C secara tradisional digunakan #defines untuk konstanta. That last sentence is not accurate. From a general programming point-of-view, const variables are usually preferable (where possible). What is the main difference between these when naming a variable? A byte stores an 8-bit unsigned number, from 0 to 255. C/C++ are considered lower-level languages than scripting languages like Python. Macros don't have scope, which increases the chance of naming conflicts. Is what I am about to say correct? The maximum positive value of an "int" depends on the compiler. In general, it is preferred to use const over #define, for defining constants. It will often require an explicit cast before it will behave differently (although there are various situations where it can safely be implicitly type-promoted). Note that #define DEF ABCDEFG I was very careful to use the term "expression" in what I said. But today and especially for something like a simple value, a const int would generally be preferred over a #define as it can be safer to avoid #define so you can avoid some silent issues. But, if your 'const int' is declared but not defined, it doesn't. If I'm understanding your question correctly, you are trying to see if you can use the string "AKB73575431", to create a variable with the same name AKB73575431, and assign the value of AKB_LEN to it. But today and especially for something like a simple value, a const int would generally be preferred over a #define as it can be safer to avoid #define so you can avoid some silent issues. Ahh, my mistake. If it is not used in an array, then it will probably not save any RAM at all - generally const variables (which don't involve pointers) are simply optimised into 'ldi' instructions wherever they are used - much like #defines. That's a construct I use often. How close am I? They will both generate exactly the same machine code (depending on some compiler optimisations). Memory usage: #define vs. static const for uint8_t, ESP8266 stops working when I use 2x static const char(PROGMEM), Use chars in quotes in const char* as name of function. pcbbc: Long story short: CONST s are handled by the compiler, where as #DEFINE s are handled by the pre-processor. You can't set array sizes using const int. It compiles fine for me (after correcting the ']' vs. '}' typo). You would use 'constexpr' like you would use 'const', except that this tells the compiler that the value MUST be known to the compiler at compile time. It's not quite correct to say that a compile-time constant uses no storage though, because its value still has to occur in code (i.e. int ledPin = 13 In this way it acts like a '#define' - since the value is known to the compiler, no storage need be allocated for it. In general, in C++ (which Arduino is based on), the best way to define constants is Continue Reading The reverse is also possible, although probably less common. In 1.0.5/1.5.3 and greater, you only get error messages. What is the difference between keywords const and readonly in C#? econjack: but you can not change the assigned value of ledpin throught out its scope. One thing is that you test for the symbols existence during compilation if it created with a #define using conditionals Is replaced with Indeed, a lot of Arduino code is very C like though. all throughout the program and the compiler will know what to do with them. pin numbers. You can add -std=c++11 to platform.txt for now (1.5.7). Not the answer you're looking for? If it sees in your program a non-const variable is never modified, it may actually treat it as a constant, never putting it into RAM. #define asks the preprocessor to do a literal text-wise copy paste into the code before the compiler even sees it.. #defined values have no type, which prevents the compiler from throwing warnings for various code issues.. const int theoretically consumes RAM, however compiler optimizations will often annul any RAM usage if the variable is only used in one file and you never take its address . You will get a compiler error if you try to assign a value to a const variable. This is going to introduce confusing compiler messages and a difficult to locate bug MisterG: This yields a range of -32,768 to 32,767 (minimum value of -2^15 and a maximum value of (2^15) - 1). 'const' is just a hint for the compiler. pYro_65: To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How can I use a VPN to access a Russian website that is banned in the EU? . Personally I would suggest beginners steer clear of it. #define 123.456 * 789_DEF 654.123 Unlike general purpose computing, memory is obviously at a premium when dealing with something like an Arduino. Find centralized, trusted content and collaborate around the technologies you use most. econjack: I am looking for the source and/or proper definition for the int() function. const variables are considered variables, and not macro definitions. You would create a Remote class, and the Remote might have different members such as name, mfr, and power: Then you can access data of it with things like AKB.mfr, AKB.power. Time to switch to UECIDE! You raise some excellent points (especially about the array limits -- I hadn't realised the standard compiler with Arduino IDE supported that yet). They take up program memory space, and have a type (which is advantageous in many situations). i.e. In C++ const have internal linkage by default and there's no point in declaring them static. 