

An integer is a number of the set
Z = {..., 2, 1, 0, 1, 2, ...}.
See also:
Arbitrary length integer / GMP,
Floating point numbers, and
Arbitrary precision / BCMath
Integers can be specified in decimal (10based), hexadecimal (16based)
or octal (8based) notation, optionally preceded by a sign ( or +).
If you use the octal notation, you must precede the number with a
0 (zero), to use hexadecimal notation precede
the number with 0x.
Example 111. Integer literals <?php
$a = 1234; // decimal number
$a = 123; // a negative number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
?> 

Formally the possible structure for integer literals is:
The size of an integer is platformdependent, although a
maximum value of about two billion is the usual value
(that's 32 bits signed). PHP does not support unsigned
integers.
Warning 
If an invalid digit is passed to octal integer (i.e. 8 or 9), the rest
of the number is ignored.
Example 112. Octal weirdness <?php
var_dump(01090); // 010 octal = 8 decimal
?> 


If you specify a number beyond the bounds of the integer
type, it will be interpreted as a float instead. Also, if
you perform an operation that results in a number beyond the bounds of
the integer type, a float will be returned
instead.
Warning 
Unfortunately, there was a bug in PHP so that this
does not always work correctly when there are negative numbers
involved. For example: when you do 50000 *
$million, the result will be
429496728. However, when both operands are
positive there is no problem.
This is solved in PHP 4.1.0.

There is no integer division operator in PHP.
1/2 yields the float
0.5. You can cast the value to
an integer to always round it downwards, or you can
use the round() function.
To explicitly convert a value to integer, use either
the (int) or the (integer) cast.
However, in most cases you do not need to use the cast, since a value
will be automatically converted if an operator, function or
control structure requires an integer argument.
You can also convert a value to integer with the function
intval().
See also typejuggling.
FALSE will yield
0 (zero), and TRUE
will yield 1 (one).
When converting from float to integer, the number will
be rounded towards zero.
If the float is beyond the boundaries of integer
(usually +/ 2.15e+9 = 2^31),
the result is undefined, since the float hasn't
got enough precision to give an exact integer result.
No warning, not even a notice will be issued in this
case!
Caution 
Behaviour of converting to integer is undefined for other
types. Currently, the behaviour is the same as if the value
was first converted to boolean. However, do
not rely on this behaviour, as it can
change without notice.



