Programming PHP

Integers
Integers are whole numbers, like 1, 12, and 256. The range of acceptable values varies
according to the details of your platform but typically extends from –2,147,483,648 to
+2,147,483,647. Specifically, the range is equivalent to the range of the long data type
of your C compiler. Unfortunately, the C standard doesn’t specify what range that
long type should have, so on some systems you might see a different integer range.
Integer literals can be written in decimal, octal, or hexadecimal. Decimal values are
represented by a sequence of digits, without leading zeros. The sequence may begin
with a plus (+) or minus (–) sign. If there is no sign, positive is assumed. Examples of
decimal integers include the following:
1998
-641
+33
Octal numbers consist of a leading 0 and a sequence of digits from 0 to 7. Like decimal
numbers, octal numbers can be prefixed with a plus or minus. Here are some
example octal values and their equivalent decimal values:
0755 // decimal 493
+010 // decimal 8
Hexadecimal values begin with 0x, followed by a sequence of digits (0–9) or letters
(A–F). The letters can be upper- or lowercase but are usually written in capitals. Like
decimal and octal values, you can include a sign in hexadecimal numbers:
0xFF // decimal 255
0x10 // decimal 16
-0xDAD1 // decimal -56017
If you try to store a too-large integer in a variable, it will automatically be turned into
a floating-point number.
Use the is_int( ) function (or its is_integer( ) alias) to test whether a value is an
integer:
if (is_int($x)) {
// $x is an integer
}
Floating-Point Numbers
Floating-point numbers (often referred to as real numbers) represent numeric values
with decimal digits. Like integers, their limits depend on your machine’s details.
PHP floating-point numbers are equivalent to the range of the double data type of
your C compiler. Usually, this allows numbers between 1.7E–308 and 1.7E+308
with 15 digits of accuracy. If you need more accuracy or a wider range of integer values,
you can use the BC or GMP extensions. See Appendix B for an overview of the
BC and GMP extensions.
24 | Chapter 2: Language Basics
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