'const int' (and it's relatives) have some uses, but there are subtle pitfalls with them. PROGMEM This is likely why James says they can introduce hard-to-find bugs. bool doIHaveTheThing[COUNT_OF_THINGS] = {false, false, false, false, false]; // Doesn't compile! Why use static_cast(x) instead of (int)x? Is this an at-all realistic configuration for a DHC-2 Beaver? It's possible to get the benefits of type-safety while also storing the data in program space (Flash). The other way is to use the const keyword, like. and their level of experience I stand by my statement and judgement that they do not need to be confused by a full explanation at this point. I need an efficiant way to define el cdigo HTML, que es convertido en componentes nativos de interfaz, esto es llamado el VirtualDOM (Jimenez, 2019) . It is easy to accidentally forget to declare the constant as "long". A static variable declared within a function is basically a global variable that the compiler won't let other parts of the code access. Counterexamples to differentiation under integral sign, revisited. MisterG: BE SURE to check when moving between target machines and compilers. Furthermore, you could also make the Remote class without the name member, and store remotes in a map container: Now if you want to access a remote called "AKB" from the map, you can do things like: Thanks for contributing an answer to Stack Overflow! I'm thinking of having a separate file for each controller and I want to use a #define statement in each header to ensure that I get good separation of each signal name. It can be used in C++, but there are better ways. Bracers of armor Vs incorporeal touch attack, Disconnect vertical tab connector from PCB, Sudo update-grub does not work (single boot Ubuntu 22.04). static limits the variable's scope and means its memory will only be initialized once. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This genereates an error: char *c = 500; Its the normal integral conversions which allow them to be converted and assigned, and the same rules apply regardless of weather whether the integer is a literal, variable, or constant. While the compiler must use some default data type in the preprocessor pass, it's the resolution of that expression that makes it seem to be typeless. Description The const keyword stands for constant. The compiler will replace references to these constants with the defined value at compile time. // It doesn't work well, because you can't use it in many situations where the compiler wants a 'real' constant. Effectively, this implies that the pointer shouldn't point to some other address. No. How to convert a std::string to const char* or char*. If you write "int a = 5;" that defines a variable with an initial value of 5 (and then you can set it to anything you want). Such why I would for assigning to my Arduino UNO. Arduino Stack Exchange is a question and answer site for developers of open-source hardware and software that is compatible with Arduino. True, but it can assume the resolved data type used in the expression. vs What are constants? is there a way to detect that a macro argument is really a #define constant vs just a variable that has been declared "const"?--- bill. Guide to the C++ language constexpr keyword. This means that the variable can be used just as any other variable of its type, but its value cannot be changed. So in the header I have this signal for the power button on a remote: Some of you might recognise this data format as cribbed straight from the tutorials on IRLib2. While the compiler must use some default data type in the preprocessor pass, it's the resolution of that expression that makes it seem to be typeless. If you've done sufficient Arduino programming, you'd have seen that there are two ways of defining constants. Agree Help us identify new roles for community members. And if you have another remote, with a different name, you would need to create a whole new macro function, to get them to work. Memory usage Using const int i_variable_for_whatever does NOT use memory under ant circumstances that I have encountered so far. Description. For example, in many cases the compiler is required to allocate storage for these values, even though they never change! Powered by Discourse, best viewed with JavaScript enabled. What I want to do is construct the variable or #define name from a string and then use that. Is there any reason on passenger airliners not to have a physical lock between throttles? When novices try to use #define we end up with code like and many other heinous misunderstandings of what they are doing. OP- If you are still with us XC32 sees it as a variable that does not change, but as variables can change, even if they can't, they are no good as used above. Affordable solution to train a team and make them project ready. It exists at all times, not just when the function is called and so takes a constant amount of memory. If you ask it nicely, it will provide warnings. Better way to check if an element only exists in one array. For example, when using pull-up resistors on my buttons, I usually do this: As for #2, the compiler is pretty smart. Is a const int Is a const byte The compiler know when it can fit a number into one register and when it can't. However it is good practice to use coding that indicates your intent. #define is a pre-processor directive, essentially a sort of macro. Is it important to declare