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

156 Chapter 5 Reusing Code and Writing Functions
Here, the function returns the larger of the two values passed in. It returns an obviously
different value in the case of an error. If one of the numbers is missing, it returns
false. (The only caveat with this approach is that programmers calling the function must
test the return type with === to make sure that false is not confused with 0.)
For comparison, the built-in function max() returns nothing if both variables are not
set and, if only one was set, returns that one.
The code
$a = 1; $b = 2.5; $c = 1.9;
echo larger($a, $b).’’;
echo larger($c, $a).’’;
echo larger($d, $a).’’;
produces this output because $d does not exist and false is not visible:
2.5
1.9
Functions that perform some task but do not need to return a value often return true
or false to indicate whether they succeeded or failed.The boolean values true and
false can be represented with integer values 1 and 0, respectively, although they are of
different types.
Implementing Recursion
Recursive functions are supported in PHP. A recursive function is one that calls itself.These
functions are particularly useful for navigating dynamic data structures such as linked lists
and trees.
Few web-based applications, however, require a data structure of this complexity, so
you have minimal use for recursion. It is possible to use recursion instead of iteration in
many cases because both of these processes allow you to do something repetitively.
However, recursive functions are slower and use more memory than iteration, so you
should use iteration wherever possible.
In the interest of completeness, let’s look at the brief example shown in Listing 5.5.
Listing 5.5