📘 Lesson P6 – Loops in Arduino Programming

🎯 Learning Objectives

After completing this lesson, students will be able to:

✅ Understand what loops are

✅ Understand why loops are needed

✅ Use the for loop

✅ Use the while loop

✅ Use the do-while loop

✅ Understand loop control and repetition

✅ Create repetitive tasks efficiently

✅ Use loops in real Arduino projects

1. Introduction

Imagine you want an LED to blink:

• Turn ON
• Turn OFF

100 times

Would you write:

digitalWrite(13,HIGH);
digitalWrite(13,LOW);

digitalWrite(13,HIGH);
digitalWrite(13,LOW);

digitalWrite(13,HIGH);
digitalWrite(13,LOW);

100 times?

❌ No.

That would make the program unnecessarily long and difficult to manage.

Instead, we use:

Loops

Loops allow Arduino to repeat instructions automatically.

2. What is a Loop?

A loop is a programming structure that repeats a block of code multiple times.

Think of a loop as:

“Do the same task again and again until a condition changes.”

Real-Life Example

Imagine a security guard checking a gate.

He does not check once and go home.

Instead:

Check Gate

↓

Wait

↓

Check Again

↓

Wait

↓

Check Again

↓

Repeat

This repetitive action is similar to a loop.

3. Why Do We Need Loops?

Loops help us:

✅ Reduce code length

✅ Save memory

✅ Improve readability

✅ Automate repetitive tasks

✅ Create efficient programs

Without loops, programming would become very difficult.

4. Types of Loops in Arduino

Arduino supports:

for Loop

while Loop

do-while Loop

These are the most commonly used loops.

5. The for Loop

The for loop is used when we know how many times we want to repeat something.

Syntax

for(initialization; condition; update)
{
// Code
}

Understanding Each Part

Initialization

Runs once at the beginning.

Example:

int i = 0;

Condition

Checked before each repetition.

Example:

i < 5

Update

Runs after each repetition.

Example:

i++

Example 1

for(int i=1; i<=5; i++)
{
   Serial.println(i);
}

Output:

1
2
3
4
5

How It Works

Step 1

i = 1

Print 1

Step 2

i = 2

Print 2

Step 3

i = 3

Print 3

Continue until:

i = 5

After that:

Condition becomes false.

Loop stops.

6. LED Blink Using for Loop

for(int i=0; i<10; i++)
{
   digitalWrite(13,HIGH);
   delay(500);

   digitalWrite(13,LOW);
   delay(500);
}

Result:

LED blinks 10 times.

7. What is a Counter Variable?

In most loops we use:

i

This variable is called a:

Counter Variable

Its job is to count repetitions.

Example

for(int count=1; count<=10; count++)

More meaningful than simply using i.

8. The while Loop

Used when we do not know exactly how many times repetition will occur.

The loop continues while a condition remains true.

Syntax

while(condition)
{
   // Code
}

Example

int count = 1;

while(count <= 5)
{
   Serial.println(count);

   count++;
}

Output:

1
2
3
4
5

How while Works

Arduino checks:

count <= 5

If TRUE:

Run code.

If FALSE:

Stop loop.

Real-Life Example

Imagine filling a water tank.

Continue pumping water

WHILE

Tank is not full.

When tank becomes full:

Stop.

9. Infinite Loop Problem

A common beginner mistake:

while(true)
{
   Serial.println("Hello");
}

This never stops.

Called:

Infinite Loop

Why is it Dangerous?

Program becomes stuck.

Arduino cannot execute other instructions.

Always ensure the loop condition can eventually become false.

Wrong Example

int count = 1;

while(count <= 5)
{
   Serial.println(count);
}

Problem:

count never increases.

Condition remains true forever.

Correct Version

count++;

must be included.

10. The do-while Loop

Similar to while loop.

Difference:

Code executes at least one time.

Syntax

do
{
   // Code
}
while(condition);

Example

int count = 1;

do
{
   Serial.println(count);

   count++;
}
while(count <= 5);

Output:

1
2
3
4
5

Difference Between while and do-while

while

Checks condition first.

May execute zero times.

do-while

Executes once first.

Then checks condition.

At least one execution is guaranteed.

Example

int count = 10;

while(count < 5)
{
   Serial.println("Hello");
}

Output:

Nothing

do-while Version

int count = 10;

do
{
   Serial.println("Hello");
}
while(count < 5);

Output:

Hello

Runs once before checking.

11. Nested Loops

A loop inside another loop.

Example:

for(int i=1;i<=3;i++)
{
   for(int j=1;j<=2;j++)
   {
      Serial.println("Arduino");
   }
}

Output:

Arduino
Arduino
Arduino
Arduino
Arduino
Arduino

Applications of Nested Loops

• LED Matrix Displays
• Pattern Generation
• Advanced Robotics
• Display Systems

12. Real Arduino Project Examples

LED Blink

for(int i=0;i<10;i++)

Blink 10 times.

Automatic Water Dispenser

while(handDetected)

Keep pump running.

Robot Movement

while(distance > 10)

Move forward.

Traffic Signal

for(int i=10;i>0;i--)

Countdown timer.

13. Common Beginner Mistakes

Mistake 1

Missing update statement.

while(count < 10)
{
}

Creates infinite loop.

Mistake 2

Wrong condition.

for(int i=0;i>10;i++)

Loop never runs.

Mistake 3

Using semicolon incorrectly.

Wrong:

for(int i=0;i<5;i++);
{
   Serial.println(i);
}

Mistake 4

Forgetting braces.

Can create unexpected results.

14. Best Practices

✅ Use meaningful variable names

✅ Keep loops simple

✅ Avoid infinite loops

✅ Use comments for complex loops

✅ Test loop conditions carefully

15. Choosing the Right Loop

📊 Summary

In this lesson, we learned:

✅ What loops are

✅ Why loops are needed

✅ for loop

✅ while loop

✅ do-while loop

✅ Infinite loops

✅ Nested loops

Loops allow Arduino to perform repetitive tasks efficiently and are essential for automation, robotics, and embedded systems programming.

📖 Key Terms

Loop

A structure that repeats code.

for Loop

Used when repetitions are known.

while Loop

Runs while condition remains true.

do-while Loop

Executes at least once.

Counter Variable

Variable used to count repetitions.

Infinite Loop

A loop that never ends.

Nested Loop

A loop inside another loop.

🎯 Quiz

1. Which loop is best when the number of repetitions is known?

A. while

B. do-while

C. for ✅

D. if

2. Which loop guarantees at least one execution?

A. for

B. while

C. do-while ✅

D. loop()

3. What is an infinite loop?

A. A loop that executes once

B. A loop that never stops ✅

C. A loop with an error

D. A loop inside another loop

4. Which statement updates the counter?

A. if

B. Serial

C. i++ ✅

D. setup

5. A loop inside another loop is called:

A. Conditional Loop

B. Infinite Loop

C. Nested Loop ✅

D. Logic Loop

🏠 Assignment

Task 1

Write a for loop that displays numbers from 1 to 20 in Serial Monitor.

Task 2

Write a for loop that displays even numbers from 2 to 20.

Task 3

Create a program that blinks an LED 15 times using a for loop.

Task 4

Write a while loop that counts down from 10 to 1.

Task 5

Explain the difference between for, while, and do-while loops with examples.