Hello!

I was wondering why the following C code compiles:

main()
{
int a[100];
int b= 4[a]; /* Looks like 4[a] is equivallent to a[4] ??? */
return b;
}

Any explanations/links that would me understand this would be
welcome (I coundn't find that in the C standard).
Cheers
g

g36130@googlemail.com wrote:
> Hello!
>
> I was wondering why the following C code compiles:
>
> main()
> {
> int a[100];
> int b= 4[a]; /* Looks like 4[a] is equivallent to a[4] ??? */
> return b;
> }
>
> Any explanations/links that would me understand this would be
> welcome (I coundn't find that in the C standard).

You could have found it in the C FAQ at http://www.c-faq.com/
It's question 6.11

On Feb 1, 1:04 pm, g36...@googlemail.com wrote:
> Hello!
>
> I was wondering why the following C code compiles:
>
> main()
> {
> int a[100];
> int b= 4[a]; /* Looks like 4[a] is equivallent to a[4] ??? */
> return b;
>
> }
>
> Any explanations/links that would me understand this would be
> welcome (I coundn't find that in the C standard).

You would better wonder why your code shouldn't compile.

main has to return int.
Evaluating uninitialized objects invokes undefined behavior.
As for your question, x[y] is equal to *(x + y), x+y == y+x.

<g36130@googlemail.com> wrote in message news
> I was wondering why the following C code compiles:
>
> main()
> {
> int a[100];
> int b= 4[a]; /* Looks like 4[a] is equivallent to a[4] ??? */
> return b;
> }
>
> Any explanations/links that would me understand this would be
> welcome (I coundn't find that in the C standard).
>
It's a silly quirk of the language.
Arrays can be treated as pointers in most contexts, and pointers as arrays.
a[4] = means *(a + 4). So it makes sense that 4[a] should mean *(4+a). But
to write that in code is rather pointless.

--
Free games and programming goodies.
http://www.personal.leeds.ac.uk/~bgy1mm

vippstar wrote:

> On Feb 1, 1:04 pm, g36...@googlemail.com wrote:
>> Hello!
>>
>> I was wondering why the following C code compiles:
>>
>> main()
>> {
>> int a[100];
>> int b= 4[a]; /* Looks like 4[a] is equivallent to a[4] ??? */
>> return b;
>>
>> }
> You would better wonder why your code shouldn't compile.
>
> main has to return int.
main() is equivalent to int main() in C90.
> Evaluating uninitialized objects invokes undefined behavior.
This doesn't mean it shouldn't compile.
--
Army1987 (Replace "NOSPAM" with "email")

"Malcolm McLean" <regniztar@btinternet.com> writes:
[...]
> Arrays can be treated as pointers in most contexts, and pointers as arrays.

Um, sort of. Read section 6 of the comp.lang.c FAQ to understand what
this really means.

--
Keith Thompson (The_Other_Keith) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"