This example is for Wiring version 0024+. 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.print(num, DEC);
Serial.print(" ");
}