Data types in C refers to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in the storage and how the bit pattern stored is interpreted.
The following table provides all the data types that you will use during Arduino programming.
| void | Boolean | char | Unsigned char | byte | int | Unsigned int | word |
| long | Unsigned long | short | float | double | array | String-char array | String-object |
void
The void keyword is used only in function declarations. It indicates that the function is expected to return no information to the function from which it was called.
Example
Void Loop ( ) {
// rest of the code
}
Boolean
A Boolean holds one of two values, true or false. Each Boolean variable occupies one byte of memory.
Example
boolean val = false ; // declaration of variable with type boolean and initialize it with false boolean state = true ; // declaration of variable with type boolean and initialize it with true
Char
A data type that takes up one byte of memory that stores a character value. Character literals are written in single quotes like this: ‘A’ and for multiple characters, strings use double quotes: “ABC”.
However, characters are stored as numbers. You can see the specific encoding in the ASCII chart. This means that it is possible to do arithmetic operations on characters, in which the ASCII value of the character is used. For example, ‘A’ + 1 has the value 66, since the ASCII value of the capital letter A is 65.
Example
Char chr_a = ‘a’ ;//declaration of variable with type char and initialize it with character a Char chr_c = 97 ;//declaration of variable with type char and initialize it with character 97
unsigned char
Unsigned char is an unsigned data type that occupies one byte of memory. The unsigned char data type encodes numbers from 0 to 255.
Example
Unsigned Char chr_y = 121 ; // declaration of variable with type Unsigned char and initialize it with character y
byte
A byte stores an 8-bit unsigned number, from 0 to 255.
Example
byte m = 25 ;//declaration of variable with type byte and initialize it with 25
int
Integers are the primary data-type for number storage. int stores a 16-bit (2-byte) value. This yields a range of -32,768 to 32,767 (minimum value of -2^15 and a maximum value of (2^15) – 1).
The int size varies from board to board. On the Arduino Due, for example, an int stores a 32-bit (4-byte) value. This yields a range of -2,147,483,648 to 2,147,483,647 (minimum value of -2^31 and a maximum value of (2^31) – 1).
Example
int counter = 32 ;// declaration of variable with type int and initialize it with 32
Unsigned int
Unsigned ints (unsigned integers) are the same as int in the way that they store a 2 byte value. Instead of storing negative numbers, however, they only store positive values, yielding a useful range of 0 to 65,535 (2^16) – 1). The Due stores a 4 byte (32-bit) value, ranging from 0 to 4,294,967,295 (2^32 – 1).
Example
Unsigned int counter = 60 ; // declaration of variable with type unsigned int and initialize it with 60
Word
On the Uno and other ATMEGA based boards, a word stores a 16-bit unsigned number. On the Due and Zero, it stores a 32-bit unsigned number.
Example
word w = 1000 ;//declaration of variable with type word and initialize it with 1000
Long
Long variables are extended size variables for number storage, and store 32 bits (4 bytes), from -2,147,483,648 to 2,147,483,647.
Example
Long velocity = 102346 ;//declaration of variable with type Long and initialize it with 102346
unsigned long
Unsigned long variables are extended size variables for number storage and store 32 bits (4 bytes). Unlike standard longs, unsigned longs will not store negative numbers, making their range from 0 to 4,294,967,295 (2^32 – 1).
Example
Unsigned Long velocity = 101006 ;// declaration of variable with type Unsigned Long and initialize it with 101006
short
A short is a 16-bit data-type. On all Arduinos (ATMega and ARM based), a short stores a 16-bit (2-byte) value. This yields a range of -32,768 to 32,767 (minimum value of -2^15 and a maximum value of (2^15) – 1).
Example
short val = 13 ;//declaration of variable with type short and initialize it with 13
float
Data type for floating-point number is a number that has a decimal point. Floating-point numbers are often used to approximate the analog and continuous values because they have greater resolution than integers.
Floating-point numbers can be as large as 3.4028235E+38 and as low as -3.4028235E+38. They are stored as 32 bits (4 bytes) of information.
Example
float num = 1.352;//declaration of variable with type float and initialize it with 1.352
double
On the Uno and other ATMEGA based boards, Double precision floating-point number occupies four bytes. That is, the double implementation is exactly the same as the float, with no gain in precision. On the Arduino Due, doubles have 8-byte (64 bit) precision.
Example
double num = 45.352 ;// declaration of variable with type double and initialize it with 45.352
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