/* Each Arduino sketch must contain the following two functions. */

void setup()
{
  /* this code runs once at the beginning of 
  the code execution. */
}

void loop()
{
  /* this code runs repeatedly over and over
  as long as the board is powered. */
}

// this is a single line
  /* this is
a multiline */

pinMode(pin, [INPUT \ OUTPUT \ INPUT_PULLUP]);
/* Sets the mode of the digital I/O pin. It can be set as an input, output, or an input with an internal pull-up resistor.
*/

if(condition)
{
  // if condition is TRUE, do something here
}
else
{
  // otherwise, do this
}
for(initialization; condition; increment)
{
  // do this
}
/* The ‘for’ statement is used to repeat
a block of statements enclosed in curly
braces. An increment counter is usually
used to increment and terminate the loop.
*/

digitalWrite(pin, val);
  /* val = HIGH or LOW write a HIGH or a LOW
  value to a digital pin. */
  int var = digitalRead(pin);
  /* Reads the value from a specified digital
pin, either HIGH or LOW. */

analogWrite(pin, val);
  /* Writes an analog value to a pin.
  val = integer value from 0 to 255 */
  int var = analogRead(pin);
  /* Reads the value from the specified
analog pin. */

tone(pin, freq);
  /* Generates a square wave of the specified
  frequency to a pin. Pin must be one of the
  PWM (~) pins. */
  tone(pin, freq, duration);
  /* Generates a square wave of the specified
  frequency to a pin for a duration in
  milliseconds. Pin must be one of the PWM (~)
  pins. */
  noTone(pin);
// Turns off the tone on the pin.

delay(time_ms);
  /* Pauses the program for the amount of time
  (in milliseconds). */
  delayMicroseconds(time_us);
  /* Pauses the program for the amount of time
  (in microseconds). */
  millis();
  /* Returns the number of milliseconds since
  the board began running the current program.
  max: 4,294,967,295 */
  micros();
  /* Returns the number of microseconds since
  the board began running the current program.
max: 4,294,967,295 */

HIGH \ LOW
INPUT \ OUTPUT
true \ false

#include 
/* this provides access to special
additional functions for things such as
servo motors, SD card, wifi, or bluetooth.
*/