How to Convert Integer to String on Arduino?

In the world of Arduino programming, a common question that often arises is how to convert an integer to a string. This procedure is essential in many scenarios, such as when you need to print numerical values or when you want to concatenate numbers with text.

This article provides a comprehensive guide on various methods to perform this conversion effectively. We will delve into multiple functions like dtostrf(), sprintf(), and the String() class, offering a step-by-step approach to each. Whether you’re a beginner or a seasoned Arduino programmer, this guide aims to make the process of converting integers to strings straightforward and efficient.

What Is Integer on Arduino?

When working with Arduino, understanding data types is essential, as it forms the foundation of your programming endeavors. Among the most fundamental data types is the integer, often abbreviated as int.

Before delving into integers specifically, let’s take a moment to discuss data types in the context of programming. In the world of computing, data types define the kind of data a variable can hold and the operations that can be performed on it. Data types ensure that the right operations are performed on the right kind of data, preventing errors and ensuring that your code behaves as expected.

Declaring Integer Variables:

• In Arduino, declaring an integer variable is straightforward. You simply use the int keyword followed by a variable name, like this: int myInteger;
• This line of code declares an integer variable named myInteger. You can also initialize it with a value at the time of declaration: int myInteger = 42;
• Now, myInteger is initialized with the value 42. You can change the value of an integer variable at any time during your program’s execution: myInteger = 20;

Using Integers in Arduino

Integers are commonly used for a variety of purposes in Arduino programming.

Here are some examples of their applications:

Counting and Indexing

Integers are often used to count events or as indices for arrays. For instance, if you want to control an array of LEDs, you might use an integer variable to keep track of which LED is currently active.

int ledPin = 2;

int numberOfLEDs = 5;

void setup() {

// Initialize the LED pin as an output

pinMode(ledPin, OUTPUT);

}

void loop() {

for (int i = 0; i < numberOfLEDs; i++) {

digitalWrite(ledPin, HIGH);

delay(1000);

digitalWrite(ledPin, LOW);

delay(1000);

}

}

In this example, the int i variable is used as a counter to iterate through the LEDs.

Storing Sensor Readings

When working with sensors, you often obtain analog or digital readings that need to be stored. Integer variables can hold these readings.

int sensorValue;

void setup() {

// Initialize the serial communication

Serial.begin(9600);

}

void loop() {

// Read a sensor value

sensorValue = analogRead(A0);

// Print the sensor value to the serial monitor

Serial.println(sensorValue);

// Wait for a short time

delay(1000);

}

In this code, the sensorValue variable stores the reading from an analog sensor [2].

Mathematical Operations

Integers are also used in mathematical operations. You can perform addition, subtraction, multiplication, and division on integer variables.

int x = 5;

int y = 3;

int result;

void setup() {

// Initialize the serial communication

Serial.begin(9600);

}

void loop() {

// Perform addition

result = x + y;

Serial.print(“Addition: “);

Serial.println(result);

// Perform subtraction

result = x – y;

Serial.print(“Subtraction: “);

Serial.println(result);

// Perform multiplication

result = x * y;

Serial.print(“Multiplication: “);

Serial.println(result);

// Perform division

result = x / y;

Serial.print(“Division: “);

Serial.println(result);

delay(1000);

}

In this example, we perform various mathematical operations using integer variables.

What Is String on Arduino?

Now that we have a good understanding of integers in Arduino, let’s shift our focus to another essential data type: strings. Strings are a data type used to store and manipulate text and characters. In the context of Arduino programming, strings can be incredibly useful for handling textual data, such as messages, sensor data labels, and communication with other devices.

Understanding Strings

A string is essentially an array of characters. Each character in a string is stored in a specific order, and you can access and manipulate individual characters or the entire string. Strings are versatile and can hold letters, numbers, symbols, and even whitespace.

