PHP 101 (part 3) - Chocolate Fudge And Time Machines - Back To The Future (
Page 2 of 9 )
For those of you unfamiliar with the term, a loop is a control
structure which enables you to repeat the same set of PHP statements or commands
over and over again; the actual number of repetitions may be dependent on a number
you specify, or on the fulfillment of a certain condition or set of conditions.
The first - and simplest - loop to learn in PHP is the so-called "while" loop,
which looks like this:
while (condition)
{
do this!
}
or, in English,
while (it's raining)
{
carry an umbrella!
}
In this case, so long as the condition specified evaluates as true - remember
what you learned last time? - the PHP statements within the curly braces will
continue to execute. As soon as the condition becomes false - the sun comes out,
for example - the loop will be broken and the statements following it will be
executed.
Here's a quick example which demonstrates the "while" loop:
<?
// if form has not been submitted, display initial page
if (!$submit)
{
?>
<html>
<head>
</head>
<body>
<h2>The
Incredible Amazing Fantabulous Time Machine</h2>
<form action="tmachine.php4"
method="POST">
Which year would you like to visit?
<input type="text" name="year"
size="4" maxlength="4">
<input type="submit" name="submit" value="Go">
</form>
</body>
</html>
<?
}
else
//
else process it and generate a new page
{
?>
<html>
<head>
</head>
<body>
<?
//
current year
$current = 2000;
// check for dates in future and generate appropriate
message
if ($year > $current)
{
echo "<h2>Oops!</h2>";
echo "Sorry,
this
time machine can only travel backwards at the moment.
But leave your phone
number
and we'll call you when the new improved model
goes on sale.";
}
else
{
// or
echo "<b>Going back to $year...</b><br>";
// use a while loop
to print
a series of numbers (years)
// until the desired number (year) is reached
while($year
< $current)
{
$current = $current - 1;
echo "$current ";
}
echo "<br><b>The
past definitely isn't all it's cracked up to be!</b>";
}
?>
</body>
</html>
<?
}
?>
In this case, we first ask the user for the year he'd like to visit - this year
is stored as the variable $year, and passed to the PHP script. The script first
checks the year to ensure that it in the past [hey, we're working on it!] and
then uses a "while" loop to count backwards from the current year - 2000, stored
in the variable $current - until the values of $current and $year are equal.
Note our usage of the $submit variable to use the same PHP page to generate both
the initial form and the subsequent pages - we explained this technique in detail
last time.
/ 5 
