setup() and loop() execution model in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Arduino sketch?

Consider the following Arduino code. What will be printed to the Serial Monitor after the board resets and runs this code?

Arduino

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

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

A Start\nLooping\nLooping\nLooping\n... (repeats every second)

B Looping\nLooping\nLooping\n... (repeats every second)

C Start\nStart\nStart\n... (repeats every second)

D No output because Serial.begin() is missing

💡 Hint

Remember that setup() runs once and loop() runs repeatedly.

The setup() function runs once when the Arduino starts, printing "Start". Then loop() runs repeatedly, printing "Looping" every second.

🧠 Conceptual

intermediate

How many times does setup() run in an Arduino program?

In an Arduino sketch, how many times is the setup() function executed during normal operation?

A Twice, once at start and once after loop()

B Repeatedly, every time loop() finishes

C Never, it is optional

D Once, when the board powers on or resets

💡 Hint

Think about what happens when you reset the Arduino.

setup() runs only once at the start after power on or reset. loop() runs repeatedly after that.

🔧 Debug

advanced

Why does this Arduino code print "Start" repeatedly?

This code prints "Start" repeatedly every second instead of just once. What is the cause?

Arduino

void setup() {
  Serial.begin(9600);
}

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

A Because delay(1000) causes setup() to rerun

B Because setup() is called repeatedly by Arduino

C Because the print statement is inside loop(), it runs repeatedly

D Because Serial.begin() restarts the program

💡 Hint

Check where the print statement is placed.

The print statement is inside loop(), which runs repeatedly, so "Start" prints every second.

📝 Syntax

advanced

Which option causes a compilation error in Arduino?

Which of the following Arduino sketches will NOT compile?

A

void setup() { }
void loop() { }

B

void setup() { }
void loop() { return 0; }

C

void setup() { }
void loop() { int x = 5; }

D

void setup() { int a = 1; }
void loop() { }

💡 Hint

Remember the return type of loop() is void.

loop() is declared void and cannot return a value. 'return 0;' causes a compilation error.

🚀 Application

expert

How many times will the LED blink in this Arduino sketch?

Given this Arduino code, how many times will the LED connected to pin 13 blink after the board resets?

Arduino

int count = 0;

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

void loop() {
  if (count < 3) {
    digitalWrite(13, HIGH);
    delay(500);
    digitalWrite(13, LOW);
    delay(500);
    count++;
  }
}

A 3 times

B Infinite times

C 0 times

D 1 time

💡 Hint

Look at how the count variable controls blinking.

The LED blinks while count is less than 3. After 3 blinks, loop() does nothing but runs endlessly.

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