Comments in Your Sketch

Part of the First Circuits section of Coddy's Arduino journey. Lesson 6 of 22.

A comment is a note for people. The board skips it. Two slashes // turn the rest of the line into a comment:

digitalWrite(8, HIGH);  // red on

For a comment over several lines, start it with /* and end it with */:

/* Blink the red LED.
   It is on pin 8. */

Comments explain what the code is for, so you and others can read it later. They have a second use: put // in front of a line and the board ignores it, without you deleting it. This is called commenting out a line. Remove the // and the line is back.

To switch off an LED this way, comment out every line that uses its pin. A pin that was never made an output, but is still set HIGH, can make an LED glow faintly.

Challenge

Easy

The starter blinks a red LED (pin 8) and a yellow LED (pin 9) together. Make only the red one blink, without deleting any line:

comment out the three lines that use pin 9, with // or /* */
keep every line for pin 8 as it is

Press Run, then Check.

Try it yourself

/* Two LEDs blink together:
   red on pin 8, yellow on pin 9. */

void setup() {
  pinMode(8, OUTPUT);  // red
  pinMode(9, OUTPUT);  // yellow
}

void loop() {
  digitalWrite(8, HIGH);
  digitalWrite(9, HIGH);
  delay(500);
  digitalWrite(8, LOW);
  digitalWrite(9, LOW);
  delay(500);
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in First Circuits

1Hello, Board

Blink an LED Setup and Loop Change the Blink Speed An LED of Your Own Two LEDs Taking TurnsComments in Your Sketch

4Decisions

Decisions with if Choosing with if and else Comparing Values Combining Conditions Read a Button

2Talking to Your Computer

Hello, Serial Monitor Print Versus Println Printing Numbers Your First Variable Counting Up When an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer Division Decimals with float A Blink That Speeds Up

Practice on your own: Arduino playground