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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.

Conditionals.
Conditions are like questions. They allow a program to decide to take one action if the answer to a question is true or to do another action if the answer to the question is false. The questions asked within a program are always logical or relational statements. For example, if the variable 'i' is equal to zero then turn on a light.

    int RED = 8;   // red LED on digital pin 8
    int BLUE = 9;  // blue LED on digital pin 9

    void setup()
    {
      pinMode(RED, OUTPUT);
      pinMode(BLUE, OUTPUT);
    }

    void loop()
    {
      for (int i = 10; i < 32000; i += 10)
      {
        // If 'i' divides by 37 with no remainder turn ON the blue LED
        // else turn ON the red LED
        if (i % 37 == 0)
        {
          digitalWrite(RED, LOW);
          digitalWrite(BLUE, HIGH);
          delay(200);  // delay to visualize the LED change
        }
        else
        {
          digitalWrite(RED, HIGH);
          digitalWrite(BLUE, LOW);
          delay(200);  // delay to visualize the LED change
        }
      }
    }