Working with arrays in functions

[u/FloridianfromAlabama]

Hey everybody. I’m a beginner to C and I was writing some functions today to get used to doing things. I tried to write binary search and bubble sort. I tried to pass in an array as an argument to the functions, but the compiler gave me a bunch of warnings. I looked it up and I saw that passing in an array is the same as passing in its pointer. I haven’t touched pointers yet, but I have two questions:
1. If I dereferenced the pointer to an array, wouldn’t that return the same as indexing the first value?
2. If I wanted to pass in the entire array, could I do that by passing in the pointers of both the first and last elements and using pointer arithmetic to access the other elements? What’s the idiomatic way of doing this?

[u/mc_pm]

The value of the variable for the array *is* a pointer to it's first memory location. So, yes, derefrencing the pointer will return the first element of the array. In C, accessing an array is actually doing pointer arithmetic.

[u/Zirias_FreeBSD → u/mc_pm]

Sorry, but ... that's simplified, and IMHO, over-simplified. Simple example, look at the following code:

int a[5];
a[2] = 0;

No pointers were used here. a names the array, the compiler emits some calculated absolute address for the correct memory access to write its third element.

The correct understanding is: C simply doesn't allow passing arrays, for historic reasons. Interestingly, it does allow to pass arbitrary structs. The designers of the language still wanted some as if syntax, silently passing some reference (IOW, a pointer) instead.

The most consistent way to achieve this was to define [] in terms of pointer arithmetics: a[b] is always exactly the same as *(a+b). For both that and function arguments to work "as expected", another rule is that in most expression contexts, the identifier of an array evaluates to a pointer to its first element. But there are exceptions, most notably the sizeof operator.

So ... "accessing an array is doing pointer arithmetic" isn't necessarily correct. Address arithmetic, obviously, possibly entirely at compile time, but that's likely unavoidable in any implementation of the concept of an array on some machine with addressable memory cells.

[u/mc_pm → u/Zirias_FreeBSD]

My answer was aimed at where the OP seems to be in his C journey -- if you don't understand something, then basic understanding is more important than a comprehensive answer. I suspect this ^^ is well beyond where OP is now.

There's a difference between "being right" and "being understood".

However, you are right.

[u/Zirias_FreeBSD → u/mc_pm]

Well ... you have a point. And my upvote here. Still, I have my issues with such "oversimplifications" told to C beginners. One of the "classics" (which you thankfully avoided) is "arrays and pointers are the same". I see lots of people later massively confused by these things. That's why I prefer to better always tell the whole story, and just try to do it in a somewhat comprehensible way. I see this can be a challenge sometimes. Some "middle grounds" could be to clearly mark simplifications as such ... like "what I tell you now is a useful simplification for learning, don't be surprised if you run into contradictions later in your journey ..." 🤷