Calculating total - php

Question

I'm looking for some help on calculating a total from lots of subtotals from a database, the code I'm using is working to calculate it, but the PHP echos an error saying that
Notice: Undefined variable: tot in ..............\viewing.php on line 192
But it is still calculating the total cost and echoing it, any ideas on how to get rid of that error?
I am getting the subtotals from a database using this:
while($row=mysql_fetch_array($result)) {
echo .....
$tot += $row['subtotal'];
}
At the bottom of the page, I've made it so it shows the total and its working, but its still giving me an error saying that the variable tot is undefined, any ideas?

Answer 1

It isn't an error, it's a notice!
Initialise
$tot = 0;
before your while loop

Answer 2

You need to define your $tot variable
Put this before using it in your loop
$tot = 0;

Answer 3

$tot = 0;
while($row=mysql_fetch_array($result)) {
echo .....
$tot += $row['subtotal'];
}
echo $tot;

Answer 4

From the php documentation:
It is not necessary to initialize variables in PHP however it is a
very good practice.
However it also says:
Relying on the default value of an uninitialized variable is
problematic in the case of including one file into another which uses
the same variable name. It is also a major security risk with
register_globals turned on. E_NOTICE level error is issued in case
of working with uninitialized variables..
You can turn off notices at a variable level by doing this:
while($row=mysql_fetch_array($result)) {
#$tot += $row['subtotal'];
}
Having said that best practice is:
$tot = 0;
while($row=mysql_fetch_array($result)) {
$tot += $row['subtotal'];
}