Conversion of units of area

Control Statements example from a Well House Consultants training course
More on Control Statements [link]

This example is described in the following article(s):
• Hot answers in PHP - [link]

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Source code: units.php Module: H104


<?php

// Convert area units

$data = <<<INFO
# Area Unit conversions

# define base units

1, square millimetres

# define each unit in relation to a previously defined one

1, square centimetres, 100, square millimetres
1, square metres, 10000, square centimetres
1, hectares, 10000, square metres
1, square kilometers, 100, hectares

1, square inches, 645.16, square millimetres
1, square feet, 144, square inches
1, square yards, 9, square feet
1, acres, 4840, square yards
1, square miles, 640, acres
1, townships, 36, square miles

10, square chains, 1, acres
160, square rods, 1, acres
INFO;

$optlist = "";
foreach (explode("\n",$data) as $line) {
        list($du,$dn,$bu,$bn) = explode(", ",$line);
        if (ereg('^[[:space:]]*#',$du)) continue;
        if (ereg('^[[:space:]]*$',$du)) continue;
        if (! $bu) {
                $utable[$dn] = $du;
                $ultbase = $dn;
        } else {
                $utable[$dn] = 1.0 * $utable[$bn] * $bu / $du;
        }
        $optlist .= "<option value='$dn'>$dn";
        # print $line."<br>";
        # print "defining $dn as $utable[$dn] $ultbase<br>";
        }
$ulist = implode(", ",array_keys($utable));
if ($invert = $utable[$_REQUEST[units]]) {
        $result = "<em>$_REQUEST[amount] $_REQUEST[units] converts to</em><br>";
        $base = 1.0 * $_REQUEST[amount] * $invert;
        foreach (array_keys($utable) as $uname) {
                $newval = $base / $utable[$uname];
                if ($newval > 0.0001 and $newval < 10000.0)
                        $result .= "$newval $uname<br>";
        }
} else {
        $result = "Results appear here when you submit the form<br>";
}
?>
<html>
<head><title>Area Unit Conversion</title></head>
<body><h1>Area Conversions</h1>
<form>Please convert <input name=amount>
<select name=units> <?= $optlist ?> </select>
<input type=submit value=now> to alternative units</form>
<hr>
<?= $result ?>
<hr>
This program knows about the following units: <?= $ulist ?>. It only report
on reasonable alternative units - it won't report conversions that result in
very tiny or very large numeric values.
<hr>
Program written in PHP by <a href=http://www.wellho.net>Well House Consultants</a>, &copy; <?= date("Y") ?><br>
We offer <a href=/course/php.html>training courses in PHP</a> if you want to learn!<br>
Or here's the source of the program if you can already work with PHP:<br><br>
<?= highlight_file($_SERVER[PATH_TRANSLATED]); ?>
<hr>
</body>
</html>

Learn about this subject

This module and example are covered on the following public courses:
* Learning to program in PHP
* PHP Programming
* Beginning PHP - weekend course / hobby / club / leisure users
* PHP Programming
* Learning to program in PHP
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