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

30 Chapter 1 PHP Crash Course
This ability to change types transparently on the fly can be extremely useful.
Remember PHP “automagically” knows what data type you put into your variable. It
returns the data with the same data type when you retrieve it from the variable.
Type Casting
You can pretend that a variable or value is of a different type by using a type cast.This
feature works identically to the way it works in C.You simply put the temporary type in
parentheses in front of the variable you want to cast.
For example, you could have declared the two variables from the preceding section
using a cast:
$totalqty = 0;
$totalamount = (float)$totalqty;
The second line means “Take the value stored in $totalqty, interpret it as a float, and
store it in $totalamount.”The $totalamount variable will be of type float.The cast
variable does not change types, so $totalqty remains of type integer.
You can also use the built-in function to test and set type, which you will learn about
later in this chapter.
Variable Variables
PHP provides one other type of variable: the variable variable.Variable variables enable
you to change the name of a variable dynamically.
As you can see, PHP allows a lot of freedom in this area. All languages enable you to
change the value of a variable, but not many allow you to change the variable’s type, and
even fewer allow you to change the variable’s name.
A variable variable works by using the value of one variable as the name of another.
For example, you could set
$varname = ‘tireqty’;
You can then use $$varname in place of $tireqty. For example, you can set the value of
$tireqty as follows:
$$varname = 5;
This is exactly equivalent to
$tireqty = 5;
This approach might seem somewhat obscure, but we’ll revisit its use later. Instead of
having to list and use each form variable separately, you can use a loop and variable to
process them all automatically.You can find an example illustrating this in the section on
for loops later in this chapter.