Arduino int

int

On the Arduino Uno (and other ATmega based boards) an 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). On the Arduino Due and SAMD based boards (like MKR1000 and Zero), 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).

int’s store negative numbers with a technique called (2’s complement math). The highest bit, sometimes referred to as the "sign" bit, flags the number as a negative number. The rest of the bits are inverted and 1 is added.

The Arduino takes care of dealing with negative numbers for you, so that arithmetic operations work transparently in the expected manner. There can be an unexpected complication in dealing with the bitshift right operator () however.

Syntax

Parameters

: variable name.
: the value you assign to that variable.

Sours: https://www.arduino.cc/reference/en/language/variables/data-types/int/

Arduino - Data Types



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.

voidBooleancharUnsigned charbyteintUnsigned intword
longUnsigned longshortfloatdoublearrayString-char arrayString-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 ASCII Char Table

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
Sours: https://www.tutorialspoint.com/arduino/arduino_data_types.htm
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why can Arduino variables of int type contain a value such as A2

You are correct. is just a number (like everything in a microcontroller). We can look at the corresponding part in (a file defined in the variants folder of your used core and of your used board, for me: ):

So here the core first defines the macro as 16 (which is the pin number of that pin) and then it declares a static constant with . So is just the pin number of that pin, in this case.

This is done to make the code more readable. The analog pins are marked with to , so it is good to also be able to refer to that with these names. If you wanted, you could also use the pin number directly. But that wouldn't be as easy to read.

answered Apr 28 at 12:29

chrislchrisl

11.9k22 gold badges1414 silver badges2323 bronze badges

Sours: https://arduino.stackexchange.com/questions/83833/why-can-arduino-variables-of-int-type-contain-a-value-such-as-a2

Data Types in Arduino

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Introduction

Computers, including the Arduino, tend to be highly data agnostic. At their core, the heart of the device is an arithmetic-logic unit (ALU), which performs (fairly) simple operations on locations in memory: R1+R2, R3*R7, R4&R5, etc. The ALU doesn't care what that data represents to a user, be it text, integer values, floating point values, or even part of the program code.

All of the context for these operations comes from the compiler, and the directions for the context get to the compiler from the user. You, the programmer, tell the compiler that this value is an integer and that value is a floating point number. The compiler, then, is left trying to figure out what I mean when I say "add this integer to that floating point." Sometimes that's easy, but sometimes it's not. And sometimes it seems like it should be easy, but it turns out to yield results you might not anticipate.

This tutorial will cover the basic data types available in Arduino, what they're typically used for, and will highlight the effects of using different data types on the size and performance speed of your programs.

Suggested Reading

You may want to familiarize yourself with a few concepts before we get started:

Defining Data Types

The Arduino environment is really just C++ with library support and built-in assumptions about the target environment to simplify the coding process. C++ defines a number of different data types; here we'll talk only about those used in Arduino with an emphasis on traps awaiting the unwary Arduino programmer.

Below is a list of the data types commonly seen in Arduino, with the memory size of each in parentheses after the type name. Note: signed variables allow both positive and negative numbers, while unsigned variables allow only positive values.

  • boolean (8 bit) - simple logical true/false
  • byte (8 bit) - unsigned number from 0-255
  • char (8 bit) - signed number from -128 to 127. The compiler will attempt to interpret this data type as a character in some circumstances, which may yield unexpected results
  • unsigned char (8 bit) - same as 'byte'; if this is what you're after, you should use 'byte' instead, for reasons of clarity
  • word (16 bit) - unsigned number from 0-65535
  • unsigned int (16 bit)- the same as 'word'. Use 'word' instead for clarity and brevity
  • int (16 bit) - signed number from -32768 to 32767. This is most commonly what you see used for general purpose variables in Arduino example code provided with the IDE
  • unsigned long (32 bit) - unsigned number from 0-4,294,967,295. The most common usage of this is to store the result of the function, which returns the number of milliseconds the current code has been running
  • long (32 bit) - signed number from -2,147,483,648 to 2,147,483,647
  • float (32 bit) - signed number from -3.4028235E38 to 3.4028235E38. Floating point on the Arduino is not native; the compiler has to jump through hoops to make it work. If you can avoid it, you should. We'll touch on this later.

This tutorial will NOT cover arrays, pointers, or strings; those are more specialized datatypes with more involved concepts that will be covered elsewhere.

