LOOPS
By Stephon Unomon
We all have mundane, repetitive tasks
we have to do. You know, like putting stamps on all those holiday greeting
cards we send out every year? Well, from a programming angle, PHP can help us
ease the workload on repetitive tasks in websites with a LOOP.
The first one we’ll discuss is the WHILE LOOP. It sounds like a weird carnival ride (I got sick on the
While Loop - it was great!) but it is one of the most useful loop functions in
PHP.
Logically, it looks like this:
while (
this conditional statement is true){
//do this;
}
This isn’t real code - just an illustration of how it works.
now, here’s what happens, step by step:
1. PHP checks the
conditional statement. If it is true, move to step 2. If it is false, go to
step 4.
2. PHP runs the
code contained in the loop.
3. We go back to
step 1 and start again, making a LOOP.
4. Once the
conditional statement becomes false, the loop exits, and code placed after the
loop runs.
Real World Usage for
WHILE LOOPS
The Creamy Bagel Company wants to
show a pricing matrix on their website for up to a 20 bagel pack. But, since
bagels are a valuable commodity, the price fluctuates regularly. You have to
change it. You love your job.
Using a While Loop and some HTML, this can happen with relative
ease, and you’ll only have to change one
value when the bagel price changes (then charge for 3 hours of work!).
Read on...
<?php
$bagel_price = 2.15; //This is the price of one bagel
$counter = 1;
echo "<table border=\"1\"
align=\"center\">"; //note the escapes for quotes!
echo
"<tr><th>Quantity</th>";
echo "<th>Price</th></tr>";
while ( $counter <= 20 )
{ //we just set the counter limit at 20
echo "<tr><td>";
echo $counter;
echo "</td><td>";
echo $bagel_price * $counter; //here we multiply
echo "</td></tr>";
$counter = $counter + 1; //here we add 1 to the
counter and start again
}
echo "</table>";
?>
Our actual Loop code is highlighted in blue above. You’ll
see that we set the variables $bagel_price and $counter. The $counter variable
allows us to create a math function to increment the unit price by 1 each time
we loop (see the $counter = $counter + 1 part at the bottom of the loop?)
So, while $counter equals less-than-or-equal-to 20, this
loop will function. Once we hit 21, that’s it - no more loop!
+ addition (You can use ++ to increment a
value by 1)
- subtraction
* multiplication
/ division
|
Here’s what it looks like in a browser...and you can see
at-a-glance what 13 bagels will cost you!
The FOR LOOP
The FOR LOOP is very similar to a
WHILE LOOP. The difference being a little bit more code is contained in the
loop. The FOR LOOP can be a little more compact than a WHILE LOOP. Here’s the
logic:
for ( create a counter; conditional statement; increment
the counter){
do
this;
}
Let’s use our fluctuating bagel cost from above and write
this out. Oops - bagels just went up 10 cents!
<?php
$bagel_price = 2.25;
echo "<table border=\"1\"
align=\"center\">";
echo "<tr><th>Qu
antity</th>";
echo "<th>Price</th></tr>";
for ( $counter = 1; $counter
<= 20; $counter += 1) {
echo "<tr><td>";
echo $counter;
echo "</td><td>";
echo $bagel_price * $counter;
echo "</td></tr>";
}
echo "</table>";
?>
Once again, the loop is highlighted in blue. You’ll notice
that the counter is defined inside the loop as opposed to a variable outside.
And..to the right, you’ll see the output.
There’s one more Loop we’re going to cover, isn’t this
exciting? Hello? Still there?
The FOR EACH Loop
What if you want to loop through an
Associative Array? (See? Told you we’d get back to this!) You can use FOR EACH
to do this task. Where the WHILE and FOR loops run until an error is
encountered, the FOR EACH loop will run through every element in the array.
Let’s revisit the associative array we set up with the
trucks...
<?php
$truck[“Toyota”] = Tundra;
$truck[“Nissan”] = Titan;
$truck[“Dodge”] = Ram;
?>
To loop through the Makers / Models, we’d use this code:
<?php
forea
ch( $truck as
$make => $model){
echo
"Make: $make, Model: $model <br />";
}
?>
The code is written in a strange way, it isn’t obvious how
it works. Let’s look at it in a simpler way:
$something as $key => $value
So, in english...
FOR each thing in the array, I want to refer to the key as $key and the value as $value. The operator ‘=>’ indicates the relationship
between the key and the value...the key “points” to the value.
I think that’s about all we need to cover with Loops.
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