Question

I came across this piece of code. In the cout statement the conditions evaluates to true.

   a[10][10]=’h’;
   cout<<(a[0]==*a)&&(*a==0[a]);

Accessing an array element/address using 0[a] is the new thing.
Can somebody please explain this type of notation ?

Answer 1

From http://c-faq.com/aryptr/joke.html

Q: I came across some joke code containing the expression 5[“abcdef”] . How can this be legal C?

A: Yes, Virginia, array subscripting is commutative in C. [footnote] This curious fact follows from the pointer definition of array subscripting, namely that a[e] is identical to *((a)+(e)), for any two expressions a and e, as long as one of them is a pointer expression and one is integral. The “proof” looks like

a[e]
*((a) + (e))    (by definition)
*((e) + (a))    (by commutativity of addition)
e[a]        (by definition)

This unsuspected commutativity is often mentioned in C texts as if it were something to be proud of, but it finds no useful application outside of the Obfuscated C Contest (see question 20.36).

Since strings in C are arrays of char, the expression “abcdef”[5] is perfectly legal, and evaluates to the character ‘f’. You can think of it as a shorthand for

char *tmpptr = "abcdef";

... tmpptr[5] ...