it as such? It's hard to get the variable name you created, as they are hidden under macros. The difference is that #define is processed by the preprocessor doing what amounts to simple text replacement. This means that the variable can be used just as any other variable of its type, but its value cannot be changed. Ready to optimize your JavaScript with Rust? I've been Googling dereferencing variables in C++ but keep getting pages on pointers. program memory rather than SRAM) anywhere that it's used. The constants in Arduino are defined as the predefined expressions. const int consumes RAM and has a type and a memory address, so you can pass &variable into functions that take a pointer to const int, and the compiler will complain if you put it somewhere that's not supposed to be an int.. #define asks the preprocessor to do a straight text-replace before the compiler ever sees any of your code, and so it doesn't consume RAM or have a type or a memory address. Gives And it took AGES to figure it out. Defined constants in arduino don't take up any program memory space on the chip. The value of true and false are defined as 1 and 0. The keyword "const" tells the compiler that a variable (or pointer) can not be modified. Or is it a matter of choice? C But I'll try again. If you find this answer helpful please upvote the answer so other people will also take benefit from it. Should I give a brutally honest feedback on course evaluations? So, I started looking at consts. What can we do with questions 'bumped' by Community bot? 'constexpr' is always defined at declaration, so if the name is visible it is usable. True, but compiling with the default settings for the IDE is alarmingly quiet, and those are the settings that most newbies use. Learn more, Difference between #define and const in Arduino, Difference between #define and const in C. What is the difference between #define and const Keyword in C++? If you used a define, you would not have a proper type to give e, and would have to use an integer. This is a great example of why #define shouldn't be used. char *search ( char *s, char *t ); searchs t ts. Say if you want to create multiple variable with prefix AKB_, such as AKB_len, AKB_power, AKB_mfr. Is it better to use #define or const int for constants? For example for the number 0, the binary form is 00000000, there are 8 zeros (8 bits in total). const int ci_max_encoder_clicks = 80 ; To learn more, see our tips on writing great answers. Really? I think the map suggestion is the most likely answer, but I've been struggling to get it to work on the Arduino. And I believe reference and dereference are not the terms you are looking for. Since (2) is apparently an option, you don't . To learn more, see our tips on writing great answers. You can even use them for some amount of namespace control. The best answers are voted up and rise to the top, Not the answer you're looking for? Debuggers like Visual Studio's don't let you. You can't initialize a const with another const. If anyone cares, #define X Y causes the preprocessor to do a replacement of any symbol X in your code to symbol (s) Y before the code is run through the compiler. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. You can't create a variable name based on values from another string. in C++? Any non-zero integer is determined as true in terms of . - Bald Engineer, http://arduino.cc/forum/index.php/topic,86800.15.html, to will let the compiler complain if your program tries to modify a value. How does legislative oversight work in Switzerland when there is technically no "opposition" in parliament? const restricts your ability to modify the value. Log in or register to post comments; Top. and. This is different from const int X = Y; which goes directly into the compiler. You will get a compiler error if you try to assign a value to a const variable. Expanding on your example a little: int size = 10000; const int size2 = 10000; int main () { size = 1; // fine size2 = 2; // won't compile } In this case, that means size2 really is a constant. CGAC2022 Day 10: Help Santa sort presents! It is a variable qualifier that modifies the behavior of the variable, making a variable " read-only ". Appealing a verdict due to the lawyers being incompetent and or failing to follow instructions? It is a variable qualifier that modifies the behavior of the variable, making a variable " read-only ". On the Arduino Uno (and other ATmega based boards) an int stores a 16-bit (2-byte) value. Physically, as far as the Arduino is concerned there is absolutely no difference. On an 8-bit microcontroller with 2,048 bytes of RAM, resources matter. define and const are not technically the same thing, but they do accomplish the same goal. It affects both the program size and the variable space. Moreover, I always like to have my pin definitions up at the top all in one place, so the question becomes which type of const would be appropriate for a pin defined as A5. Difference between const int*, const int * const, and int const * in C. Difference between const int*, const int * const, and int const * in C/C++? rev2022.12.9.43105. I have seen -32767 to 32767 (which i thought was 'short int') and -2147483648 to 2147483648. const int ledPin = 13. It is typeless in that it can be used in almost any expression where a data type is used and the compiler won't flag it as a type mismatch where a cast would normally be required. means that when you use DEF you'll get XYZDEFG not ABCDEFG, once I knew that, I was far more careful, but still used defines instead of consts Difference between signed and unsigned integer in Arduino. 