $cpuPrice + $ramPrice + $gpuPrice + $hddPrice + $ssdPrice;
?>
</select><br><br>
<button type="submit">Build</button>
</form>
<div style="border:1px;border-color:black;">Total: $<?php echo $total; ?></div>
Edit - more in depth..
What I need is to display the total, but it's empty..

Answer 1

Try doing the math in the query itself, for example:
CPU <select id="proc">
<?php
$cpuPrice = 0;
$query = $con->query("SELECT *, (SUM(ProductPrice)) as CpuPrice FROM partslist WHERE Category = 'CPU'");
while($row = $query->fetch_array(MYSQLI_BOTH))
{
$cpuPrice = $row['CpuPrice '];
echo '<option value="'.$row['ProductName'].'">'.$row['ProductName'].' - '.$row['ProductPrice'].'</option>';
}
echo 'cpuPrice'.$cpuPrice;
?>
</select><br>