Sum up dynamically generated fields - php

Question

I have created a script that populates fields of a table dynamically using php. If you look at the snippet of code below, I have hit a brick wall now that I want to add all $sub_total to create a $total_cost. Not sure if I am explaining this well but any direction would be much appreciated.
// loop through results of database query, displaying them in the table
while($row = mysql_fetch_array( $result )) {
// Calculate hours done per day
$hrs_done = $row['time_out'] - $row['time_in'];
if($hrs_done > $row['con_hr']){$hrs = $hrs_done;}
else{$hrs = $hrs_done;}
// echo out results into a table
echo "<tr>";
echo '<td bgcolor="#FFFFFF">' . $row['date'] . '</td>';
echo '<td bgcolor="#FFFFFF">' . $hrs . '</td>';
echo '<td bgcolor="#FFFFFF">' . $row['rate'] . '</td>';
echo '<td bgcolor="#FFFFFF">'?>
// Multiply hrs by rate to get sub total charge for day
<?php $sub_total = $hrs * $row['rate'];
echo $sub_total ;
?>
<?php '</td>';
echo "</tr>";
}
// close table>
echo "</table>";

Answer 1

First, you should look for tutorials that use mysqli or PDO for database access, as mysql_* functions are deprecated.
Second this problem is as easy as just adding up the subtotal items as you iterate through the loop
$grand_total = 0;
while($row = mysql_fetch_array( $result )) {
// your other code omitted for clarity
$sub_total = $hrs * $row['rate'];
$grand_total += $sub_total;
echo $sub_total ;
// more code
}
echo $grand_total;

Answer 2

If I understand your desired behaviour correctly.
During the loop add each $sub_total to $total_cost and echo this after you've completed the while loop
<?php
$total_cost = 0;
while($row = mysql_fetch_array( $result )) {
$sub_total = $hrs * $row['rate'];
$total_cost += $sub_total;
}
echo "Total cost: " . $total_cost;
?>

Answer 3

Your IF/ELSE block leads to one and the same result in both conditions. Is that the desired result?
On the other hand, I'm not sure, if I understood you correct, but if I did, here's my answer.
Since you want to recieve all the $sub_total, you need all the other vars which have built $sub_total:
They are:
$hrs = $hrs_done = $row['time_out'] - $row['time_in']
$row['rate'];
If you try with the SUM() MySQL function, you will recieve the sum of the mentioned columns:
SELECT sum(time_out) as 'sum_time_out', sum(time_in) as 'sum_time_in', sum(rate) as 'sum_rate' FROM myTable;
$hrs_sum = $hrs_done_sum = $row['sum_time_out'] - $row['sum_time_in'];
$stotal_cost = $hrs)sum * $row['sum_rate'];

Answer 4

Each iteration of the while loop creates a new variable $subtotal that you want to add to your constant variable $total.
so within the loop you can add $subtotal to $total and echo the $total after the while loop exits
while($row = mysql_fetch_array( $result ))
{
// your code
$total = $total + $subtotal; // shorthand is - $total += $subtotal.
}
echo $total;