## Integers

An integer is a number of the set ℤ = {..., -2, -1, 0, 1, 2, ...}.

See also:

- Arbitrary length integer / GMP
- Floating point numbers
- Arbitrary precision / BCMath

### Syntax

Integers can be specified in decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation. The negation operator can be used to denote a negative integer.

Binary integer literals are available since PHP 5.4.0.

To use octal notation, precede the number with a 0 (zero). To use hexadecimal notation precede the number with 0x. To use binary notation precede the number with 0b.

As of PHP 7.4.0, integer literals may contain underscores (_) between digits, for better readability of literals. These underscores are removed by PHP's scanner.

Example #1 Integer literals

`<?php
$a = 1234; // decimal number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
$a = 0b11111111; // binary number (equivalent to 255 decimal)
$a = 1_234_567; // decimal number (as of PHP 7.4.0)
?>`

Formally, the structure for integer literals is as of PHP 7.4.0 (previously, underscores have not been allowed):

    decimal     : [1-9][0-9]*(_[0-9]+)*
                | 0

    hexadecimal : 0[xX][0-9a-fA-F]+(_[0-9a-fA-F]+)*

    octal       : 0[0-7]+(_[0-7]+)*

    binary      : 0[bB][01]+(_[01]+)*

    integer     : decimal
                | hexadecimal
                | octal
                | binary

The size of an integer is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). 64-bit platforms usually have a maximum value of about 9E18, except on Windows prior to PHP 7, where it was always 32 bit. PHP does not support unsigned integers. Integer size can be determined using the constant `PHP_INT_SIZE`, maximum value using the constant `PHP_INT_MAX` since PHP 5.0.5, and minimum value using the constant `PHP_INT_MIN` since PHP 7.0.0.

Warning

Prior to PHP 7, if an invalid digit was given in an octal integer (i.e. 8 or 9), the rest of the number was ignored. Since PHP 7, a parse error is emitted.

### Integer overflow

If PHP encounters a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the integer type will return a float instead.

Example #2 Integer overflow on a 32-bit system

`<?php
$large_number = 2147483647;
var_dump($large_number); // int(2147483647)
$large_number = 2147483648;
var_dump($large_number); // float(2147483648)
$million = 1000000;
$large_number = 50000 * $million;
var_dump($large_number); // float(50000000000)
?>`

Example #3 Integer overflow on a 64-bit system

`<?php
$large_number = 9223372036854775807;
var_dump($large_number); // int(9223372036854775807)
$large_number = 9223372036854775808;
var_dump($large_number); // float(9.2233720368548E+18)
$million = 1000000;
$large_number = 50000000000000 * $million;
var_dump($large_number); // float(5.0E+19)
?>`

There is no integer division operator in PHP. 1/2 yields the float 0.5. The value can be cast to an integer to round it towards zero, or the round() function provides finer control over rounding.

> Note: As of PHP 7.0.0, the function intdiv() is available for integer division.

`<?php
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
?>`

### Converting to integer

To explicitly convert a value to integer, use either the (int) or (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an integer argument. A value can also be converted to integer with the intval() function.

If a resource is converted to an integer, then the result will be the unique resource number assigned to the resource by PHP at runtime.

See also Type Juggling.

#### From booleans

`FALSE` will yield 0 (zero), and `TRUE` will yield 1 (one).

#### From floating point numbers

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 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms other than Windows), the result is undefined, since the float doesn't have enough precision to give an exact integer result. No warning, not even a notice will be issued when this happens!

> Note:

> As of PHP 7.0.0, instead of being undefined and platform-dependent, NaN and Infinity will always be zero when cast to integer.

Warning

Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.

`<?php
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>`

See also the warning about float precision.

#### From strings

See String conversion to numbers

#### From NULL

`NULL` is always converted to zero (0).

#### From other types

Caution

The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.