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This example is for Wiring version 1.0 build 0100+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

Modulo.
The modulo operator (%) returns the remainder of a number divided by another. As in this example, it is often used to keep numerical values within a set range.

    int num = 0;

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

    void loop()
    {
      num = (num + 1) % 10;  // num goes from 0 to 9
      Serial.println(num, DEC);
      delay(50);
    }