setup() and loop() execution model in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the setup() function in Arduino?

The setup() function runs once when the Arduino starts. It is used to initialize settings like pin modes or start serial communication.

beginner

How often does the loop() function run in an Arduino program?

The loop() function runs repeatedly in a cycle after setup() finishes. It keeps running forever until the board is turned off.

beginner

Why is the loop() function important in Arduino programming?

The loop() function lets the Arduino keep checking sensors, updating outputs, or responding to events continuously, like a heartbeat for the program.

intermediate

What happens if you put code inside setup() instead of loop()?

Code inside setup() runs only once at the start. If you want something to happen repeatedly, it must be inside loop(). Otherwise, it runs just one time.

intermediate

Can setup() or loop() be called manually in Arduino code?

No, Arduino automatically calls setup() once at start and then calls loop() repeatedly. You should not call them yourself.

When does the setup() function run in an Arduino program?

A Once at the start

B Repeatedly forever

C Only when a button is pressed

D Never

The setup() function runs once when the Arduino starts to initialize settings.

What is the main role of the loop() function?

A To initialize variables

B To run code repeatedly

C To stop the program

D To reset the Arduino

The loop() function runs repeatedly to keep the program active and responsive.

If you want to blink an LED continuously, where should the blinking code go?

A Outside both functions

B Inside <code>setup()</code>

C Inside <code>loop()</code>

D In a separate file

Code that runs repeatedly, like blinking an LED, should be inside loop().

Can you call setup() manually in your Arduino sketch?

A No, Arduino calls it automatically once

B Yes, anytime

C Only inside <code>loop()</code>

D Only if you use a special command

Arduino calls setup() automatically once at the start; manual calls are not needed or recommended.

What happens after setup() finishes running?

A The program stops

B The Arduino resets

C Nothing happens

D The <code>loop()</code> function starts running repeatedly

After setup() finishes, loop() runs repeatedly to keep the program active.

Explain how the setup() and loop() functions work together in an Arduino program.

Think about what happens when the Arduino turns on and what happens after.

Describe a real-life example where you would put code inside setup() and code inside loop().

Imagine turning on a device and then it doing something over and over.

Practice

1. What is the main purpose of the setup() function in an Arduino program?

easy

A. To stop the Arduino program

B. To run code repeatedly forever

C. To reset the Arduino board

D. To run code once at the start to prepare the Arduino

Solution

1. Step 1: Understand the role of setup()

   The setup() function runs only once when the Arduino starts. It is used to prepare things like pin modes or initial settings.

2. Step 2: Compare with other options

   loop() runs repeatedly, so To run code repeatedly forever is incorrect. Options A and D describe actions not done by setup().

3. Final Answer:

   To run code once at the start to prepare the Arduino -> Option D

4. Quick Check:

   setup() runs once = C [OK]

Hint: Remember: setup() runs once, loop() runs forever [OK]

Common Mistakes:

• Thinking setup() runs repeatedly
• Confusing setup() with loop()
• Believing setup() resets the board

2. Which of the following is the correct way to declare the loop() function in Arduino?

easy

A. int loop() {}

B. void loop() {}

C. void loop(void) {}

D. loop() void {}

Solution

1. Step 1: Recall Arduino function syntax

   Arduino functions like loop() are declared with return type void and empty parentheses: void loop() {}.

2. Step 2: Check each option

   void loop() {} matches correct syntax. int loop() {} wrongly uses int return type. void loop(void) {} is valid C++ but less common in Arduino examples. loop() void {} has incorrect order.

3. Final Answer:

   void loop() {} -> Option B

4. Quick Check:

   Standard Arduino loop syntax = A [OK]

Hint: Use 'void loop()' exactly as Arduino expects [OK]

Common Mistakes:

• Using wrong return type like int
• Swapping order of function name and return type
• Adding parameters inside loop()

3. What will be the output on the Serial Monitor when running this Arduino code?

void setup() {
  Serial.begin(9600);
  Serial.println("Start");
}

void loop() {
  Serial.println("Looping");
  delay(1000);
}

medium

A. Start and Looping printed once each

B. Only Looping printed repeatedly

C. Start printed once, then Looping printed every second

D. No output because Serial.begin() is missing

Solution

1. Step 1: Analyze setup() output

   Serial.begin(9600) starts serial communication. Serial.println("Start") prints "Start" once at the beginning.

2. Step 2: Analyze loop() output

   loop() prints "Looping" every 1000 milliseconds (1 second) repeatedly.

3. Final Answer:

   Start printed once, then Looping printed every second -> Option C

4. Quick Check:

   setup() once, loop() repeats = B [OK]

Hint: setup() prints once, loop() repeats output [OK]

Common Mistakes:

• Thinking loop() runs once
• Missing Serial.begin() call
• Ignoring delay causing fast prints

4. Identify the error in this Arduino code:

void setup() {
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000)
}

medium

A. Missing semicolon after delay(1000) in loop()

B. pinMode should be in loop(), not setup()

C. digitalWrite cannot be used with pin 13

D. delay() cannot be used inside loop()

Solution

1. Step 1: Check syntax line by line

   In loop(), the line delay(1000) is missing a semicolon at the end.

2. Step 2: Verify other parts

   pinMode is correctly placed in setup(). digitalWrite works with pin 13. delay() is allowed in loop().

3. Final Answer:

   Missing semicolon after delay(1000) in loop() -> Option A

4. Quick Check:

   Syntax error = missing semicolon [OK]

Hint: Check every line ends with a semicolon [OK]

Common Mistakes:

• Placing pinMode in loop() unnecessarily
• Assuming digitalWrite can't use pin 13
• Thinking delay() is disallowed in loop()

5. You want to blink an LED connected to pin 9 exactly 5 times when the Arduino starts, then stop blinking. Which code correctly uses setup() and loop() to do this?

hard

A. Use a counter in setup() to blink 5 times; leave loop() empty

B. Blink 5 times inside loop() without a counter

C. Blink 5 times inside loop() using a counter, then stop blinking

D. Blink 5 times inside setup(), then keep blinking in loop()

Solution

1. Step 1: Understand blinking 5 times only once

   Since blinking 5 times is a one-time task, it should be done in setup() which runs once.

2. Step 2: Keep loop() empty to stop further blinking

   Leaving loop() empty prevents repeated blinking after the initial 5 times.

3. Final Answer:

   Use a counter in setup() to blink 5 times; leave loop() empty -> Option A

4. Quick Check:

   One-time task in setup() = A [OK]

Hint: One-time actions go in setup(), repeated in loop() [OK]

Common Mistakes:

• Blinking in loop() without stopping
• Not using a counter to limit blinks
• Putting one-time code in loop() causing repeats