Time and Space

The processor at the heart of the Arduino board, the Atmel ATmega328P, is a native 8-bit processor with no built-in support for floating point numbers. In order to use data types larger than 8 bits, the compiler needs to make a sequence of code capable of taking larger chunks of data, working on them a little bit at a time, then putting the result where it belongs.

This means that it is at its best when processing 8-bit values and at its worst when processing floating point. To demonstrate this fact, I've written a simple Arduino sketch which does some very simple math and can easily be altered to use different data types to perform the same calculations.

First, up, let's dump the code as-is into an Arduino Uno and see what results we get on the serial console.

Screen capture of the console doing a byte oriented add

Okay, lots of stuff there. Let's take things a bit at a time.

First, if you're following along, check the compiled size of the code. For addition with bytes, we end up with 2458 bytes of code. Not a lot, and, frankly, most of that is taken up with the serial output stuff. This data point will become important later on, however.

Next, let's look at the serial port output. What's the deal with the squares instead of a number for the printed variable values? That happens because the function changes the way it operates based on the type of data which is passed to it. For an 8-bit value (be it a or ), it will simply pipe out that value, in binary. The serial console is then going to try to interpret that data as an ASCII character, and the ASCII characters for 1, 2, and 3 are 'START OF HEADING', 'START OF TEXT', and 'END OF TEXT'. Hmm. Not particularly useful, are they, nor easy to display in one character? Hence the square: the serial console is throwing up its hands and saying, 'I don't know how to print this, so I made a square for you'. So, lesson one in Arduino datatype finesse: to get the decimal representation of an 8-bit value from , you must add the switch to the function call, like this:

Finally, observe the 'Elapsed time' measurement. Discounting the inaccuracies from using the function to measure elapsed time, which we'll do on all these tests, so we should get a very good RELATIVE measure of the time required for operations, if not a good absolute measure, you can see that adding two 8-bit values requires approximately 4 microseconds of the processor's time to achieve.

Testing Data Types (Addition)

Okay, let's move on to test some more data types. If you're following along at home, you'll want to change your code, as seen below:

Code snippet for byte programCode snippet for int code

Now, load the code onto your Arduino board. Check the compile size: 2488 bytes for versus 2458 bytes for . Not a lot bigger, but it IS bigger. Again, this is because using data types which require more than 8 bits of storage (like , , or also requires the compiler to generate more actual machine code for the addition to be realized - the processor itself simply doesn't have the capability of supporting larger data natively. Now, open the serial console and you should see something like this:

Addition with ints serial port capture.

Next observation: this time the values printed correctly. That's because the new datatype we've introduced, the , is correctly interpreted by the compiler as a numeric datatype, and correctly formats the output data to reflect that in the console. So, second lesson of Arduino datatype finesse: if you WANT to send the binary equivalent of a numeric datatype, say, as a means of sharing data with another computing device rather than a user looking at a console, use the function.

Next, let's check out "Elapsed time" again. We're up to 12 microseconds now - about 3 times as long! Still pretty short, but this is due to the previously mentioned fact that this is an 8-bit processor, so it needs to jump through some hoops to do 16-bit math, which is what's required when adding variables together.

Onward and upward! Now let's check out the datatype. Repeat the last code change, except this time replace the two incidents of with . Load the code and open your serial console and see what's happened.

Serial capture of addition with longs

Before we dive into the serial capture, let's revisit the compile size. I got 2516 bytes, this time- 28 bytes more than using and 58 more than using . Still a pretty small difference but a difference nonetheless, and a difference which could add up if you do a lot of math with instead of or .

Okay, now on to the serial results. Again, notice that the elapsed time changed. This time, however, it DECREASED from 12 microseconds to 8! How does that work? This is your third lesson in Arduino datatype finesse: what you think is happening may not be what is actually happening. I'm not sure why this occurs - it may be due to some compiler optimization, or due to some run-time optimization which saves time on small value additions which is not present in the int code. Regardless, is faster than is not necessarily a safe takeaway here, as we'll see when we get into multiplication and division.

Okay, last stop, floating point math. Floating point math on the Arduino is tricky because the Arduino lacks a floating point unit, which is fancy-talk for a dedicated section of the processor which handles math with an arbitrary number of digits after a decimal point. Floating point math is also a sticky concept, because while humans can deal well with arbitrary numbers of zeros after the decimal point, computers can't. This is the origin of the infamous 1 is not 1 bug that some early generation Pentium processors suffered from.

