PHP 5/MySQL Programming- P28 pdf

A program begins running, might ask the user some questions, responds to these inputs, and continues interacting with the user until he indicates an interest in leaving the program.. Whe

Building the Place Array

I notice that each place is a string value associated with some number I use the

array()directive to preload the $placearray with appropriate values Zero has no

corresponding place, so I simply left the 0element blank

$place = array(

“”,

“on my thumb”,

“on my shoe”,

“on my knee”,

“on a door”);

Like most places in PHP, carriage returns don’t matter when you’re writing the

source code I put each place on a separate line, just because it looked neater that

way

Writing Out the Lyrics

The song itself is incredibly repetitive Each verse is identical except for the verse

number and place For each verse, the value of the $versevariable is the current

verse number The corresponding place is stored in $place[$verse] A large print

statement in a forloop prints the entire code

//print out song

for ($verse = 1; $verse <= 4; $verse++){

print <<<HERE

This old man, He played $verse

He played knick-knack $place[$verse]

with a knick, knack, paddy-whack

give a dog a bone

This old man came rolling home

HERE;

} // end for loop

The Fancy Old Man program illustrates very nicely the tradeoff associated with

using arrays Creating a program that uses arrays correctly often takes a little more

planning than using control structures alone (as in This Old Man) However, the

extra work up front pays off because the program is easier to modify and extend

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Keeping Persistent Data

Most traditional kinds of programming presume that the user and the program are engaging in a continual dialog A program begins running, might ask the user some questions, responds to these inputs, and continues interacting with the user until he indicates an interest in leaving the program

Programs written on a Web server are different The PHP programs you are writ-ing have an incredibly short life span When the user makes a request to your PHP program through a Web browser, the server runs the PHP interpreter(the pro-gram that converts your PHP code into the underlying machine language your server understands) The result of the program is a Web page that is sent back to the user’s browser Once your program sends a page to the user, the PHP program shuts down because its work is done Web servers do not maintain contact with the browser after sending a page Each request from the user is seen as an entirely new transaction

The Poker Diceprogram at the beginning of this chapter appears to interact with the user indefinitely Actually, the same program is being called repeatedly The program acts differently in different circumstances Somehow it needs to keep track of what state it’s currently in

Counting with Form Fields

You can store information a couple of ways, including files, XML, and databases The second half of this book details these important ideas The easiest approach

to achieving data permanence is to hide the data in the user’s page To illustrate, take a look at Figures 4.9 and 4.10

I N THE R EAL W ORLD

The underlying Web protocol (HTTP) that Web servers use does not keep con-nections open any longer than necessary This behavior is referred to as being a stateless protocol Imagine if your program were kept running as long as any-body anywhere on the Web were looking at it What if a person fired up your program and went to bed? Your Web server would have to maintain a connec-tion to that page all night Also remember that your program might be called by thousands of people all at the same time

It can be very hard on your server to have all these concurrent connections open Having stateless behavior improves your Web server’s performance, but that per-formance comes at a cost Essentially, your programs have complete amnesia every time they run You need a mechanism for determining the current state.

Each time you click the Persistenceprogram’s submitbutton, the counters

incre-ment by one The program behavior appears to contradict the basic nature of

server-side programs because it seems to remember the previous counter value

In fact, if two users were accessing the Persistenceprogram at the same time,

each would count correctly Look at the source code to see how it works:

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FIGURE 4.9

The program has

two counters that

read 1 when the

program is run

the first time.

FIGURE 4.10

Both values are

incremented after

the user clicks the

submit button.

<head>

<title>

persistence demo

</title>

</head>

<body>

<h1>Persistence Demo</h1>

<form>

<?

//increment the counters

$txtBoxCounter++;

$hdnCounter++;

print <<<HERE

<input type = “text”

name = “txtBoxCounter”

value = “$txtBoxCounter”>

<input type = “hidden”

name = “hdnCounter”

value = “$hdnCounter”>

<h3>The hidden value is $hdnCounter</h3>

<input type = “submit”

value = “click to increment counters”>

HERE;

?>

</form>

</body>

</html>

Storing Data in the Text Box

The program has two variables: $txtBoxCounter and $hdnCounter For now, con-centrate on $txtBoxCounter, which is related to the text box When the program

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begins, it grabs the value of $txtBoxCounter(if it exists) and adds one to it When

the program prints the text box, it automatically places the $txtBoxCountervalue

in the text box

Since the form has no action attribute defined, the program automatically calls

itself when the user clicks the submit button This time, $txtBoxCounter has a

value (1) When the program runs again, it increments $txtBoxCounterand stores

the new value (now 2) in the text box Each time the program runs, it stores in

the text box the value it needs on the nextrun

Using a Hidden Field for Persistence

The text box is convenient for this example because you can see it, but using a

text box this way in real programs causes serious problems Text boxes are

editable by the user, which means she could insert any kind of information and

really mess up your day

Hidden form fields are the unsung heroes of server-side programming Look at

$hdnCounterin the source code This hidden field also has a counter, but the user

never sees it However, the value of the $hdnCounter variable is sent to the PHP

program indicated by the form’s actionattribute That program can do anything

with the attribute, including printing it in the HTML code body

Very often when you want to track information between pages, you store the

information in hidden fields on the user’s page

The hidden fields technique shown here works fine for storing small amounts of information, but it is very inefficient and insecure when you are working with more serious forms of data

Writing the Poker Dice Program

It’s time to take another look at the Poker Diceprogram that made its debut at the

beginning of this chapter As usual, this program doesn’t do anything you haven’t

already learned It is a little more complex than the trivial sample programs I show

you in this chapter, but it’s surprisingly compact considering how much it does It

won’t surprise you that arrays and loops are the secret to this program’s success

Setting Up the HTML

As always, a basic HTML page serves as the foundation for the PHP program I add

a simple style sheet to this page to make tan characters on a green background

T R A P

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