Form Calculations
In this tutorial you will be learning the following:
- assigning variables
- operators
- outputting info
You should have completed these tutorials:
PHP Form and
Order Processing in this series.
1. Open up your processingorder.php. We need to first assign your
variables a value that will set the variable type. Set the number value set
of $totalqty to a whole number, and set the number value set of $totalamount
to a real number by typing the followingJust above the end of the script tag
(?>):
$totalqty = 0;
$totalamount = 0.00;
Set the initial values for the price of tires, oil and sparkplugs. The
constants are always typed in all capitals by
typing in the following:
define("TIREPRICE", 100);
define("OILPRICE", 10);
define("SPARKPLUGPRICE", 4);
2. Inside your PHP script just above the ?> we want to add our
calculations. First set $totalqty equal to the sum of each of the
quantities, that is, $totalqty = $tireqty + $oilqty + $sparkplugqty; .
<?
echo "<P>Order Processed.";
echo date("H:i, jS F");
echo "<br>";
echo $tireqty." tires<BR>";
echo $oilqty." bottles of oil<BR>";
echo $sparkplugqty." spark plugs<BR>";
$totalqty = 0;
$totalamount = 0.00;
define("TIREPRICE", 100);
define("OILPRICE", 10);
define("SPARKPLUGPRICE", 4);
$totalqty = $tireqty + $oilqty + $sparkplugqty;
?>
3. Knowing the quantities of each item, we can multiply them by a SET
price or CONSTANT. All constants are written without the $ and are written
in capital letters. The left side of the equation is set equal to the right
side, in this case, the right side will calculate the price for each item,
tires, oil, and sparkplugs and add them together. It can be calculated by
the following
Total price = (tire quantity X tire price)
+ (oil quantity X oil price) + (sparkplug quantity X SPprice)
To write this in PHP we have to use PHP formatting with the variables and
constant(prices) we set. We can rely on PHP to always do all mutiplication
and division pior to addition so we drop quotes. The multiplication symbol
is an * and addition +. So we place the following:
$totalamount = $tireqty * TIREPRICE
+ $oilqty * OILPRICE
+ $sparkplugqty * SPARKPLUGPRICE;
In our order processing script page our script should now look like this:
<?
echo "<P>Order Processed.";
echo date("H:i, jS F");
echo "<br>";
echo $tireqty." tires<BR>";
echo $oilqty." bottles of oil<BR>";
echo $sparkplugqty." spark plugs<BR>";
$totalqty = 0;
$totalamount = 0.00;
define("TIREPRICE", 100);
define("OILPRICE", 10);
define("SPARKPLUGPRICE", 4);
$totalqty = $tireqty + $oilqty + $sparkplugqty;
$totalamount = $tireqty * TIREPRICE
+ $oilqty * OILPRICE
+ $sparkplugqty * SPARKPLUGPRICE;
?>
4. We need to format the number that will be calculated so that it is
in 2 decimal places, representing cents. To do this we can take the
newly calculated $totalamount and apply a number_format command set at 2
decimal places.
<?
echo "<P>Order Processed.";
echo date("H:i, jS F");
echo "<br>";
echo $tireqty." tires<BR>";
echo $oilqty." bottles of oil<BR>";
echo $sparkplugqty." spark plugs<BR>";
$totalqty = 0;
$totalamount = 0.00;
define("TIREPRICE", 100);
define("OILPRICE", 10);
define("SPARKPLUGPRICE", 4);
$totalqty = $tireqty + $oilqty + $sparkplugqty;
$totalamount = $tireqty * TIREPRICE
+ $oilqty * OILPRICE
+ $sparkplugqty * SPARKPLUGPRICE;
$totalamount = number_format($totalamount, 2);
?>
To those not used to programming, they may wonder why we can set $totalamount
to $totalamout. Remember, that the variable on the left is being reset
by the calculation on the right side.
5. Outputting this data to your order processing page that the user will
see involves the user of the echo command (see
the second tutorial here.)
First add a line break:
echo "<BR>\n";
Add a line that gives you the total number of items ordered. First
label what it is, Items ordered, then use the period to concatenate the
variable after it. Follow this with a line break.
echo "Items
ordered:
".$totalqty."<br>\n;
Add a line that gives you the total cost of the order, and space the
total cost so the items line up in a browser. Then add a period to
concatenate the variable value, followed by a long break.
echo
"Subtotal:
".$totalamount."<BR>"\n;
Define the tax rate at 10% by setting the variable, no echo here. 10 %
is equal to 10 cents on a dollar, so the rate will be 0.10.
$taxrate = 0.10; // local sales tax is 10% here
Calculate the total amount as 110%(1+the tax rate) of the previously
calculated varable. This will be your total including the 10%tax.
$totalamount
= $totalamount * (1+$taxrate);
You will then need to format the text to 2 decimal places.
$totalamount = number_format($totalamount, 2);
You will then need to give the total including tax.
echo "total Including Tax: $".$totalamount."<BR>\n";
6. So far your total script page looks like this:
<?
echo "<P>Order Processed.";
echo date("H:i, jS F");
echo "<br>";
echo $tireqty." tires<BR>";
echo $oilqty." bottles of oil<BR>";
echo $sparkplugqty." spark plugs<BR>";
$totalqty = 0;
$totalamount = 0.00;
define("TIREPRICE", 100);
define("OILPRICE", 10);
define("SPARKPLUGPRICE", 4);
$totalqty = $tireqty + $oilqty + $sparkplugqty;
$totalamount = $tireqty * TIREPRICE
+ $oilqty * OILPRICE
+ $sparkplugqty * SPARKPLUGPRICE;
$totalamount = number_format($totalamount, 2);
echo "<BR>\n";
echo "Items
ordered:
".$totalqty."<br>\n;
echo
"Subtotal:
".$totalamount."<BR>"\n;
$taxrate = 0.10; // local sales tax is 10% here
$totalamount
= $totalamount * (1+$taxrate);
$totalamount = number_format($totalamount, 2);
echo "total Including Tax: $".$totalamount."<BR>\n";
?>
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