2) #define is not scope controlled whereas const is scope controlled How can I use a VPN to access a Russian website that is banned in the EU? Also note that . I have one, too, but I want it to run an arduino in a project I've not thought of yet! Using a const variable vs. a #define can affect where the data is stored in memory, which may force you to use one or the other. Now, I understand that #define is really a "search an replace" type of thing, looking for ledPin and replacing it with 13. Well, to my surprise, Most often, an int is two bytes (32767 max) or four bytes (>2 billion max). For example: Even in the Hello World "blink" sketch I have seen the following: #define ledPin = 13 @bperrybap "static const" vs "#define" in c When I do this : #define WEEKDAYS 7 and that : const int WEEKDAYS = 7; Any difference between them ? Arduino IDE 1.5.7 now has gcc 4.8.1 and C++11 will be turned on in 1.5.8. How do I parse a string to a float or int? 4. #define MAX_ENCODER_CLICKS, double d_pi_clicks = cd_pi_value * ci_max_encoder_clicks ; The IDE itself still has a way to go, but its improving. I guess they base it on the fact newbies can't understand the messages spewed out. double d_pi_clicks = double(PI_VALUE) * double(MAX_ENCODER_CLICKS) ; BE SURE to check when moving between target machines and compilers. for the number 255, the binary form is 11111111. 2 KB and 32 KB respectively for the Uno). static const : "static const" is basically a combination of static(a storage specifier) and const(a type qualifier). It depends on what you need the value for. Asking for help, clarification, or responding to other answers. First you can utilize macros. 'int' is manly used as a counter, but my main issue is what is the max value for this variable? Personally I would suggest beginners steer clear of it. const int promedio = 30; const int intervalo = 30000; //30seg const int intervalo_minimo = 10000; . Do you mean if you can use the substring, I simple way to do it is to write a script (ksh, awk, python) to parse it and write the code for you. What is the main difference between these when naming a variable? It can catch some types of programming errors or typos. the compiler will try place the variable in RAM if it can fit in a register. const int boolSize = Data [0].BoolSize; so what i want is, i dont want to predefine the boolean size in the cpp code. Integer constants are numbers that are used directly in a sketch, like 123. compiles without error, but assigning 500 into a byte probably isn't going to work. Unless you take their address or declare them extern, they will generally just have a compile time existence. You can even see that it is there by issuing: xxd test | grep ONE_E The first and most obvious is that it means a value is read-only. If you roll the clock back say 30 years, things like const types and inline functions didn't exist so the use of macros was actually necessary. As pointers on a machine that has 16-bit addressing will be 2 bytes wide, the differences by using #define and const int are negligible, just in access time (SRAM is faster). But since #define is a pre-processor feature, it can be used for so much more. int *const is a constant pointer to integer This means that the variable being declared is a constant pointer pointing to an integer. How to set a newcommand to be incompressible by justification? Is this possible and if so, can someone give me an example? you end up with var being 14464 instead of 80000, This ensures that the value is not truncated to 16 bits. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. (In my way of thinking, anyway, it can get confused) Say if you want to create multiple variable with prefix AKB_, such as AKB_len, AKB_power, AKB_mfr. Connect and share knowledge within a single location that is structured and easy to search. I think I wasn't clear enough in that I don't want to "create" the variable. They are . My question is can I parse the string in the "key" value and use the substring: Failing that, is it possible to change the define to a global int and dereference it instead? I am having issues with my int reaching the max value of 32767 and am looking for an alternative. The difference is that const int creates a variable, and #define is a macro in the language, it swaps out the word with the number whenever it is encountered. Macros can get very sophisticated especially if using some of the more advanced pre-processor capabilities like concatenation or pasting. const int . Arduino adalah hibrida aneh, di mana beberapa fungsionalitas C ++ digunakan di dunia yang disematkan biasanya lingkungan C. Memang, banyak kode Arduino sangat C seperti. double() is required, or it doesn't calculate correctly, When compiled, the version with consts uses the same variable storage memory, and LESS programming space It looks like "const int" is a good habit to get into for when I get on to more difficult code and, eventually, writing my own. The implications for this specifically are a few bytes of memory. Variables defined using const, on the other hand, are just normal variables, whose values can't be changed. Description The const keyword stands for constant. sketch_jul17a.ino:5:18: warning: overflow in implicit constant conversion