Random Numbers

Syntax#

random(max) //Returns a (long) pseudo-random number between 0 (inclusive) and max (exclusive)
random(min, max) //Returns a (long) pseudo-random number between min (inclusive) and max (exclusive)
randomSeed(seed) //Initializes de pseudo-random number generator, causing it to start at a specified point in its sequence.

Parameters#

Parameter	Details
min	The minimum possible value (inclusive) to be generated by the `random()` function.
max	The maximum possible value (exclusive) to be generated by the `random()` function.
seed	The seed that will be used to shuffle the `random()` function.
## Remarks#
If `randomSeed()` is called with a fixed value (eg. `randomSeed(5)`), the sequence of random numbers generated by the sketch will repeat each time it is run. In most cases, a random seed is preferred, which can be obtained by reading an unconnected analog pin.
## Generate a random number
The `random()` function can be used to generate pseudo-random numbers:

void setup() {
    Serial.begin(9600);
}

void loop() {
    long randomNumber = random(500);  // Generate a random number between 0 and 499
    Serial.println(randomNumber);

    randomNumber = random(100, 1000); // Generate a random number between 100 and 999
    Serial.println(randomNumber);

    delay(100);
}

Setting a seed

If it is important for a sequence of numbers generated by random() to differ, it is a good idea to specify a seed with randomSeed():

void setup() {
    Serial.begin(9600);
    
    // If analog pin 0 is left unconnected, analogRead(0) will produce a
    // different random number each time the sketch is run.
    randomSeed(analogRead(0));
}

void loop() {
    long randomNumber = random(500); // Generate a random number between 0 and 499
    Serial.println(randomNumber);

    delay(100);
}