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PHP Pocket Reference, 2nd Edition by Rasmus Lerdorf

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Data Types

PHP provides four primitive data types: integers, floating point numbers, strings, and booleans. In addition, there are two compound data types: arrays and objects.

Integers

Integers are whole numbers. The range of integers in PHP is equivalent to the range of the long data type in C. On 32-bit platforms, integer values range from -2,147,483,648 to +2,147,483,647. PHP automatically converts larger values to floating point numbers if you happen to overflow the range. An integer can be expressed in decimal (base-10), hexadecimal (base-16), or octal (base-8). For example:

$decimal=16;
$hex=0x10;
$octal=020;

Floating Point Numbers

Floating point numbers represent decimal values. The range of floating point numbers in PHP is equivalent to the range of the double type in C. On most platforms, a double can be between 1.7E-308 to 1.7E+308. A double may be expressed either as a regular number with a decimal point or in scientific notation. For example:

$var=0.017;
$var=17.0E-3

PHP also has two sets of functions that let you manipulate numbers with arbitrary precision. These two sets are known as the BC and the GMP functions. See http://www.php.net/bc and http://www.php.net/gmp for more information.

Strings

A string is a sequence of characters. A string can be delimited by single quotes or double quotes:

'PHP is cool'
"Hello, World!"

Double-quoted strings are subject to variable substitution and escape sequence handling, while single quotes are not. For example:

$a="World"; echo "Hello\t$a\n"; ...

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