declares a variable, not a pointer. const int isnt a variable, it is a constant. Does balls to the wall mean full speed ahead or full speed ahead and nosedive? Would salt mines, lakes or flats be reasonably found in high, snowy elevations? However, there are many other situations where there isn't necessarily a single 'correct' answer. The first line ( static const int.) I'm glad my daughter is using the Raspberry Pi at the moment. Most importantly, they can't be used in very common situations where #define DOES work, for example as the size of an array. I'm putting together an Arduino sketch to send out raw infrared signals to emulate IR controllers. Its too quiet to tell you the truth, some warnings would be useful. There are, however, times when the fact that a symbolic constant is typeless can be a good thing (e.g., when working with a union). Hence its much better they steer clear of #define. 1) #define is pre-processor directive while const is a keyword #define is used to define some values with a name (string), this defined string is known as Macro definition in C, C++ while const is a keyword or used to make the value of an identifier (that is constant) constant. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. you are creating a variable (ledpin) of int data type and assigning 13 to it. Enjoy unlimited access on 5500+ Hand Picked Quality Video Courses. Because a #define is a textual replacement, it is "typeless". I have been programming professionally since 1978, and could see NO reason to use const instead of define, based on my experience and reading of the documentation. Most often, an int is two bytes (32767 max) or four bytes (>2 billion max). The term "const" informs the compiler a pointer or variable can't be changed. . Thanks again :). If I understand you correctly, using #define IS NOT strong typing because it uses the default data type, but by defining a "const" variable as an 8-bit unsigned integer (const uint8_t) you are telling the compiler what to use and not letting the pre-processor make that default determination. What is the difference between const int*, const int * const, and int const *? Asking for help, clarification, or responding to other answers. #define INPUTS DDRD = 0x00 Is that true const int memory usage is less than normal int. const int * const And int const * const are the same. Hence its much better they steer clear of #define. Then if you change pins then each use would need to be changed. There are simply no reasons to prefer #define over const, aside from few exceptions. It makes the code easy to read. I use const int to define an integer variable that is not allowed to change. I want to be able to quit Finder but can't edit Finder's Info.plist after disabling SIP. Its value is set at compile time and cant be changed. Making it const makes it clear that the number won't change, and making it byte (or uint8_t) makes it clear that you are expecting a small number. Plus, if you look at my answer below, I demonstrate that there are circumstances when you don't really know which type to use, so. The disadvantage of #define is that is replaces . Should teachers encourage good students to help weaker ones? Theres nothing you can do with #define that you cant do by writing the code out longhand (or by using const int/long/whatever). A #define is a preprocessor macro, not a variable. AND it is MUCH MUCH easier to ensure that calculations are type converted properly BE SURE to check when moving between target machines and compilers. I agree. For Digital pin numbers contained in variables, either can work - such as: But there is one circumstance where I always use #define. So, what should we use for Arduino? Making statements based on opinion; back them up with references or personal experience. Const values defined like this are not visible for the actual compiler, while a variable defined with the const modifier is an actual typed "variable" (well not really that variable). For some applications, it's quite easy to run out of SRAM, so it can be helpful to shift some things into Flash. Variables in C programming language, which Arduino uses, have a property called scope. @MHotchin We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. pcbbc: You (and everyone else so far) omitted the third alternative: static const int var = 5; #define var 5. enum { var = 5 }; Ignoring issues about the choice of name, then: If you need to pass a pointer around, you must use (1). It looks like "const int" is a good habit to get into for when I get on to more difficult code and, eventually, writing my own. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, I'm having hard time to understand what you were trying to do. #define Es un macro que se ejecuta antes de la compilacin. It is a variable qualifier that modifies the behavior of the variable, making a variable " read-only ". I hadn't seen "const byte" used in the (limited number of) examples I've seen, but I can see how it will save RAM in a bigger application. Is it important to declare it as such? Well, not really. In general, it is preferred to use const over #define, for defining constants. Its too quiet to tell you the truth, some warnings would be useful. I often like this because: So in an idiomatic C++ program, there is no reason whatsoever to use #define to define an integer constant. #define PI_VALUE 3.14159 The compiler will replace references to these constants with