PHP Variables
What is a variable?
• A variable is something that can be changed – a
thing that can take on any value from a possible
set of values.
– For example, the number of hours someone works in
a given week is a variable.
• In math, a symbol is used in place of the variable
to express a relationship between some quantity
and the variable
– For example, pay is one’s pay rate times the number
of hours worked
– Pay = PayRate * NumberHours
What is a variable? (Cont.)
• So a variable is something that stands in for a
quantity that might vary.
• In programming, a variable can be thought of a
referring to a memory location or set of memory
locations. The value of the variable at any given
time is then the contents of that memory location
• As we said a variable can take on values from a
set of possible values, the set of values is
determined in part by the variable’s type.
• Unlike many other programming
languages, PHP variables do not have to
be “declared.” In such a case, a variable’s
types tends to come from its context.
– Standard types includes numbers (both
integers and so-called floating point
numbers that can have fraction parts.
– Another standard type is a string,which can
used for names of things or just about any
PHP variable rules
• In PHP a variable starts with a dollar sign.
• After that must come a letter or an
underscore (no numbers).
• After that can come letters or numbers.
• There can be no spaces in the name.
• A variable is said to be assigned a value in an
assignment statement. E.g.
$NumberHours = 45;
$WorkerFirstName = “Pete”;
• The assignment statement should not be thought of as
expressing mathematical equality rather it a set of
instructions to evaluate the expression on the right hand
side and give the variable on the left hand side the value
that results. Thus
$Counter = $Counter + 1;
Makes sense as an assignment statement even though
it makes no sense as mathematics.
Turning DateDisplay into a program
with a variable.
Result of DateDisplay as variable.
Incorporating variables within strings.
print "The date is $dateString.";
• The above code also shows how variables
are used in conjunction with strings in
• Within the string (set of characters within
quotes) that will appear literally (“as is”),
the variable does not appear as is, rather
its value is substituted into the string.
If you don’t want the variable value
substituted in, then use single quotes.
Result of single quoted version of
That variable doesn’t vary much.
• Because these are PHP variables, all of
their variation takes place on the server
side (before the PHP preprocessed page
is sent to the client).
• PHP variables will ultimately give us
interaction with the viewer of the page but
always through a process in which
information is sent back to the server.
The bells, bells, bells example.
• Before consider variables determined by
interaction with a user, let us consider one
example in which the variable does vary.
• In Edgar Allen Poe’s poem The Bells, the
word “bells” appears over and over again.
Let’s substitute in an image of bells in
place of the word bells.
– So far substitution (a lot of it) but not variation.
The bells, bells, bells example. (Cont.)
• The first part of the poem talks about silver
bells, the second about gold bells, and so
• So in this example we will vary the image
and the font color for each of the different
Assigning the variables
Writing some HTML
A chunk of the poem, with
the word bells replaced
with the variable $bells.
Note that the quotation
can be spread out over
many lines. (That would
ne a no-no in C.)
Re-assigning the variables
Where we left off.
More of the same.
Silver bells turning
into Golden bells as a
result of our variable
being reassigned.
• If you really want a quantity that is going to
take on a value and never change then
what you want is called a constant.
• Constants do not start with dollar signs.
• By convention, constant names are in all
capital letters.
Pi page (code)
Pi page (in browser)
PHP’s Global Constants
The <pre> tag tells HTML to respect the
white space of the text between the tags.
The function print_r is for printing
arrays – GLOBALS is not one
constant but a set of constants
Some of these
constants tell
one information
about the PHP
server – in this
case the alpha.

PHP Variables - La Salle University