Listing 4 4 HeadsTailsExample

/*
  Heads or Tails
  Turns on an LED which represents head or tails. The LED 
  remains on for about 3 seconds and the cycle repeats.
 
   Dr. Purdum, Nov 12, 2014
 */

#define HEADIOPIN     11  // Which I/O pins are we using?
#define TAILIOPIN     10

#define PAUSE         50      // How long to delay?

int headsCounter;       // Heads/tails counters
int tailsCounter;

long loopCounter;
long randomNumber = 0L;  // 'L' tells compiler it's a long data type, 
                         // not an int.

// the setup routine runs once when you press reset:
void setup() {
  Serial.begin(9600);
  headsCounter = 0;
  tailsCounter = 0;
  loopCounter = 0;

  pinMode(HEADIOPIN, OUTPUT);
  pinMode(TAILIOPIN, OUTPUT);
  randomSeed(analogRead(A0)); // This seeds the random number generator
}

void loop() {

  randomNumber = generateRandomNumber();
  digitalWrite(HEADIOPIN, LOW);      // Turn both LED's off
  digitalWrite(TAILIOPIN, LOW);

  delay(PAUSE);          // Let them see both are off for a time slice

  if (randomNumber % 2 == 1) {           // Treat odd numbers as a head
    digitalWrite(HEADIOPIN, HIGH);
    headsCounter++;
  } else {
    digitalWrite(TAILIOPIN, HIGH);       // Even numbers are a tail
    tailsCounter++;
  }
  loopCounter++;
  if (loopCounter % 100 == 0) {  // See how things are every 100 flips
    Serial.print("After ");
    Serial.print(loopCounter);
    Serial.print(" coin flips, heads = ");
    Serial.print(headsCounter);
    Serial.print(" and tails = ");
    Serial.println(tailsCounter);
  }
  delay(PAUSE);                  // Pause for 3 seconds
}

long generateRandomNumber()
{
  return random(0, 1000000);        // Random numbers between 0 and one million
}