the defined value at compile time. Why use an int variable for a pin when const int, enum or #define makes much more sense, How to Store the results from a Ping Sensor in a variable. Using #define for compile time constants is a hold-over from the C programming language. constexpr also doesn't have some of the disadvantages that preprocessor macros have(learncpp): Thanks for contributing an answer to Arduino Stack Exchange! We make use of First and third party cookies to improve our user experience. There are many things you can do with macros that cannot be done with variables or writing out code longhand as macros are text substitution done on the source code before the compile is run. This can hypothetically result in ambiguities, because the type may end up being resolved differently depending on how/where it's used. Connect and share knowledge within a single location that is structured and easy to search. Its not type less at all, literal integers are a type of int, and will never be char/unsinged char, only character literals can be chars. You can't create a variable name based on values from another string. bool doIHaveTheThing[COUNT_OF_THINGS] = {false, false, false, false, false]; // Doesn't compile! I did a write up here, with a simple explain of how much RAM is used (checked with avr-size) when using const and when not: Arduino boards have microcontrollers with notoriously small amounts of RAM. I am scratching my head on this as well. #include <stdio.h> #define MAXS 30 char *search ( char *s, char *t . And if you are writing your code in C++ you can use. c++ arduino Share Improve this question Follow The big advantage of const over #define is type checking. Normally, integer constants are treated as base 10 (decimal) integers, but special notation (formatters) may be used to enter numbers in other bases. The main reason for that is type-safety. Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company. This is obviously different from a '#define', which is straight textual substitution. Most often, an int is two bytes (32767 max) or four bytes (>2 billion max). At the very least, the compiler can (if configured correctly) emit a more reliable warning when a type issue occurs. That means it impacts available Flash for any type that takes up more space than a pointer. // It doesn't work well, because you can't use it in many situations where the compiler wants a 'real' constant. In that case, the compiler would print 1 instead of ONE_E. For variables of a specified type which are not altered during execution, either can usually be used. Its the normal integral conversions which allow them to be converted and assigned, and the same rules apply regardless of weather the integer is a literal, variable, or constant. An int can be modified when you need, it is read/write and a const int is read only. Avoid using #define (a text-based symbol substitution) until you understand the problems that can arise when using it. But in regard to the OPs questionand their level of experience I stand by my statement and judgement that they do not need to be confused by a full explanation at this point. Everything was working, I added a few new functions, and started getting strange results in functions that had been working before, and nothing had changed. 37Arduino37 . Its a mistake if you ask me, some warnings will point out logic errors which will compile fine. Gives a compile error (already defined, because ABC is replaced with XYZ in the second line), #define ABC XYZ It only takes a minute to sign up. Since (2) is apparently an option, you don't need to pass pointers around. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Kind of defeats the verbose output mode, the last error is always shown. Python offers simplicity, but at the cost of run-time resources. At least that way you get a proper build environment - and can even change the compiler options if you want. However, the compiler should complain when it assigns a "larger" data type into a "smaller" data type (e.g., byte = int) and it doesn't. Is it possible to hide or delete the new Toolbar in 13.1? The other example works without. Similarly, in some situations you're forced to use variables, such as when you need an array of values (i.e. Cada una de ellas tiene su explicacin. MisterG: Here are some guidelines which I would follow: Type safety Variables defined using const, on the other hand, are just normal variables, whose values can't be changed. The new way of doing things for C++ is a relatively new mechanism call 'constexpr'. const has a number of effects in C++. #define ABCDEF QWERTY This is SO much more complicated than Python With complexity comes power. They take up program memory space, and have a type (which is advantageous in many situations). A #define (preprocessor macro) directly copies the literal value into each location in code, making every usage independent. http://arduino.cc/forum/index.php/topic,86800.15.html, Well, not really. EDIT: microtherion gives an excellent answer which corrects some of my points here, particularly about memory usage. const int COUNT = 3; does not define a macro; it defines a name of a variable, and wherever that variable is used, the value 3 is used. It compiles fine for me (after correcting the ']' vs. '}' typo). Ready to optimize your JavaScript with Rust? Arduino C++ Dereference a #define or const int? 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