Pointers and Arrays - Basic question

[NorFredrik]

Hi I'm stuck wondering how an array assignment is legal.

num[i] equals *( num + i) equals *(i + num ) equals i[num]

It's the last assignment I'm unsure about, how can example 1[num] equals num[1]?
There is some grave lacking in my understanding about the C language, perhaps this is quite known logic?
Can somebody give me a reference to read up on when it comes to this specifically?

[maeriden]

Where did you learn it's equal? num[i] and i[num] are two very different things, starting from the fact that the first refers to an array called num and the second to an array called i.

[NorFredrik]

No no, i is not an array, it's simply an integer variable.
You can even forget the variable..

num[1] = 1[num] this is what boggles my mind..

For example the compiler internally converts num[1] into *(num+1)

[maeriden]

Oh yeah right. The square brackets are syntactic sugar for *(address + offset). So doing i[num] is like saying *(offset + address) which leads to dereferencing the same memory address as the first one.

[NorFredrik]

Ah, thank you very much. Seems a lot clearer now! :)
While I have the thread, do you know any C books which explains such topics?

[maeriden]

I don't know any book, I studied using the Kernighan&Ritchie but I didn't find it much newbie friendly. You can try googling 'pointer arithmetics' to get some more info on the subject.

[NorFredrik]

Ok, thank you for your help. I needed it ;)