When AverageTemperature is first used, PHP marks it internally as a string because it is
assigned the value of a string literal. Setting the type to be double causes the value to be
reevaluated. If you check the output, youwill notice that some information is lost as a
result. The text following the number is dropped off because it has no meaning in the
context of a floating-point number. Likewise, when the script sets the type to be integer,
the fractional part of the number is dropped. Even when we change the type back to
string, the previous information is gone.
In contrast to this, the use of the type conversion commands preserves the value of the
variable because it does the conversion on the fly. The data inside the variable are not
changed.
The settype function is described in full in Chapter 9, "Data Functions," as are the type
conversion functions intval, strval , and doubleval. Casts, identical in operation to
type conversion functions, take the form of preceding an expression with a datatype in
parentheses. Valid casts are (boolean), (integer), (string), (double), (array)
, and (object). Arrays and objects are discussed in Chapters 5 and 6.
Another type of data sometimes discussed in this text is the bitfield. Rather than a data
type exactly, it is a way of viewing an integer. Instead of a single value, it is viewed as a
sequence of ones and zeroes. Bitfields are discussed later in this chapter in relation to
Bitwise Operators...............................................................................................
Variable Creation and Scope
Although you've seen variables in the previous pages, you may wonder what they are
exactly. Part of a computer is called RAM, or random access memory. This is a volatile
medium for storing information. That is, it all disappears when you shut off the machine.
The computer sees this memory as a long string of single characters, or bytes, each
numbered. In PHP, however, you cannot actually get to memory at this level. You must
use a variable. You provide a name, and PHP takes care of matching the name to physical
memory.
Listing 2.2 Experimenting with Scope