PHP: While and For Loops

Tutorial on how to use the while and for loops of PHP.

2710 views

Edited: 2019-09-11 16:08

PHP article image

While and For loops can be useful for a variety of tasks, one of which is to generate content automatically. For instance, the navigation links on a website can be generated using a simple loop.

Typically, loops will continue running until a given condition has been met. It can, however, be difficult to create very long loops, depending on your server configuration. Many servers have a maximum execution time, after which the script will be stopped, regardless if it has finished or not.

A simple while loop is shown below:

$number = '1';

while ($number = '1') {
 echo 'Repeating this Forever';
}

While Loop

The below will continue for as long as $number is equal to 1.

The while loop syntax is: while (condition) {DoStuff}

It will check to see if the condition is met, at the beginning of each run.

$number = '1';

while ($number = '1') {
 echo 'Repeating this Forever';
}

Lets limit the loop to a maximum of 15 runs.

$number = '1';

while ($number <= '15') {
echo 'Run Number:' . $number . "\n";

++$number;
}

The conditions basically says, for as long as $number being less then, or equal to 15, run the loop. The last part ++$number;, will add 1 to $number at the end of each run.

Be sure not to make below mistake:

while ($number <= '15') {
$number = '1';
echo 'Repeating this Forever' . "\n";

++$number;
}

Since it will reset $number each time the loop has executed. Also make sure not to declare variables inside the loop unless its necessary, since doing so will re-declare them each time the loop is executed, and as such slow down your scripts.

For Loop Example:

For loops are difficult for many beginners to learn, one reason might be the "for" which apears confusing. So i ask that you keep in mind the While Loop Example from before, then you will have an easier time understanding the next example.

for ($number = '1'; $number <= '15'; ++$number) {
    echo 'Run Number:' . $number . "\n";
}

The for loop actually uses the same order. However instead of declaring $number before the Loop, and adding 1 to $number inside the "actions list", we simply include those actions in the syntax of the loop.

The for loop Syntax is: for (expr1; expr2; expr3) { DoStuff }

Expr1 is where i declared $number, expr2 can be translated into the "condition" from the while loop, and finally expr3 is the action to be performed after each run, in this case, the addition to $number.

Video

Tell us what you think:

  1. An in-dept look at the use of headings (h1-h6) and sections in HTML pages.
  2. Pagination can be a confusing thing to get right both practically and programmatically. I have put a lot of thought into this subject, and here I am giving you a few of the ideas I have been working with.
  3. The best way to deal with a trailing question mark is probably just to make it a bad request, because it is a very odd thing to find in a request URL.
  4. How to optimize image-loading and automatically include width and height attributes on img elements with PHP.
  5. HTTP headers are not case-sensitive, so we are free to convert them to all-lowercase in our applications.

More in: Web development