PHP - Variables, Operators and Expressions

PHP module H103

Variables, Operators and Expressions

Exercises, examples and other material relating to training module H103. This topic is presented on public courses Learning to program in PHP, PHP Programming, Beginning PHP - weekend course / hobby / club / leisure users

Writing a straightforward but meaningful executable web page in PHP. You'll learn how to read data from the user via a form, how to perform calculations using operators, and store the results in computer memory using variables. You'll also learn how to include those results in your response page.

Articles and tips on this subject		updated
3917	BODMAS - the order a computer evaluates arithmetic expressions What order does a computer program use to evaluate expressions? If I write 2 + 3 * 4 + 5 does it start off, left to right ... 2 + 3 is 5 5 * 4 is 20 20 + 5 is 25 No! it does not, even though the newcomer might think that was the most natural way for ...	2012-11-10
3916	PHP variables - dynamically typed. What does that mean? When we're programming, we store data in our computer memory in one step of our process, then read it back for further reference or processing in a later step. In the very early days, this was planned out using the numeric location in the computer memory, but very rapidly programming languages ...	2012-11-10
3278	Do I need to initialise variables - programming in C, C++, Perl, PHP, Python, Ruby or Java. Starting with a clean slate. Are variables initisialised, and if so, how? Even with this fundamental question, languages vary considerably. C and C++ From my (e)mailbag ... """In a piece of code we’ve written we declare an array, but we do not fill the elements with values, we assume (dangerous ...	2011-05-05
2215	If nothing, make it nothing. Here's a peculiar PHP statement I wrote this morning: if ($aindex[$chk] == "") $aindex[$chk] = ""; What was I doing? I am actually checking to see whether there's anything in an array element and if there isn't (which could be because it's empty or because it doesn't yet exist), then it ...	2009-06-03
748	Getting rid of variables after you have finished with them If you've finished with a variable in your program, you can usually just leave it "in situe" and it will be destroyed and the memory it occupied will be released when you exit from your program. In many languages, variables within named blocks of code have an even shorter "shelf life" - by default, a ...	2006-06-09
483	Double Dollars in PHP What does this print? <?php $first = "fur"; $last = "feather"; $$first = "yum yum "; ${"$first$last"} = "yikes"; print "$fur $furfeather"; ?> It prints "yum yum yikes". In PHP, you can write a variable name within a variable name, and that's what I've done in this example. The variable called ...	2006-06-05

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Examples from our training material

header.txt	File to be included in master example ?>
k1.php	A calculation in PHP
k2.php	A calculation with variables
k3.php	Getting a variable from a form - OLD style
k3a.php	Getting a form variable - new and more secure style
k4.php	Example of comment types
master.php	PHP page that calls in an include file ?>
result	Master and Header code merged
simsan.php	Simple sanitisation and sticky field example

Pictures

We ran a PHP course for Pepperdine University

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from http://www.training-notes.co.uk.

Topics covered in this module

Expressions and operators.
Variables.
Getting a value from a form.
Alternative ways of getting values from a form.
Comments in PHP.
Including a file.

Complete learning

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