📘 Lesson P5 – Conditional Statements (Decision Making)

🎯 Learning Objectives

After completing this lesson, students will be able to:

✅ Understand decision-making in programming

✅ Use if statements

✅ Use if-else statements

✅ Use else if statements

✅ Create multiple decision conditions

✅ Build smart automation logic

✅ Use conditions in real Arduino projects

1. Introduction

Until now, Arduino programs have simply executed instructions one after another.

But real-world systems need to make decisions.

For example:

Smart Fan

If temperature is high

↓

Turn ON fan

Otherwise

↓

Keep fan OFF

Automatic Street Light

If it is dark

↓

Turn ON light

Otherwise

↓

Turn OFF light

Obstacle Avoiding Robot

If obstacle detected

↓

Stop

Otherwise

↓

Move Forward

To make such decisions, we use:

Conditional Statements

2. What is a Conditional Statement?

A conditional statement allows Arduino to execute different instructions based on a condition.

Think of it as asking a question.

Example:

Is temperature greater than 40°C?

If YES:

Turn ON fan

If NO:

Do nothing

3. Real-Life Example

Imagine traffic lights.

Condition:

Is the signal RED?

YES

↓

Stop Vehicle

NO

↓

Move Forward

Traffic systems continuously make decisions.

Arduino works in a similar way.

4. The if Statement

The simplest decision-making statement.

Syntax

if(condition)
{
// Code
}

How It Works

Arduino checks the condition.

If condition is TRUE:

Execute code inside braces.

If condition is FALSE:

Skip the code.

Example

int temperature = 45;

if(temperature > 40)
{
   Serial.println("Fan ON");
}

Output:

Fan ON

Because:

45 > 40

is TRUE.

Example with FALSE Condition

int temperature = 30;

if(temperature > 40)
{
   Serial.println("Fan ON");
}

Output:

Nothing

Because:

30 > 40

is FALSE.

5. Flowchart of if Statement

Start
↓
Check Condition
↓
TRUE? ---- YES ----> Execute Code
↓
NO
↓
Skip Code
↓
Continue Program

6. The if-else Statement

Sometimes we want two possible actions.

Example:

If it is raining

↓

Carry umbrella

Otherwise

↓

Do not carry umbrella

For this we use:

if-else

Syntax

if(condition)
{
   // True Code
}
else
{
   // False Code
}

Example

int temperature = 45;

if(temperature > 40)
{
Serial.println("Fan ON");
}
else
{
Serial.println("Fan OFF");
}

Output:

Fan ON

Example

int temperature = 25;

if(temperature > 40)
{
   Serial.println("Fan ON");
}
else
{
   Serial.println("Fan OFF");
}

Output:

Fan OFF

7. The else if Statement

Sometimes we have multiple conditions.

Example:

Temperature:

• Above 40 → High
• Above 30 → Medium
• Below 30 → Low

This requires:

else if

Syntax

if(condition1)
{
}
else if(condition2)
{
}
else
{
}

Example

int temperature = 35;

if(temperature > 40)
{
Serial.println("High");
}
else if(temperature > 30)
{
Serial.println("Medium");
}
else
{
Serial.println("Low");
}

Output:

Medium

How Arduino Checks Conditions

Step 1:

Check first condition

↓

If TRUE

↓

Execute and stop checking

If FALSE

↓

Check next condition

↓

Continue until a match is found

8. Nested if Statements

An if statement can exist inside another if statement.

Example:

if(cardDetected)
{
if(passwordCorrect)
{
Serial.println("Access Granted");
}
}

Used in:

• Security Systems
• Smart Locks
• Login Systems

9. Using Logical Operators with Conditions

Conditions become powerful when combined with:

AND (&&)

OR (||)

NOT (!)

Example: AND Operator

if(age > 18 && age < 60)
{
   Serial.println("Eligible");
}

Both conditions must be TRUE.

Example: OR Operator

if(score > 90 || attendance > 95)
{
   Serial.println("Reward");
}

Only one condition needs to be TRUE.

Example: NOT Operator

if(!buttonPressed)
{
   Serial.println("Button Not Pressed");
}

Reverses the condition.

10. Real Arduino Project Examples

Automatic Street Light

if(lightValue < 300)
{
   digitalWrite(LED,HIGH);
}
else
{
   digitalWrite(LED,LOW);
}

When dark:

LED turns ON.

Water Tank Monitoring

if(level > 90)
{
   pumpOFF();
}

Tank full.

Gas Leakage Detection

if(gasValue > 500)
{
   buzzerON();
}

Gas detected.

Obstacle Avoiding Robot

if(distance < 10)
{
   stopRobot();
}
else
{
   moveForward();
}

11. Multiple Conditions Example

Student Grade System

int marks = 75;

if(marks >= 90)
{
Serial.println("A");
}
else if(marks >= 80)
{
Serial.println("B");
}
else if(marks >= 70)
{
Serial.println("C");
}
else
{
Serial.println("Fail");
}

Output:

C

12. Common Beginner Mistakes

Mistake 1

Using:

=

instead of:

==

Wrong:

if(temp = 30)

Correct:

if(temp == 30)

Mistake 2

Missing braces.

Wrong:

if(temp > 30)

Serial.println("Hot");

Use braces for clarity.

Mistake 3

Incorrect condition order.

Example:

if(marks > 50)

before

if(marks > 90)

can create logic errors.

Mistake 4

Using too many nested if statements.

Makes code difficult to read.

13. Best Practices

✅ Use meaningful conditions

✅ Keep logic simple

✅ Use indentation properly

✅ Use comments when necessary

✅ Test all conditions

14. Why Conditional Statements are Important

Almost every Arduino project uses decision making.

Examples:

• Smart Door Lock
• Weather Station
• Water Level Controller
• Fire Alarm
• Line Follower Robot
• Obstacle Avoiding Robot
• Home Automation

Without conditional statements, automation would not be possible.

📊 Summary

In this lesson, we learned:

✅ if Statement

✅ if-else Statement

✅ else if Statement

✅ Nested if Statements

✅ Logical Operators with Conditions

✅ Real-world decision-making systems

Conditional statements allow Arduino to make intelligent decisions based on sensor values, user inputs, and program logic.

📖 Key Terms

Condition

An expression that evaluates to TRUE or FALSE.

if

Executes code when condition is TRUE.

else

Executes code when condition is FALSE.

else if

Checks additional conditions.

Nested if

An if statement inside another if statement.

Decision Making

Choosing actions based on conditions.

🎯 Quiz

1. Which statement is used for decision making?

A. loop()

B. if ✅

C. setup()

D. pinMode()

2. What happens if an if condition is FALSE?

A. Program Stops

B. Error Occurs

C. Code Inside if is Skipped ✅

D. Arduino Restarts

3. Which statement handles multiple conditions?

A. while

B. else if ✅

C. setup

D. Serial

4. Which operator means AND?

A. ||

B. !

C. && ✅

D. ==

5. Conditional statements are mainly used for:

A. Decision Making ✅

B. Memory Storage

C. Power Supply

D. Uploading Code

🏠 Assignment

Task 1

Write a program that checks whether a number is positive or negative.

Task 2

Create a temperature monitoring logic that turns ON a fan above 35°C.

Task 3

Create a grade calculator using if-else if.

Task 4

Write three examples using AND (&&) and OR (||) operators.

Task 5

Design the logic for an automatic street light using conditional statements.