PHP 5/MySQL Programming- P22 docx

print verse(3);
print chorus();
print verse(4);
print chorus();
The program is to print the first verse, then the chorus, then the second verse,
then the chorus, and so on. The details of how all these things are to be gener-
ated is left to the individual functions. This is an example of
encapsulation
.
Encapsulation is good, because it allows you to think about problems in multiple
levels. At the highest level, you’re interested in the main ideas (print the verses
and chorus) but you’re not so concerned about the exact details. You use the
same technique when you talk about your day: “I drove to work, had some meet-
ings, went to lunch, and taught a class.” You don’t usually describe each detail of
each task. Each major task can be broken down into its component tasks later. (If
somebody asks, you could really describe the meeting: “I got some coffee,
appeared to be taking notes furiously on my PDA, got a new high score on Solitaire
while appearing to take notes, scribbled on the agenda, and dozed off during a
presentation.”)
Returning a Value: The chorus() Function
Another interesting thing about the code’s main section code is the use of the
print() function. In the last program, I simply said chorus() and the program
printed the verse. In this program, I did it a little differently. The
chorus() func-
tion doesn’t actually print anything to the screen. Instead, it creates the chorus
as a big string and sends that value back to the program, which can do whatever
it wants with it.
This behavior isn’t new to you. Think about the
rand() function. It always returns
a value to the program. The functions in this program work the same way. Take
another look at the

chorus() function to see what I mean:
function chorus(){
$output = <<<HERE
with a knick-knack<br>
paddy-whack<br>
give a dog a bone<br>
this old man came rolling home<br>
<br><br>
HERE;
return $output;
} // end chorus
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I began the function by creating a new variable called $output. You can create
variables inside functions by mentioning them, just like you can in the main part
of the program. However, a variable created inside a function loses its meaning
as soon as the function is finished. This is good, because it means the variables
inside a function belong only to that function. You don’t have to worry about
whether the variable already exists somewhere else in your program. You also
don’t have to worry about all the various things that can go wrong if you mis-
takenly modify an existing variable. I assigned a long string (the actual chorus of
the song) to the
$output variable with the <<<HERE construct.
The last line of the function uses the
return statement to send the value of $out-
put
back to the program. Any function can end with a return statement. What-
ever value follows the keyword
return is passed to the program. This is one way
your functions can communicate to the main program.
Accepting a Parameter in the verse() Function
The most efficient part of the newer This Old Man program is the verse() func-
tion. Rather than having a different function for each verse, I wrote one function
that can work for all the verses. After careful analysis of the song, I noticed that
each verse is remarkably similar to the others. The only thing that differentiates
each verse is what the old man played (which is always the verse number) and
where he played it (which is something rhyming with the verse number). If I can
indicate which verse to play, it should be easy enough to produce the correct verse.

Notice that when the main body calls the
verse() function, it always indicates a
verse number in parentheses. For example, it makes a reference to
verse(1) and
verse(3). These commands both call the verse function, but they send different
values (
1 and 3) to the function. Take another look at the code for the verse()
function to see how the function responds to these inputs:
function verse($stanza){
switch ($stanza){
case 1:
$place = “thumb”;
break;
case 2:
$place = “shoe”;
break;
case 3:
$place = “knee”;
break;
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case 4:
$place = “door”;
break;
default:

$place = “I don’t know where”;
} // end switch
$output = <<<HERE
This old man, he played $stanza<br>
He played knick-knack on my $place<br><br>
HERE;
return $output;
} // end verse
In this function, I indicated $stanza as a parameter in the function definition. A
parameter is simply a variable associated with the function. If you create a function
with a parameter, you are required to supply some sort of value whenever you call
the function. The parameter variable automatically receives the value from the main
body. For example, if the program says
verse(1), the verse function is called and the
$stanza variable contains the value 1. I then used a switch statement to populate the
$place variable based on the value of $stanza. Finally, I created the $output variable
using the
$stanza and $place variables and returned the value of $output.
You can create functions with multiple parameters. Simply declare several
variables inside the parentheses of the function definition, and be sure to call the
function with the appropriate number of arguments. Make sure to separate para-
meters with commas.
Managing Variable Scope
You have learned some ways to have your main program share variable informa-
tion with your functions. In addition to parameter passing, sometimes you want
your functions to have access to variables created in the main program. This is
especially true because all the variables automatically created by PHP (such as
those coming from forms) are generated at the main level. You must tell PHP
TRICK
IN THE REAL WORLD

If you’re an experienced programmer, you probably know other ways to make
this code even more efficient. You return to this program as you learn about
loops and arrays in the coming chapters.
when you want a function to use a variable created at the main level. These program-
level variables are also called
global
variables.
If you’ve programmed in another language, you’re bound to get confused by the way
PHP handles global variables. In most languages, any variable created at the main
level is automatically available to every function. In PHP, you must explicitly
request that a variable be global inside a function. If you don’t do this, a new local
variable with the same name (and no value) is created at the function level.
Looking at the Scope Demo
To illustrate the notion of global variables, take a look at the Scope Demo, shown
in Figure 3.16.
Take a look at the code for the
Scope Demo and see how it works:
<html>
<head>
<title>Scope Demo</title>
</head>
<body>
<h1>Scope Demo</h1>
<h3>Demonstrates variable scope</h3>
TRAP
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FIGURE 3.16
Variable $a keeps
its value inside a
function, but $b
does not.
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<?
$a = “I have a value”;
$b = “I have a value”;
print <<<HERE
outside the function, <br>
\$a is “$a”, and<br>
\$b is “$b”<br><br>
HERE;
myFunction();
function myFunction(){
//make $a global, but not $b
global $a;
print <<<HERE
inside the function, <br>
\$a is “$a”, and<br>
\$b is “$b”<br><br>
HERE;
} // end myFunction
?>
</body>
</html>
I created two variables for this demonstration: $a and $b. I gave them both the
value

I have a value. As a test, I printed out the values for both $a and $b.
Notice the trick I used to make the actual dollar sign show up in the quotation
marks. When PHP sees a dollar sign inside quotation marks, it usually expects to
be working with a variable. Sometimes (as in this case) you really want to print a
dollar sign. You can precede a dollar sign with a backslash to have the sign
appear. So, print $a prints the value of the variable $a, but print \$a prints
the value “$a”.
TRICK