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>> PROFESSOR: Let's write a program that
keeps track of how many times a user

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has visited a web page, thereby
demonstrating how you can use PHP's

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feature known as a session.

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Let's get started by first taking a look
at the HTML that I've prepared in

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advance here.

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Notice that I have put in the body of
this page the statement, you have

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visited the site this many times,
whereby this many is going to be the

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result of outputting a variable that's
apparently called dollar sign counter.

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>> Now, up at the top of this file I've
left some space between an open tag

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and a closed tag for some PHP code.

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Let's now start a session by
specifying the following.

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Session_start and calling
that function.

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What that simply does is inform PHP
that I would like to begin using

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Session so that the super global, dollar
sign underscore session, is

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available to me.

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And PHP and the web server will,
therefore, magically take care of how

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that variable is actually implemented
back and forth between client and

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server, somehow using cookies.

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>> But in code, what I next want to do
is something like the following.

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First, let's check if there's already
a variable set in my session.

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If is set dollar sign underscore
session quote unquote counter.

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In other words, I'm going to use the
session super global to store a key,

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also called counter, whose value is
going to be the total number of times

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that the user has visited my site, and
I'll grab that value as needed and put

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it in my local variable, dollar
sign counter, in order to

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display that value.

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>> Next, if that key is indeed set with a
value, I'm going to go ahead and grab

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that value with dollar sign counter gets
dollar sign underscore session

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open bracket quote unquote counter
close bracket semicolon.

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If that variable is not set, let's
simply initialize counter with the

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value zero.

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Meanwhile, no matter what happens up
there, let's update dollar sign

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underscore session quote unquote counter
to be whatever this local

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variable is plus 1.

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>> I claim, now, by way of this branch and
a bit of arithmetic, I am going to

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start counting how many times the
user has visited this page.

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Let's take a look.

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Let's save the file and open
it up in a browser.

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>> Let's visit
http://localhost/counter/php.

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This is the first time I'm here so,
indeed, I visited the site zero times.

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But let's now reload, let's now reload,
let's now reload, and as

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expected, I've now visited this site
not zero, but three times.

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