Scholar Repository
Home>Manual>Integers

## Integers

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

See also:

### Syntax

Integers can be specified in decimal (base 10), hexadecimal (base 16), or octal (base 8) notation, optionally preceded by a sign (- or +).

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

Example #1 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 structure for integer literals is:

```decimal     : [1-9][0-9]*
| 0

hexadecimal : 0[xX][0-9a-fA-F]+

octal       : 0[0-7]+

integer     : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
```

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. PHP does not support unsigned integers. Integer size can be determined using the constant PHP_INT_SIZE, and maximum value using the constant PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5.

Warning

If an invalid digit is given in an octal integer (i.e. 8 or 9), the rest of the number is ignored.

Example #2 Octal weirdness

```<?php var_dump(01090); // 010 octal = 8 decimal?>```

### 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 #3 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 #4 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 casted to an integer to round it downwards, or the round() function provides finer control over rounding.

```<?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.

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), 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!

Warning

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

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

See also the warning about float precision.

#### 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.

Home>Manual>Integers