Checks whether a float is NAN

# is_nan

(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

is_nan — Checks whether a float is NAN

### Description

is_nan(float `$num`): bool

Returns whether the given `num` is `NAN` (Not A Number).

`NAN` is returned from mathematical operations that are undefined, for example when passing parameters outside of function’s input domain. The square root (sqrt()) is only defined for positive numbers, passing a negative number will result in `NAN`. Other examples of operations returning `NAN` are dividing `INF` by `INF` and any operation involving an existing `NAN` value.

> Note:

> Despite its name of Not A Number, `NAN` is a valid value of type float.

Caution

`NAN` does not compare equal to `NAN`. To check whether a float is `NAN`, is_nan() must be used. Checking `$float === NAN` will not work.

### Parameters

`num`

  The float to check

### Return Values

`true` if `num` is `NAN`, else `false`.

### Examples

Example #1 is_nan() example

`<?php
$nan = sqrt(-1);
var_dump($nan, is_nan($nan));
?>`

The above example will output:

    float(NAN)
    bool(true)

### See Also

- is_finite() - Checks whether a float is finite
- is_infinite() - Checks whether a float is infinite

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