Lesson P9 – Strings and Text Handling in Arduino

🎯 Learning Objectives

After completing this lesson, students will be able to:

✅ Understand what Strings are

✅ Understand the difference between char and String

✅ Create and use String variables

✅ Display text using Serial Monitor

✅ Combine Strings

✅ Find String length

✅ Convert text to numbers

✅ Use Strings in Arduino projects

1. Introduction

Until now we have worked with:

• Numbers
• Variables
• Arrays
• Operators

But many Arduino projects also need to handle text.

Examples:

• Displaying messages on LCD
• Sending Bluetooth commands
• Showing sensor status
• Displaying names
• IoT notifications

For these tasks we use:

Strings

2. What is a String?

A String is a collection of characters stored together as text.

Example:

HELLO

contains:

H
E
L
L
O

Multiple characters combined form a String.

Real-Life Example

Examples of Strings:

Arduino
Shiv
Temperature High
Motor ON
Welcome

All of these are Strings.

3. Why Are Strings Important?

Many projects communicate using text.

Examples:

Bluetooth Robot

Command:

FORWARD

LCD Display

Message:

WELCOME

IoT System

Notification:

Temperature High

Without Strings, handling text would be difficult.

4. String Data Type

Arduino provides:

String

for storing text.

Example:

String name = "Shiv";

Here:

name

contains:

Shiv

5. Displaying a String

Example:

String name = "Shiv";

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

   Serial.println(name);
}

void loop()
{

}

Output:

Shiv

6. Creating Multiple Strings

Example:

String city = "Ranchi";

String country = "India";

Output:

Serial.println(city);

Serial.println(country);

Result:

Ranchi
India

7. String vs Character

Students often confuse:

char

and

char

Character

Stores only one character.

Example:

char grade = 'A';

Stores:

A

only.

String

Stores multiple characters.

Example:

String name = "Shiv";

Stores:

Shiv

Comparison

Important Rule

Character uses:

'A'

Single Quotes

String uses:

"Arduino"

Double Quotes

8. Combining Strings

Combining text is called:

Concatenation

Example:

String firstName = "Shiv";

String lastName = "Sahu";

Combine:

String fullName = firstName + " " + lastName;

Output:

String fullName = firstName + " " + lastName;

Practical Example

String city = "Ranchi";

String message = "Welcome to " + city;

Output:

Welcome to Ranchi

9. Finding String Length

Arduino provides:

.length()

Example:

String name = "Arduino";

Serial.println(name.length());

Output:

7

Because:

A r d u i n o

contains 7 characters.

Applications

Useful for:

• Password checking
• Input validation
• Communication systems

10. Accessing Individual Characters

Example:

String name = "Arduino";

Characters:

A r d u i n o
0 1 2 3 4 5 6

Access:

Serial.println(name[0]);

Output:

A

Serial.println(name[3]);

Output:

u

11. Converting Text to Uppercase

Example:

String name = "arduino";

name.toUpperCase();

Serial.println(name);

Output:

ARDUINO

12. Converting Text to Lowercase

Example:

String name = "ARDUINO";

name.toLowerCase();

Serial.println(name);

Output:

arduino

13. Comparing Strings

Example:

String password = "1234";

Check:

if(password == "1234")
{
Serial.println("Access Granted");
}

Output:

Access Granted

Application

Used in:

• Password Systems
• Smart Locks
• Login Systems

14. Converting String to Integer

Sometimes data arrives as text.

Example:

"25"

But we need:

25

as a number.

Use:

.toInt()

Example:

Now:

number = 25

Practical Example

Bluetooth receives:

"100"

Convert to:

100

for motor speed.

15. Reading User Input from Serial Monitor

Example:

String name;

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

void loop()
{
if(Serial.available())
{
name = Serial.readString();

Serial.println(name);
}
}

Whatever user types is displayed back.

Applications

• Bluetooth Commands
• User Input
• Serial Communication

16. Real Arduino Project Examples

Smart Door Lock

String password = "1234";

Compare entered password.

Bluetooth Robot

Commands:

FORWARD
BACKWARD
LEFT
RIGHT
STOP

Stored as Strings.

LCD Welcome Message

String msg = "Welcome";

Display on LCD.

IoT Notifications

String alert = "Gas Leakage Detected";

Send to mobile app.

17. Common Beginner Mistakes

Mistake 1

Using single quotes for Strings.

Wrong:

String name = 'Shiv';

Correct:

String name = "Shiv";

Mistake 2

Using double quotes for char.

Wrong:

char grade = "A";

Correct:

char grade = 'A';

Mistake 3

Ignoring case sensitivity.

Example:

"HELLO"

and

"hello"

are different.

Mistake 4

Creating very large Strings.

Can waste memory on Arduino Uno.

18. Best Practices

✅ Use meaningful names

userName

instead of:

x

✅ Keep Strings reasonably small

✅ Use comments

✅ Validate user input

✅ Test communication systems carefully

📊 Summary

In this lesson, we learned:

✅ What Strings are

✅ String declaration

✅ Displaying text

✅ String concatenation

✅ String length

✅ Character access

✅ String comparison

✅ Text-to-number conversion

Strings allow Arduino to handle text data, making them essential for communication, displays, user interfaces, Bluetooth systems, and IoT projects.

📖 Key Terms

String

A collection of characters forming text.

Character

A single letter, number, or symbol.

Concatenation

Combining multiple Strings.

Length

Number of characters in a String.

toUpperCase()

Converts text to uppercase.

toLowerCase()

Converts text to lowercase.

toInt()

Converts text into an integer.

🎯 Quiz

1. What is a String?

A. Number

B. Collection of characters ✅

C. Sensor

D. Function

2. Which quotation marks are used for Strings?

A. Single Quotes

B. Double Quotes ✅

C. Curly Braces

D. Parentheses

3. Which function returns String length?

A. size()

B. count()

C. length() ✅

D. strlen()

4. What does .toInt() do?

A. Converts number to text

B. Converts text to integer ✅

C. Converts to uppercase

D. Compares Strings

5. Which is a valid String?

A. 'Arduino'

B. "Arduino" ✅

C. Arduino

D. {Arduino}

🏠 Assignment

Task 1

Create a String variable containing your name and display it in Serial Monitor.

Task 2

Create two Strings and combine them into one message.

Task 3

Display the length of a String.

Task 4

Create a simple password checking program using Strings.

Task 5

Research how Bluetooth-controlled robots use Strings for receiving commands such as FORWARD, LEFT, RIGHT, and STOP.