Building a Pizza: Taking the Order

sub build_order()
 #build the pizza order
 { unless ($newOrderFlag)
    { $greeting="Welcome! Please begin building your pizza order." }
   else
    { $greeting="<H3>Build-a-Pizza</H3>".
		"You may modify or finalize ".
		"your order below." }
   
   $greeting.="<br>Current pizza price: <font color='red'>\$".
              sprintf("%.2f",&calcTotal())."</font>.";   
   print $cgiobject->header;
   print $cgiobject->
   start_html(-title=>'Build-a-Pizza',-bgcolor=>'white');
   print "<H2>$greeting</H2>";
   &output_form;
   print $cgiobject->end_html;
 }

The build_order subroutine controls the output of the order form page, and therefore is responsible for displaying the updated order. First, it tests whether this is the start of a new order or an updated order via the $newOrderFlag variable (not related to the seminal 80's synth pop band). In fact, we'll see later that this flag is actually tied to a hidden form field which is planted in the output page.

The hidden form field is simply a way of storing a value on a page, such that the value is returned to the script when the page is submitted. Hidden form fields are a convenient way of "faking" a memory on the Web -- much like writing down a phone number on a scrap of paper and then recalling that paper later to dial the number -- no actual memorizing was involved.

In this application, when the CGI detects that a new order is being placed, because no parameters were submitted, the newOrderFlag hidden form field is not yet planted in the page. However, once the CGI receives an update submission (parameters are submitted), the newOrderFlag is planted to indicate that this is not a new order.

Returning to build_order, an appropriate greeting is output followed by the current price as calculated by the calcTotal subroutine. We've used the formatted output function sprintf() to format the price into a two-decimal place floating point number, simply to prevent strange results such as "$10.5" where we prefer "$10.50".

At its heart, build_order calls the subroutine output_form which will do most of the work in constructing the content of the Web page.

sub init()
 #define initial values for pizza parameters
 { $name="Your name";
   $address="Where to?";
   $phone="Your phone";
   $deliver="deliver";
   $toppings="pepperoni";
   $size="large";
 }

In case of a new order, the init subroutine defines the initial values for the variables which determine the states of the various form fields.

sub get_state_variables()
 #grab any parameters which were submitted
 { $name=$cgiobject->param("order_name");
   $address=$cgiobject->param("order_address");
   $phone=$cgiobject->param("order_phone");
   $deliver=$cgiobject->param("order_deliver");
   $toppings=$cgiobject->param("order_toppings");
   $size=$cgiobject->param("order_size");
   $newOrderFlag=$cgiobject->param("newOrderFlag");
   $orderComplete=$cgiobject->param("finish")
 }

In case of an updated order, the get_state_variables subroutine employs the param method of the CGI object to retrieve the value of each form field and assigns these values to their respective Perl variables.

Single-Session State Maintenance AKA "Building a Pizza" Scenario
The Perl You Need to Know
Building a Pizza: Calculating Cost