Alter the code as above again, but replace with in the two pertinent locations. Load the code and check out the compile size: 3864 bytes! What happened is that by including the floating point data type, you forced the compiler to include the floating point handling code. Clearly, that's a pretty big chunk of code - it increased the size by a fair margin. Datatype finesse lesson four: don't use floating point math unless you really, really have to. Most times, that's going to be limited to giving users feedback about something which is fairly meaningless as an arbitrary integer value: the ADC will return a value like 536, which is cryptic, but converted into floating point it would be something like 2.62V, which is much more useful.

Serial capture of addition with floating points

Now look at the run time on this code - back up to 12 microseconds. Also, note that the printed value now includes two zeros after the decimal place. If you want more (or fewer) digits after the decimal, you can add a number of digits into your print command:

Testing Data Types (Multiplication/Division)

Now let's look at what happens with 'harder' math - multiplication and division.

Here are some screen grabs for multiplication:

Multiply with bytes screen capture[(https://cdn.sparkfun.com/tutorialimages/datatypes/mult_int.jpg)
Multiply with bytes screen capture[(https://cdn.sparkfun.com/tutorialimages/datatypes/mult_float.jpg)

Check out the elapsed times: 4µs for , 8 for or , and 12 for - longer for larger data types, and also what we expect to see in terms of 'harder' math taking longer. Multiplication is still hardware supported, though - there is a native multiply instruction in the processor which makes multiply operations relatively easy. But what about division?

Divide with bytes screen captureDivide with ints screen capture
Divide with longs screen captureDivide with floats screen capture

Oh, my. division isn't too bad at 16µs, but 48 for ? Ouch. The problem here is that division does NOT have a native instruction in the Atmega instruction set, so the compiler has to do some back flips to create one. So, final lesson: not all mathematical operations are created equal. Divide takes a lot longer than multiply or add (or subtract, but that's really just add with a minus sign), and something like finding a square root or a sine would take even longer. So long, in fact, that it's often easier just to maintain a list of values for square roots or sine/cosine/tangent and look up the value that you want than it is to calculate it.

Resources and Going Further

I'm going to leave it here for now. I hope I've demonstrated clearly the benefits of using appropriate data types for your variables. The next tutorial will go into some of the really ugly pitfalls that are hiding in mixing data types and using INAPPROPRIATE data types - for instance, data types that are too small for the largest number that you may encounter.

All of the context for these operations comes from the compiler, and the directions for the context get to the compiler from the user. You, the programmer, tell the compiler that THIS value is an integer and THAT value is a floating point number. The compiler, then, is left trying to figure out what I mean when I say "add this integer to that floating point". Sometimes that's easy, but sometimes it's not. And sometimes it SEEMS like it SHOULD be easy, but it turns out to yield results you might not anticipate.

Here's some further reading you may want to explore with your new knowledge of data types:

Sours: https://learn.sparkfun.com/tutorials/data-types-in-arduino/all

Int arduino

unsigned int

Example Code

Notes and Warnings

When unsigned variables are made to exceed their maximum capacity they "roll over" back to 0, and also the other way around:

Math with unsigned variables may produce unexpected results, even if your unsigned variable never rolls over.

The MCU applies the following rules:

The calculation is done in the scope of the destination variable. E.g. if the destination variable is signed, it will do signed math, even if both input variables are unsigned.

However with a calculation which requires an intermediate result, the scope of the intermediate result is unspecified by the code. In this case, the MCU will do unsigned math for the intermediate result, because both inputs are unsigned!

Why use unsigned variables at all?

  • The rollover behaviour is desired, e.g. counters

  • The signed variable is a bit too small, but you want to avoid the memory and speed loss of long/float.

Sours: https://www.arduino.cc/reference/en/language/variables/data-types/unsignedint/

Reference   Language | Libraries | Comparison | Changes

int

Description

Integers are your primary data-type for number storage.

On the Arduino Uno (and other ATMega based boards) an 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).
On the Arduino Due and SAMD based boards (like MKR1000 and Zero), an 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).

's store negative numbers with a technique called 2's complement math. The highest bit, sometimes referred to as the "sign" bit, flags the number as a negative number. The rest of the bits are inverted and 1 is added.

The Arduino takes care of dealing with negative numbers for you, so that arithmetic operations work transparently in the expected manner. There can be an unexpected complication in dealing with the bitshift right operator (>>) however.

Example

int ledPin = 13;

Syntax

int var = val;
  • var - your int variable name
  • val - the value you assign to that variable

See Also

Reference Home

Corrections, suggestions, and new documentation should be posted to the Forum.

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.

Sours: https://www.arduino.cc/en/Reference.Int

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