I saw one example
int x = 10;
int y = 5;
bool isGreater = x > y;
printf("%d", isGreater);
But I could write this
int x = 10;
int y = 5;
printf("%d", x > y);
I am a complete beginner and I have no real reason why I would or would not want to deal with boolean variables, but I want to understand their raison d’être.
Edit: typo city
code is read more often that it is written. booleans are actually just integers under the hood but explicitly using booleans communicates your intent. you’re saying to the next guy that “if this is something other than 1 or 0 something has gone wrong”.
when it comes to C specifically, the bool type was a pretty late addition because as you say, an integer can do the job. but it’s very good for organisation, and it also allows the compiler to make some assumptions about how the variable can be accessed. if you know something can only be in two states, you can shove a whole bunch of them into the same byte of memory.
Thanks! I did indeed see a reference somewhere, saying that it makes the code easier to read too. :)
If u accidentally us the wrong type of variable it outputs en error when compiling. That’s one of the main pros of statically typed languages and why the most reliable scripts are written in them to my knollidge. I’m sure there a languages out there where u can us boolean as a int or float but non i know. Not that i would consider my self a programmer but i asked the myself the same questions when i started.
Sometimes you need to store a value that is either true or false and refer to it later or maybe update it. Maybe you have some complicated logic for when a loop needs to end that you can’t really represent in the while condition. You can make the while check your bool variable and then set it to false when you are ready to end. Perhaps you have a function that returns a bool value and you setup your logic so there is a default return value but you do some calculations and sometimes you want to return the other value. it lets you have a single return statement in the function which can be easier to read.
You use boolean variables in the same way as other variables. The example you share is indeed contrived. In that situation you need no variables at all. That example is merely showing the syntax.
Thank you for the explanation! Perhaps at my novice level, I should just go with it and learn the use of bool as I experience it. :)
Here’s a little secret: All data types don’t actually exist. When your code is compiled down to machine code your computer just operates on collections of bits. Types are a tool we use to make code more understandable to humans.
intandunsigned inttell us information about how numerical values are interpreted.booltells you that only two values are going to be used and that the value will somehow relate to true/false.chartells us that the value is probably some sort of text. But again, everything is just stored as bits under the hood.You can go even further and define new types, even though they might still just be numbers under the hood - you could for instance define a new type, e.g.
Age, which is still just an integer, but it tells you the reader more information about what it is and what it might be used for. You might define a new type just for error codes, so at a glance you can see that this function doesn’t return anint, it returns anOsError, even if the errors are actually still just integer values.C does however play somewhat loosely by these rules, and to try and ‘make your life easier’ will often ‘coerce’ types between eachother to make everything work. For instance, integer types can be coerced to booleans -
0isfalse, everything else istrue(even negative values). Later on you’ll find that arrays can ‘decay’ to pointers, and other fun surprises. Personally, I think this implicit coercion between types is one of C’s biggest mistakes. If types exist to help humans reason about code, what does it mean if the compiler needs to silently change types behind the scenes to make things work? It means the humans were sloppy and the compiler can only guess at what they actually wanted to do (and this is the best case scenario! What happens if the compiler coerces types in places humans didn’t expect? Bugs!).There exist a spectrum of different behaviours in this regard, some languages are what we call ‘weakly typed’ (like Javascript, or to a lesser extent C) and other languages which are ‘strongly typed’. Weakly typed languages will try to implicitly convert types together to make things work: In Javascript if you try and add an integer to text
"Hello!" + 52the compiler will try to implicitly convert types until something makes sense, for instance in this case the compiler would say ‘oh, they probably want to add the text “52” onto the end’ and will produce"Hello!52". Sometimes this is handy, sometimes it introduces bugs. A strongly typed language will instead simply refuse to compile until you make the types line up.I think there are several reasons. First, if you do it with an int, you’re probably using up 32bits per value. You’d need 1 but waste the other 31, they needlessly take up storage. (Edit: Though your bool will most likely take 8 bit anyways due to other things.) And then sometimes it’s nice to be expressive. So no one needs to remember if 1 is True or 0, or if True is greater than False, whether 2 or -1 map to True or False. And you end up in situations where either 2 equals 1, or True isn’t always equal True. Or you do weird things to handle values other than 0 and 1 in the operations. All of that can be avoided and the code gets more readable with specific types.
There’s nothing wrong with using ints, though. You just have to make sure the maths stays consistent.
Very nice point about the memory/storage usage! Also, I didn’t realize one can “map” other values as true/false than 1/0. But then again, I know very little at this moment. XD
Sure. As far as I remember in C, 0 is False. Every other number is True, you can use 1 or 42, doesn’t matter, they’re all “true”.
Except that a lot of the cstdlib functions return an int, where 0 == success, and negative numbers are falsy.
But I think one has to keep apart return codes that are signals to the OS and the end user, and 1/0 in a true/false context in conditional statements.
The way I make sense of it, is we sometimes return failure (i.e. from main). So 0 is no failure (aka success) and we can use the same thinking. The correct, expressive way to write it is probably use “EXIT_SUCCESS” and skip the ones and zeros. Pretty sure this comes from Unix. And with a lot of the other functions in cstdlib it’s the same way as using integers as booleans. For example a “malloc()” will either return your memory or a null pointer and the 0 is the special failure case.
But IMO the programming language shows its age and the context it was used in. More modern programming language design tends to be more strict with the types. Differentiate between interfacing with Unix stuff and other kinds of values. And we got more powerful concepts to deal with errors. So we don’t always have to abuse the zero to say we ended up in some special case.
Mallocreturn 0 is a failure, butopenreturn 0 is success. It’s just inconsistent, and it’s definitely an age and context thing.Rust’s
Resultapi are a pretty great solution. Not sure what other options are out there though.
Okay, now… variableA = 1 (true) and variableB = 42 (true). Suppose we want to compare the values of them to see if they’re the same or different. A simple check of
if variableA == variableBwill return False, because while they’re both set to ‘true’, they’re set to different values of ‘true’. It could get problematic and become a way to introduce really weird bugs.
Don’t be mislead by that comment. It implies that a boolean variable takes up 1 bit instead of 32. But most probably it will take 8 bits. You’re still “wasting” 7 bits instead of 31.
Good point. Yeah, my “probably” is doing a lot of heavy-lifting there. Thx, I’ve added a short sentence.) In reality we don’t really know the length of a bool nor an int type in C. Likely a bool is 1 Byte and an int is 4 Bytes. But that depends on the architecture and compiler. The bool it guaranteed to hold 0 and 1, so it must be at least 1 bit. But with how addressing works, it ends up being 8 bits (1 Byte) anyway. If we want to be more efficient than that, I believe we have to code something with bit fields. It’s a bit out of scope for a beginner, unless they do microcontroller stuff.
First, if you do it with an int, you’re probably using up 32bits per value.
One project I worked with stored boolean values as bits in an 8-bit int, and then used binary math to read and write individual bits from that int, with each bit representing a distinct and independent boolean variable.
Really weird, complicated, and sounds kind of dumb … but it worked, and it was extremely memory-efficient.
Oh hey I do this in jwts too.
I need to encode a lot of permissions
Don’t ask
C++ actually does this ‘optimisation’ for
std::vector<bool>. I say ‘optimisation’ because it effectively trades time for space, which is usually the opposite of what you want - space is cheap, time usually isn’t. Sometimes it’s a good tradeoff though - it’s common in embedded development where you might only have a few kB of RAM.
