PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

148 Chapter 5 Reusing Code and Writing Functions
have the same name as any built-in function or an existing user-defined function. Note
that although every PHP script knows about all the built-in functions, user-defined
functions exist only in scripts where they are declared.This means that you could
reuse a function name in a different file, but this would lead to confusion and should
be avoided.
The following function names are legal:
name()
name2()
name_three()
_namefour()
These names are illegal:
5name()
name-six()
fopen()
(The last would be legal if it didn’t already exist.)
Note that although $name is not a valid name for a function, a function call like
$name();
may well execute, depending on the value of $name.The reason is that PHP takes the
value stored in $name, looks for a function with that name, and tries to call it for you.
This type of function is referred to as a variable function and may occasionally be useful
to you.
Using Parameters
To do their work, most functions require one or more parameters. A parameter allows
you to pass data into a function. Here is a sample function that requires a parameter; it
takes a one-dimensional array and displays it as a table:
function create_table($data) {
echo "";
reset($data); // Remember this is used to point to the beginning
$value = current($data);
while ($value) {
echo "".$value."\n";
$value = next($data);
}
echo "";
}
If you call the create_table() function as follows
$my_array = array(‘Line one.’,’Line two.’,’Line three.’);
create_table($my_array);
you will see output as shown in Figure 5.4.