.. highlight:: cpp

.. _lang-randomseed:

randomSeed()
============

``randomSeed()`` initializes the `pseudorandom number generator
<http://en.wikipedia.org/wiki/Pseudorandom_number_generator>`_,
causing it to start at an arbitrary point in its random sequence.
This sequence, while very long, and random, is always the same.


Library Documentation
---------------------

.. doxygenfunction:: randomSeed

Discussion
----------

If it is important for a sequence of values generated by
:ref:`random() <lang-random>` to differ, on subsequent executions of a
sketch, use ``randomSeed()`` to initialize the random number generator
with a fairly random input, such as :ref:`analogRead()
<lang-analogread>` on an unconnected pin.

Conversely, it can occasionally be useful to use pseudorandom
sequences that repeat exactly. This can be accomplished by calling
``randomSeed()`` with a fixed number, before starting the random
sequence.

Example
-------

The following sketch initializes the random seed based on an :ref:`ADC
<adc>` reading of pin 0.  If this pin is unconnected, the Sketch
should print different values to the :ref:`serial monitor
<ide-serial-monitor>` each time it is run::

    long randNumber;

    void setup() {
      pinMode(0, INPUT_ANALOG);
      randomSeed(analogRead(0));
    }

    void loop() {
      randNumber = random(300);
      SerialUSB.println(randNumber);

      delay(50);
    }

See Also
--------

-  :ref:`random() <lang-random>`

.. include:: /arduino-cc-attribution.txt