Declaring String Variables

To declare a string variable in Arduino, you use the String keyword followed by a variable name, like this:

String myString;

You can also initialize a string with a value at the time of declaration:

String greeting = “Hello, Arduino!”;

This line of code initializes a string variable named greeting with the text “Hello, Arduino!”.

Using Strings in Arduino

Strings are incredibly handy in Arduino programming, particularly when dealing with text-based data.

Here are some common use cases for strings:

1. Displaying Messages

You can use strings to display messages on an LCD screen or through serial communication.

String message = “Temperature: “;

int temperature = 25;

void setup() {

// Initialize the serial communication

Serial.begin(9600);

}

void loop() {

// Concatenate the message and temperature value

String fullMessage = message + temperature;

// Display the message

Serial.println(fullMessage);

delay(1000);

}

In this example, the message and temperature variables are combined into a single string for display [3].

2. Parsing Data

When you receive data as text, you can use string functions to extract and manipulate specific parts of the data. For instance, if you receive a sensor reading as a string, you can extract the numeric value.

String data = “Sensor: 42.5”;

void setup() {

// Initialize the serial communication

Serial.begin(9600);

}

void loop() {

// Find the position of the colon

int colonPosition = data.indexOf(‘:’);

// Extract the numeric part of the string

String numericPart = data.substring(colonPosition + 2);

// Convert the numeric part to a float

float sensorValue = numericPart.toFloat();

// Display the sensor value

Serial.println(sensorValue);

delay(1000);

}

In this code, we use string functions like indexOf() and substring() to parse the data.

3. Sending Data

When communicating with other devices or microcontrollers, you often need to send data as strings. For example, when sending data to a web server, you might need to convert sensor readings to strings for transmission.

float temperature = 25.5;

String dataToSend;

void setup() {

// Initialize the serial communication

Serial.begin(9600);

}

void loop() {

// Convert the temperature to a string

dataToSend = String(temperature);

// Send the data to a server or another device

sendDataToServer(dataToSend);

delay(1000);

}

void sendDataToServer(String data) {

// Code to send data to a server goes here

}

In this example, the temperature variable is converted to a string before sending it to a server.

Why Should You Convert Integer to String?

Now that we have a solid understanding of both integers and strings in the Arduino environment, let’s explore why it’s often necessary to convert integers to strings. This conversion process is essential in various scenarios where you need to work with both numerical data and text data within your Arduino projects.

Displaying Numeric Data

One of the primary reasons to convert an integer to a string is for displaying numeric data. Many displays, including LCD screens and OLED displays, can only handle strings or text. If you want to show sensor readings, calculations, or other numerical values on these displays, you must convert the integer to a string first.

int sensorValue = 42;

// Convert the integer to a string

String stringValue = String(sensorValue);

// Display the string on an LCD

lcd.print(stringValue);

In this example, the integer sensorValue is converted to a string (stringValue) before being displayed on an LCD [4].

Sending Data via Serial or Communication Modules

When you need to transmit data from your Arduino to other devices or systems through serial communication or communication modules like Bluetooth or Wi-Fi, it’s often more convenient to send data as strings. Converting integers to strings allows you to format and send data in a human-readable format that can be easily parsed and understood by the receiving end.

int temperature = 25;

// Convert the integer to a string

String dataToSend = String(temperature);

// Send the data via Serial

Serial.println(dataToSend);

In this case, the integer temperature is converted to a string (dataToSend) before sending it over the serial port.

Concatenating Text and Numerical Data

In many applications, you may need to combine text messages or labels with numerical data. When creating such composite messages, converting integers to strings becomes necessary to ensure that the text and data can be combined seamlessly.

int sensorReading = 42;

// Create a message by combining text and the integer

String message = “Sensor reading: ” + String(sensorReading);

// Display or send the message

Serial.println(message);

Here, the integer sensorReading is converted to a string and then combined with the text message “Sensor reading: ” to create a complete message.

