What is this java post increment operator doing?

So there's a piece of an radix sort implemented Java code that reads as below:

aux[count[a[i]]++] = a[i];

Why use a post increment operator? Why not aux[count[a[i]]+1]? Is the post increment simply to increment the value in count[a[i]] by 1 and store it there?

radixSort.java

int N = a.length;
int[] count = new int[R+1];
for (int i = 0; i < N; i++)
  count[a[i]+1]++;
for (int r = 0; r < R; r++)
  count[r+1] += count[r];

for (int i = 0; i < N; i++)
  aux[count[a[i]]++] = a[i];
for (int i = 0; i < N; i++)
  a[i] = aux[i];
Jon Skeet
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quotationmark

Is the post increment simply to increment the value in count[a[i]] by 1 and store it there?

Yes, exactly. There are two side-effects of the statement: one is a modification to an element of aux, and the other is a modification to an element in count.

Personally I'd avoid writing it like that - I'd probably write:

// We don't use i other than to index into a, so use an
// enhanced for loop instead
for (int value : a)
{
    aux[count[value]] = value;
    count[value]++;
}

Note that even if the change to count weren't required, aux[count[a[i]]+1] wouldn't do the same thing - because aux[count[a[i]]++] refers to the element in aux with index count[a[i]], before the increment, because ++ is being used as a post-increment here.

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