C: How do I change a variable's value by providing a memory address from scanf();
 

Hello, I want to change a variable's value by providing a memory address. Like in Commondore 64:
How can I get the variable memory location from scanf(); which the user will input it and edit the variable's value.
NOTE: I don't need the "split" thing to split and make it like a command prompt. Just ask for a variable's memory location.

Please explain simply. :)

well, when you define a variable
you can get it's address via
so address is the position in memory of the var
thus when you are doing this
you are moving to another memory space
and when you are doing this:
you are incrementing the value of var :)

so if you do something like
you can access to that memory area by *pointer (well you have to cast it to a type before because you cant deference a void* type ofc)
you can also do something like this if you feel more safe:
then you have to cast it for example

I hope you remember: it was POKE in BASIC.

Cast?

A cast is a "change of type"
This is a cast.
Obviously it doesn't always make sense

On an architecture where long is larger than pointer, you will corrupt the memory after &pointer on the stack.
If long is shorter than pointer, you will end up with garbage in pointer.

So instead you assume long and size_t are the same size ?!
That improves nothing.

I don't use scanf enough myself to have any confidence of the right answer.

johnsfine is right, there is not enough info to give a correct answer.

Note: in printf/scanf %zd/%zu might mean a pointer-sized integer (size_t, actually, but that should be compatible with uintptr_t)

The real question: how would the user know the address? Or they just enter random numbers and program interprets them as memory addresses?

No, actually johnsfine didn't do the right google search (and never uses C99) and didn't know the info NevemTeve just posted.

Now I know: If you are using a C99 compatible version of scanf, you can use %zu to read a decimal number directly into a pointer variable. I think you can rely on size_t being the same size as a pointer, even when you can't rely on long being the same size as a pointer.

I would have guessed the OP wanted to read the input in hex rather than in decimal, which I assume would be %zx, but the OP did not specify that (ask a better question in order to get a better answer).

I wondered about that as well. We get a lot of "how to" questions here, where you need to wonder whether the OP really ought to be doing the thing he asks how to do. It is often a close judgement call whether to answer "here is how" vs. "I think your plan to do that is based on a deeper misunderstanding".

I have not reviewed the C99 standard fully. I guess that is the answer then.