Data Logging and File Writing

If your Arduino project involves data logging or writing data to external storage, such as an SD card, you often need to convert numerical values to strings. Text-based data files are easier to read and analyze, and converting integers to strings allows you to write data in a format that is readily accessible.

int humidity = 60;

// Convert the integer to a string and write it to a file

File dataFile = SD.open(“data.txt”, FILE_WRITE);

if (dataFile) {

dataFile.println(String(humidity));

dataFile.close();

}

In this example, the integer humidity is converted to a string and then written to a data file on an SD card.

Data Transmission Protocols

In some cases, when working with communication protocols like MQTT or HTTP, the data format expected by the receiving end may require numeric values to be presented as strings. Converting integers to strings ensures that the data conforms to the protocol’s requirements.

int soilMoisture = 35;

// Convert the integer to a string and send it via MQTT

String dataToSend = String(soilMoisture);

mqttClient.publish(“soil/moisture”, dataToSend);

In this scenario, the integer soilMoisture is converted to a string before being published via MQTT.

Methods To Convert Integer to String Arduino:

When working with Arduino, it’s common to encounter situations where you need to convert an integer to a string. This conversion allows you to work with both numerical and text-based data seamlessly, enabling you to display, transmit, or manipulate data as needed.

1) Using String() Function

The String() function is one of the most straightforward ways to convert an integer to a string in Arduino. This built-in function takes an integer as input and returns a string representation of that integer:

• Syntax: String String(int value);
• Parameters – value: The integer value that you want to convert to a string;
• Returns – a String object representing the integer value;

Example Code

Here’s an example of how to use the String() function to convert an integer to a string:

int sensorValue = 42;

// Convert the integer to a string using String() function

String stringValue = String(sensorValue);

// Print the result

Serial.println(“Sensor value as string:“ + stringValue);

In this code, the String(sensorValue) expression converts the sensorValue integer to a string, and the result is stored in the stringValue variable. You can then manipulate or display stringValue as needed.

2) Using sprintf() Function

The sprintf() function is a versatile function for formatting strings in Arduino. It allows you to create formatted strings by specifying placeholders for various data types, including integers. By using %d as a placeholder, you can convert an integer to a string within a formatted string:

• Syntax:int sprintf(char *str, const char *format, …);
• Parameters– str: A character array (string) where the formatted output will be stored;
• Format: A format string containing placeholders for various data types;
• “…”:Additional arguments that correspond to the placeholders in the format string;
• Returns:The number of characters written to the str array [5];

Example Code

Here’s an example of how to use the sprintf() function to convert an integer to a string within a formatted string:

int temperature = 25;

// Create a character array to store the formatted string

char formattedString[20]; // Adjust the array size as needed

// Use sprintf() to format the string with the integer value

sprintf(formattedString, “Temperature: %d°C”, temperature);

// Print the formatted string

Serial.println(formattedString);

In this code, the sprintf() function formats the string “Temperature: %d°C” by replacing %d with the value of the temperature integer. The resulting formatted string is stored in the formattedString character array.

3) Using dtostrf() Function

The dtostrf() function is particularly useful when you need to convert a floating-point number (e.g., a float or double) to a string with a specified number of decimal places.

It allows you to control the formatting of the floating-point value:

• Syntax: char* dtostrf(double val, int width, unsigned int precision, char* s);
• val: The floating-point value to be converted;
• width:The minimum width of the output string (including the decimal point and precision);
• precision:The number of decimal places to include in the output string;
• s:A character array (string) where the result will be stored;
• Return: A pointer to the resulting string (same as s);

Example Code

Here’s an example of how to use the dtostrf() function to convert a floating-point number to a string with a specified number of decimal places:

float humidity = 42.5;

// Create a character array to store the formatted string

char formattedString[20]; // Adjust the array size as needed

// Use dtostrf() to format the float value as a string with 1 decimal place

dtostrf(humidity, 6, 1, formattedString);

// Print the formatted string

Serial.println(“Humidity: ” + String(formattedString) + “%”);

In this code, dtostrf() is used to format the floating-point value humidity as a string with one decimal place. The resulting string is stored in the formattedString character array.

