One of the simplest and most popular add-ons to a Web site is anonline poll, allowing visitors to vote on hot-button issues. In thisarticle, find out how PHP can be used to build a powerful, good-lookingonline poll for your Web site, and also learn a little bit about its imageand cookie manipulation functions.
So that takes care of the mechanics of displaying a question, registering votes, and displaying totals. The next item to address is the stated requirement to be able to view previous polls. In this application, the script to accomplish this is called "archive.php".
"archive.php" is extremely simple. It connects to the database, queries for a list of all available polls and votes, and then uses a "while" loop to iterate through the result set and display the final tally for each poll. Take a look:
<html>
<head>
<basefont face="Arial">
</head>
<body bgcolor="white">
<?
// includes
include("config.php");
include("common.php");
// connect and get a list of previous questions
$connection = mysql_connect($hostname, $user, $pass) or die ("Unable to
connect!");
$query = "SELECT question, response1, response2, response3, votes1, votes2,
votes3, date from $table";
$result = mysql_db_query($database, $query, $connection) or die ("Could not
execute query: $query. " . mysql_error());
// iterate through resultset
while(list($question, $response1, $response2, $response3, $votes1,
$votes2, $votes3, $date) = mysql_fetch_row($result))
{
// calculate the total votes
$total = $votes1 + $votes2 + $votes3;
if ($total > 0)
{
// convert sub-totals into percentages
$perc_votes1 = round(($votes1/$total)*100,2);
$perc_votes2 = round(($votes2/$total)*100,2);
$perc_votes3 = round(($votes3/$total)*100,2);
}
// no votes yet - can cause "division by zero" errors
else
{
$perc_votes1 = $votes1;
$perc_votes2 = $votes2;
$perc_votes3 = $votes3;
}
// print a table with results
echo "<table border=0 cellspacing=0 cellpadding=5>";
echo "<tr><td colspan=3><b>$question</b></td></tr>";
// and a graph
echo "<tr><td>$response1</td><td> $votes1 ($perc_votes1%)</td><td
rowspan=4 valign=top><img
src=graph.php?votes1=$votes1&votes2=$votes2&votes3=$votes3
border=0></td></tr>";
echo "<tr><td>$response2</td><td> $votes2 ($perc_votes2%)</td></tr>";
echo "<tr><td>$response3</td><td> $votes3 ($perc_votes3%)</td></tr>";
echo "<tr><td><font size=-2>Posted on " . fixDate($date) .
"</font></td><td><font size=-2>$total total votes</font></td></tr>";
echo "</table><p>";
}
// close connection
mysql_close($connection);
?>
<p>
<font size="-2"><a href="start.php">back to main page</a></font>
</body>
</html>
In this case, I've checked that the total number of votes
is greater than zero before calculating percentages, to avoid "division by zero" errors - this is the correction I mentioned a few pages back.
Here's what it looks like:
There's one more thing I'd like to do before leaving "archive.php" - modify it so that, in addition to displaying a complete list of previous polls and results, it also has the capability to display the results of any single, specified poll. This comes in handy on my first page, since it allows me to offer my users a couple of additional options before they cast their vote.
<!-- from start.php -->
<font size=-2><a href="archive.php?id=<? echo $id; ?>">view
results</a></font>
<font size=-2><a href="archive.php">view past polls</a></font>
If "archive.php" is called without any parameters, it
should display the complete archive; if called with a specific $id identifier, it should only display results for that specific poll question.
This is pretty easy to accomplish - I just need to inject the following code snippet into the script:
<?
// archive.php
$query = "SELECT question, response1, response2, response3, votes1, votes2,
votes3, date from $table";
// if a specific id is requested, modify query to only return that question
if ($id)
{
$query .= " WHERE id = $id";
}
$result = mysql_db_query($database, $query, $connection) or die ("Could not
execute query: $query. " . mysql_error());
?>
This article copyright Melonfire 2001. All rights reserved.{mospagebreak title=One Picture, A Thousand Words} Both "archive.php" and "vote.php" rely on a dynamically-generated bar graph to spiff up the page design. And this dynamically-generated graph is created through the magic of PHP's image generation functions, as embodied in the file "graph.php".
If you take a close look at the scripts above, you'll see that "graph.php" is always passed a few variables via the URL GET method; these variables represent the number of votes for each of the three available options. The function of "graph.php" thus becomes to calculate appropriate percentages for each of these options, and represent these percentages graphically. Let's take a look:
<?
// graph.php - generates a bar graph of votes using an existing, blank image
// calculate the total
$total = $votes1 + $votes2 + $votes3;
if ($total > 0)
{
// convert sub-totals into percentages
$perc_votes1 = round(($votes1/$total)*100,2);
$perc_votes2 = round(($votes2/$total)*100,2);
$perc_votes3 = round(($votes3/$total)*100,2);
}
// "division by zero" correction
else
{
$perc_votes1 = $votes1;
$perc_votes2 = $votes2;
$perc_votes3 = $votes3;
}
// header
Header("Content-Type: image/jpeg");
// set up image and colours
$im = ImageCreateFromJPEG("graph.jpg");
$blue = ImageColorAllocate($im, 8, 63, 206);
// fill with colour up to specific length
// length of colour bar depends on percentage of votes
ImageFilledRectangle($im, 0, 3, ($perc_votes1*2), 9, $blue);
ImageFilledRectangle($im, 0, 34, ($perc_votes2*2), 40, $blue);
ImageFilledRectangle($im, 0, 65, ($perc_votes3*2), 71, $blue);
// output to browser
ImageJPEG($im);
?>
The first few lines are familiar - the conversion of
absolute numbers into percentages.
<?
// calculate the total
$total = $votes1 + $votes2 + $votes3;
if ($total > 0)
{
// convert sub-totals into percentages
$perc_votes1 = round(($votes1/$total)*100,2);
$perc_votes2 = round(($votes2/$total)*100,2);
$perc_votes3 = round(($votes3/$total)*100,2);
}
// "division by zero" correction
else
{
$perc_votes1 = $votes1;
$perc_votes2 = $votes2;
$perc_votes3 = $votes3;
}
?>
Once that's done with, a header is sent and a base image,
"graph.jpg", read into memory. This is the base image for all graphs to be generated, and it looks like this:
The length of each empty bar in the image above is 200 pixels (100%). Now, based on the percentage values already generated, "graph.php" will fill each bar with a specified colour; the length of the fill is determined by the quantum of votes. For example, if a specific option receives 25% of the votes, the fill will be 50 pixels long (25% of 200).
<?
// fill with colour up to specific length
// length of colour bar depends on percentage of votes
ImageFilledRectangle($im, 0, 3, ($perc_votes1*2), 9, $blue);
ImageFilledRectangle($im, 0, 34, ($perc_votes2*2), 40, $blue);
ImageFilledRectangle($im, 0, 65, ($perc_votes3*2), 71, $blue);
?>
Once the bars are filled, the image is sent to the
browser for display.
<?
// output to browser
ImageJPEG($im);
?>
Here's an example of what it might look like. In case this didn't make any sense, you should take a look at the article entitled "Image Generation With PHP" at http://www.devshed.com/Server_Side/PHP/ImageGeneration/. And after you're done with that, come back here and experiment with displaying poll results in the form of a pie chart, rather than a bar graph. Go on - it isn't nearly as hard as it looks!
This article copyright Melonfire 2001. All rights reserved.
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