PHP Variables
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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
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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.
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Types
• 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
text.
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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.
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Assignment
• 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.
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Turning DateDisplay into a program
with a variable.
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Result of DateDisplay as variable.
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Incorporating variables within strings.
print "The date is $dateString.";
• The above code also shows how variables
are used in conjunction with strings in
PHP.
• 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.
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If you don’t want the variable value
substituted in, then use single quotes.
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Result of single quoted version of
DateDisplay.
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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.
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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.
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The bells, bells, bells example. (Cont.)
• The first part of the poem talks about silver
bells, the second about gold bells, and so
on.
• So in this example we will vary the image
and the font color for each of the different
parts.
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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
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Where we left off.
More of the same.
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Silver bells turning
into Golden bells as a
result of our variable
being reassigned.
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Constants
• 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.
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Pi page (code)
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Pi page (in browser)
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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
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Some of these
constants tell
one information
about the PHP
server – in this
case the alpha.
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PHP Variables - La Salle University