Today we started with this exercise: 

Write a CGI program in Python that can update a counter at 
the user's request. The counter goes up and down by one. The 
basic outline of the interface is like this: 


   +---------------------------------------+
   |   The counter is now: ..........      |
   |                                       |
   |   Press [here] to go up.              | 
   |                                       |
   |   Press [here] to go down.            |
   +---------------------------------------+


The first [here] is a link, the second is a button. 

Here's what we developed in class:

!/usr/bin/python

import cgi

print "Content-type: text/html\n\n"

(counter, message, action) = ("", "", "")

d = cgi.FieldStorage()

if d.has_key("counter"): counter = d["counter"].value
if d.has_key("message"): message = d["message"].value
if d.has_key("action"):  action  = d["action"].value

if message:
  if action == "up":
    counter = str(int(counter) + 1)
  else:
    counter = str(int(counter) - 1)
  message = "Your new counter value is: " + counter
else:
  counter = 0
  message = "Welcome, your counter is: " + str(counter)

print """
<form>
  %s <p>

  Press <a href="?action=up&counter=%s&message=%s">here</a> to go up. <p>

  Press <input type="submit" name="action" value="here"> to go down.

  <input type=hidden name=counter value="%s">
  <input type=hidden name=message value="%s">
</form>
""" % (message, counter, message, counter, message)

Introduction to PHP

We briefly stated how PHP works, then we converted this program to PHP: 



<?
  if ($message) {
    if ($action == "up") {
      $counter = $counter + 1;
    } else {
      $counter = $counter - 1;
    }
    $message = "Your new counter value is: " . $counter;
  } else {
    $counter = 0;
    $message = "Welcome, your counter is: " . $counter;
  }
?>

<form>
  <?=$message?> <p>

  Press <a href="?action=up&counter=<?=$counter?>&message=<?=$message?>">here</a> to go up. <p>

  Press <input type="submit" name="action" value="here"> to go down.

  <input type=hidden name=counter value="<?=$counter?>">
  <input type=hidden name=message value="<?=$message?>">
</form>