PHP: Loops
Category: Advanced
Prologue
PHP: Main has a big amount of Tutorials.
Hopefully this one will be a nice add.
I really do also hope that you will understand all the three loops which PHP have and which are explained here.
We'll not go the most advanced part, dealing with break and continue, but I will show you some nice tricks which are quite advanced - so be sure to already know some stuff beforing entering to loops.
You can learn basics from other Tutorials. Check out PHP: Main !
a tip before starting
you can really screw your server and browser for some period if you run a infinite loop.
So, before proceeding, put this before your loop:
<?
set_time_limit(5);
?>
That will exit the script if it runs more than 5 seconds.
while
while loops are known as the easiest loops in PHP.
Unlike their sister loops, do...while, which I will explain later, they keep outputing every time a value is true.
My First While Loop
You must do:
-set up a variable with a number
-set up a expression for while, thus:
while ($int [Comparison Operator] $max)
And while will run as long as $int it is smaler than $max.
Generally.
This can be changed by changing the Comparison Operator.
- in the loop, you must specify a $int++ to avoid infite loop.
<?
$num = 1;
// $max is 10
while ($num <= 10) {
echo "This is a message No. $num. <br /> \n";
$num++;
}
?>
Outputes:
This is a message No. 1.
This is a message No. 2.
This is a message No. 3.
This is a message No. 4.
This is a message No. 5.
This is a message No. 6.
This is a message No. 7.
This is a message No. 8.
This is a message No. 9.
This is a message No. 10.
Easy, huh?
do...while
This actually isn't a stand-alone loop.
It is basically a while loop, but implemented with do 'loop'.
Regular while and do...while loops are same, except for one thing: do...while will, unlike while execute at least once, even if the condition is at beggining false.
do...while syntax
<?
do {
// the actions which run while the loop's condition is true
} while ( condition )
?>
foreach
foreach loops are used for array, only.
With them, you can get all the values from a array. Both indexes and keys.
This loops are similar to implode() function.
Example 1 - my first foreach loop
Situation: we have the content of our fridge put onto a array.
Now we must export that array into a document.
<?
$fridge = array('banana', 'lettuce', 'carrot', 'eggs', 'tomatos', 'milk');
foreach ($fridge as $contents) {
echo "We have $contents. <br /> \n";
}
?>
Output:
We have banana.
We have lettuce.
We have carrot.
We have eggs.
We have tomatos.
We have milk.
Example 2 - getting contents and their index
Situation: same, except that we will now also tell the index of our content.
<?
$fridge = array('banana', 'lettuce', 'carrot', 'eggs', 'tomatos', 'milk');
foreach ($fridge as $indexes => $contents) {
echo "At position $indexes we have $contents. <br /> \n";
}
?>
Output:
At position 0 we have banana.
At position 1 we have lettuce.
At position 2 we have carrot.
At position 3 we have eggs.
At position 4 we have tomatos.
At position 5 we have milk.
'Index' is a position of array's content.
It can be set. If it is not set, it will be a number, the number of that property's position in array.
Example 3 - where / what
Situation: we must output where is something. Like telling a story.
This example will be used so you can better understand indexes.
<?
$a = array('hawaii' => 'nice', 'croatia' => 'hot', 'antartica' => 'cold', 'usa' => 'mild');
foreach ($a as $where => $what) {
echo "In $where is $what. <br /> \n";
}
?>
Outputes:
In hawaii is nice.
In croatia is hot.
In antartica is cold.
In usa is mild.
for
Now I'll scare you!
This words coming from php.net:
for loops are the most complex loops in PHP.
Have enough strength to confront this?
Lets go!
Syntax
The syntax of for is thus:
for ($int; $max; $what)
$int = you initialize a number here. Lets say you set $int to 1.
$max = the number which will be reached, and then the loop will exit. Lets set it to 10.
$what = ++ or --. ++ is increment and -- is decrement. You will almost always set it to ++. We'll set this to ++ now.
Note that I put those variables like so just to explain nicer. $int, $max and $what must have the same variable name (i.e. $i).
So it would go now:
<?
for ($i = 1; $i<=10; $i++) {
echo "My first for loop. <br /> \n";
}
?>
Outputes:
(you would be surprised how a small amount of PHP code can generate big output!)
My first for loop.
My first for loop.
My first for loop.
My first for loop.
My first for loop.
My first for loop.
My first for loop.
My first for loop.
My first for loop.
My first for loop.
Or vica-versa, with decrementing
<?
for ($i=10; $i>=0; $i--) {
echo '$i = ' . $i . '<br /> \n';
}
?>
Outputes:
$i = 10
$i = 9
$i = 8
$i = 7
$i = 6
$i = 5
$i = 4
$i = 3
$i = 2
$i = 1
$i = 0
Something Useful
-outputting random NG BBS Forum with for and next combination.
<?
$a = array('General', 'Where is/How to?', 'Flash', 'Politics', 'Programming', 'Clubs & Crews', 'Audio');
for ($i = 1; $i<=rand(0, count($a)-1); $i++) {
next($a);
}
echo current($a);
?>
You do now realize that for isn't so hard right?
I really thinks it is not.
Buy Buy
-Nino
