1. ## Heap Sort

Hi everyone I am having a little problem with a heap sort code that I am writing. I have found a few templates that all looked the same but am having problems writing it on my own because I do not understand them completely. I completely understand how the heap sort algorithm works in theory and can draw out what happens using a binary tree. When implemented in code however I do not understand certain declarations like (root*2). I just wish I had a better picture of it. Please let me know if anyone can explain this or can direct me to a book or website that has an explanation of it.

Thanks

Code:
void heapSort(int numbers[], int array_size)
{
int i, temp;

for (i = (array_size / 2)-1; i >= 0; i--)
siftDown(numbers, i, array_size);

for (i = array_size-1; i >= 1; i--)
{
temp = numbers[0];
numbers[0] = numbers[i];
numbers[i] = temp;
siftDown(numbers, 0, i-1);
}
}

void siftDown(int numbers[], int root, int bottom)
{
int done, maxChild, temp;

done = 0;
while ((root*2 <= bottom) && (!done))
{
if (root*2 == bottom)
maxChild = root * 2;
else if (numbers[root * 2] > numbers[root * 2 + 1])
maxChild = root * 2;
else
maxChild = root * 2 + 1;

if (numbers[root] < numbers[maxChild])
{
temp = numbers[root];
numbers[root] = numbers[maxChild];
numbers[maxChild] = temp;
root = maxChild;
}
else
done = 1;
}
}

2. no time to explain now so just look over this applet