c - With arrays, why is it the case that a[5] == 5[a]? -

as joel points out in stack overflow podcast #34, in c programming language (aka: k & r), there mention of property of arrays in c: a[5] == 5[a]

joel says it's because of pointer arithmetic still don't understand. why a[5] == 5[a]?

the c standard defines [] operator follows:

a[b] == *(a + b)

therefore a[5] evaluate to:

*(a + 5) 

and 5[a] evaluate to:

*(5 + a) 

a pointer first element of array. a[5] value that's 5 elements further a, same *(a + 5), , elementary school math know equal (addition commutative).