Summing up, converting an integer to a string is a common task in Arduino programming, and it’s essential to know multiple methods to accomplish this task:

• The String() functionis straightforward and convenient for converting integers to strings;
• The sprintf() functionoffers more control over string formatting and is suitable for complex formatting needs;
• The dtostrf() functionis ideal for converting floating-point numbers to strings with specific decimal places;

FAQ:

How to convert integer to char in Arduino?

To convert an integer to a character (char) in Arduino, you can use the char() function. Here’s an example:

int myInteger = 65;  // ASCII value of ‘A’

char myChar = char(myInteger);

In this example, myInteger is converted to the character ‘A’ and stored in myChar.

How to convert a variable to a string in Arduino IDE?

To convert a variable to a string in the Arduino IDE, you can use the String() function. For example:

int myValue = 42;

String myString = String(myValue);

This code converts the integer myValue to a string and stores it in myString.

How to convert character to string in Arduino?

You can convert a character to a string in Arduino using the String() constructor. Here’s an example:

char myChar = ‘A’;

String myString = String(myChar);

This code converts the character ‘A’ to a string and stores it in myString.

How to convert char input to string?

To convert a character input to a string in Arduino, you can directly use the String() constructor.

How to create a string in Arduino?

You can create a string in Arduino by declaring a variable of type String. For example:

String myString = “Hello, Arduino!”;

This code creates a string variable myString with the value “Hello, Arduino!”.

How to convert string to int and int to string?

To convert a string to an integer, you can use the toInt() method of the String class. For example:

String myString = “42”;

int myInt = myString.toInt();

To convert an integer to a string, you can use the String() constructor as mentioned earlier.

How to convert int and double to string?

You can convert both integers and doubles to strings using the String() constructor. Here’s an example:

int myInt = 42;

double myDouble = 3.14;

String intString = String(myInt);

String doubleString = String(myDouble);

How to convert string to double in Arduino?

To convert a string to a double in Arduino, you can use the toDouble() method of the String class. For example:

String myString = “3.14”;

double myDouble = myString.toDouble();

This code converts the string “3.14” to a double value.

Can I convert double to string?

Yes, you can convert a double to a string in Arduino using the String() constructor, as shown in previous examples.

Which function is used to convert a number to string?

In Arduino, you can use the String() constructor to convert various numerical types (int, double, etc.) to strings.

How to convert byte to string in Arduino?

You can convert a byte to a string in Arduino using the String() constructor in the same way as other numerical types. For example:

byte myByte = 65;  // ASCII value of ‘A’

String myString = String(myByte);

This code converts the byte myByte to a string and stores it in myString.

How do you create a string method?

In Arduino, you can create a custom string method by defining a function that operates on string data. Here’s an example of how you can create a simple string method to reverse a string:

String reverseString(String inputString) {

int length = inputString.length();

String reversedString = “”;

for (int i = length – 1; i >= 0; i–) {

reversedString += inputString.charAt(i);

}

return reversedString;

}

In this example, the reverseString function takes a string as input, iterates through its characters in reverse order, and builds a reversed string, which it returns.

You can call this custom method to reverse a string in your Arduino code:

String original = “Hello”;

String reversed = reverseString(original);

Serial.println(reversed);  // Outputs “olleH”;

This demonstrates how to create and use a custom string method in Arduino. You can define custom methods to perform various string operations based on your project’s requirements.

Useful Video: ADC39 – Convertir Integer to String || Arduino

References:

1. https://linuxhint.com/integer-to-string-arduino/
2. https://stackoverflow.com/questions/7910339/how-to-convert-int-to-string-on-arduino
3. https://www.best-microcontroller-projects.com/arduino-int-to-string.html
4. https://community.platformio.org/t/arduino-string-convert-int-to-string/33456
5. https://www.delftstack.com/howto/arduino/convert-integer-to-string-in-arduino/