Pretty Simple program.. huh… Output will be 0. 

Now if you replace arr[0] with 0[arr], the output would be same.
Because compiler converts the array operation in pointers before accessing 
the array elements. e.g. arr[0] would be *(arr + 0) and
therefore 0[arr] would be *(0 + arr) and you know that both *(arr + 0) and *(0 + arr) 
are same.