PHP Data Types

PHP supports many different data types, but they are generally divided in two categories:
scalar and composite.

A scalar value contains only one value at a time. PHP supports four scalar types:
boolean A value that can only either be true or false

int 
A signed numeric integer value

float 
A signed floating-point value

string 
A collection of binary data

Numeric Values
PHP recognizes two types of numbers, integers and floating-point values. The int
data type is used to represent signed integers (meaning that both positive and negative
numbers can be expressed with it). Numbers can be declared using several
different notations:

Decimal 
10; -11; 1452 Standard decimal notation. Note that no
thousand separator is needed—or, indeed,
allowed.

Octal 
0666, 0100 Octal notation—identified by its leading zero
and used mainly to express UNIX-style access
permissions.

Hexadecimal 
0x123; 0XFF; -0x100 Base-16 notation; note that the
hexadecimal digits and the leading
0x prefix are both case-insensitive.

Floating-point numbers (also called floats and, sometimes, doubles) are numbers
that have a fractional component; like integers, they are also signed. PHP supports
two different notations for expressing them:

Decimal 
0.12; 1234.43; -.123 Traditional decimal notation.

Exponential 
2E7, 1.2e2 Exponential notation—a set of
significant digits (also called the
mantissa), followed by the
case-insensitive letter E and by an
exponent. The resulting number is
expressed multiplied by ten to the
power of the exponent—for
example, 1e2 equals 100.


for example this
very simple statement:
echo (int) ((0.1 + 0.7) * 10);

You would expect that the expression ((0.1 + 0.7) * 10) would evaluate to 8 (and,
in fact, if you print it out without the integer conversion, it does). However, the statement
above outputs 7 instead. This happens because the result of this simple arithmetic
expression is stored internally as 7.999999 instead of 8; when the value is converted
to int, PHP simply truncates away the fractional part, resulting in a rather
significant error (12.5%, to be exact).

The lesson that you need to take home from all this is simple: know the limitations
of your numeric data types, and plan around them. Whenever the precision of your
calculation is a relevant factor to the proper functioning of your application, you
should consider using a the arbitrary precision functions provided by the BCMath
extension (you can search for it in your copy of the PHP manual) instead of PHP’s
built-in data types.

Strings
In the minds of many programmers, strings are equivalent to text. While in some
languages this is, indeed, the case, in many others (including PHP), this would be a
very limiting—and, in some cases, incorrect—description of this data type. Strings
are, in fact, ordered collections of binary data—this could be text, but it could also
be the contents of an image file, a spreadsheet, or even a music recording.
PHP provides a vast array of functionality for dealingwith strings. As such,we have
dedicated a whole chapter to them—entitled, quite imaginatively, Strings.

Booleans
A Boolean datum can only contain two values: true or false. Generally speaking,
Booleans are used as the basis for logical operations, which are discussed later in
this chapter.
When converting data to and from the Boolean type, several special rules apply:

• A number (either integer or floating-point) converted into a Boolean becomes false if the original value is zero, and true otherwise.
• A string is converted to false only if it is empty or if it contains the single character 0. If it contains any other data—even multiple zeros—it is converted to true.
• When converted to a number or a string, a Boolean becomes 1 if it is true, and 0 otherwise.

Compound Data Types
In addition to the scalar data type that we have just examined, PHP supports two
compound data types—so called because they are essentially containers of other
data:

• Arrays are containers of ordered data elements; an array can be used to store and retrieve any other data type, including numbers, Boolean values, strings, objects and even other arrays. They are discussed in the Arrays chapter
• Objects are containers of both data and code. They form the basis of Objectoriented Programming, and are also discussed in a separate chapter calledObject Oriented Programming in PHP.

Other Data Types
In addition to the data types that we have seen so far, PHP defines a few additional
types that are used in special situations:

• • NULL indicates that a variable has no value. A variable is considered to be NULL if it has been assigned the special value NULL, or if it has not yet been assigned a value at all—although in the latter case PHP may output a warning if you attempt to use the variable in an expression.
• The resource data type is used to indicate external resources that are not used natively by PHP, but that have meaning in the context of a special operation—such as, for example, handling files or manipulating images.

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