Sketch

The arduino code has two basic "Functions", these functions are a requirement to the sketch to run, other functions can be define and use inside this basic loops, these basic function are:

• Setup function.
• Loop function.

setup() function

The setup() function is called when a sketch starts. Use it to initialize variables, pin modes, start using libraries, etc. The setup() function will only run once, after each powerup or reset of the Arduino board.

void setup(){

}

one of the statement that are going to be in this function, or that are commonly found, is the function to communicate with the serial port, Serial.begin(9600); this is standard and basically is feeding 960 characters per second over the serial

int buttonPin = 3;

void setup() {
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

void loop() {
  // ...
}

loop() function

After creating a setup() function, which initializes and sets the initial values, the loop() function does precisely what its name suggests, and loops consecutively, allowing your program to change and respond. Use it to actively control the Arduino board.

int buttonPin = 3;

// setup initializes serial and the button pin
void setup() {
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}

// loop checks the button pin each time,
// and will send serial if it is pressed
void loop() {
  if (digitalRead(buttonPin) == HIGH) {
    Serial.write('H');
  }
  else {
    Serial.write('L');
  }

  delay(1000);
}