Arduino Datatypes and Variables

Arduino Variables

In programming, we name the values that are stored for further processing with a single word called a variable. The value of a variable can change continuously (during runtime). The variable name should be chosen in such a way that it is easily readable and understandable within the program. In addition, a variable also has a data type that defines the value range.

The Variable must be declared before being used. So the data type, the variable name and the value of the variable are set. If no value is specified, the variable value is set to 0.

datatype Variable_Name = Value;

Example:

int motorSpeed = 255;

Comprehensible variable names such as motorSpeed or temperatureSensor improve the readability of the program.

Arduino Data types

A data type describes the value range and the possible operations of a variable. Since the data types of the variables require different amounts of memory, you should be aware of exactly which possible values the defined variable can have when creating the program: Is it only a digital state with the values yes and no or can the variable hold an entire text? You should select the variable data type accordingly. The most important data types and their value ranges for creating Arduino codes are listed below:

Data type	Range	Memory size	Explanation	Example
boolean	true/false	1 byte	Value for Yes/No or On/Off,	boolean machineStatus = true;
int	-32,768 to 32,767	2 bytes	Integer values for values without decimal places	int potiValue = 1023;
unsigned int	0 to 4,294,967,295	2 bytes	Integer for positive values without decimal places	int tempValue = -5;
byte	0 to 255	1 byte	Low values (and correspondingly small memory requirements)	byte brightnessLED = 126;
word	Unsigned 16-bit or 32-bit	16-bit on Atmega boards. 32-bit on Due and Zero	Be aware of processor used	word value = 1500;
long	-2,147,483,648 to 2,147,483,647	4 bytes	Integer numbers with big values	long offset = -15362;
unsigned long	0 to 4,294,967,295	4 bytes	Unsigned Integer numbers with big values	unsigned long secondsPassed = 45379;
float	-3.4028235E+38 to 3.4028235E+38	4 bytes	Values with decimal places	float voltageValue = 3.3;
double	-3.4028235E+38 to 3.4028235E+38	4 bytes	-3.4028235E+38 to 3.4028235E+38	double distanceGPS= 722.54;
char	-128 to 127	1 byte	Value for storing one character	char charR = ‘R’;
unsigned char	0 to 255	1 byte	Usually used with numbers having range 0 to 255	unsigned char charNumber = 255;
string	depends on definition	depends on need	Strings like texts or several characters	string brand[ ] = “ROBOSANS”;
array	depends to definition	Depends on array size	store values in variables with table form like e.g. lists of ports or configuration values	int portsPWM[ ] = {3,5,6,9,10,11};

In the following section we will summerize the datatypes in short.

Arduino sizeof

The Arduino sizeof function returns the number of bytes in a variable, or bytes an array occupies. Its syntax is:

sizeof(variable);

It returns the size of the variable/ array in number of bytes. The following sketch defines variables in various types and print the sizeof the variable on the serial monitor.

boolean boolVal;
int intVal;
unsigned int uintVal;
byte byteVal;
word wordVal;
long longVal;
unsigned long ulongVal;
float floatVal;
char charVal;
unsigned char ucharVal;

void setup() {

Serial.begin(9600);

Serial.print("Size of boolean in bytes = ");
Serial.println(sizeof(boolVal));

Serial.print("Size of int in bytes = ");
Serial.println(sizeof(intVal));

Serial.print("Size of unsigned int in bytes = ");
Serial.println(sizeof(uintVal));

Serial.print("Size of byte in bytes = ");
Serial.println(sizeof(byteVal));

Serial.print("Size of word in bytes = ");
Serial.println(sizeof(wordVal));

Serial.print("Size of long in bytes = ");
Serial.println(sizeof(longVal));

Serial.print("Size of unsigned long in bytes = ");
Serial.println(sizeof(ulongVal));

Serial.print("Size of float in bytes = ");
Serial.println(sizeof(floatVal));

Serial.print("Size of char in bytes = ");
Serial.println(sizeof(charVal));

Serial.print("Size of char in bytes = ");
Serial.println(sizeof(ucharVal));
}

void loop() {
}

The resulting sizeof variables in byte on the serial monitor is:

Arduino sizeof array

To get the size of array, use the function sizeof with the array name inside as follows

int myArray[] = {11, 12, 13, 14, 15, 16, 17, 18};
int arraySize = sizeof(myArray);

Arduino length of array

To get the length of an array, divide the number of bytes present in the given array with the number of bytes in the array data type as follows

int myArray[] = {11, 12, 13, 14, 15, 16, 17, 18};
int arrayLength = sizeof(myArray) / sizeof(int);

Do you want to learn more? you can read these articles down below.

16×2 LCD Interfacing With Arduino

DHT11 Humidity And Temperature Sensor

Interfacing 7 Segment Display with Arduino

Sources:

arduino.cc