Set Swap Counter to non-zero for bubble sort

Question

The pset 3 short on bubble sorting mentions that we should:

1) set a swap counter to a non-zero value.

2) Define the loop

3) In each loop iteration reset the counter to 0 and increase the swap counter if a swap of two array elements occurs.

4) after the loop if the swap counter is 0, terminate the sort

I understand the reason for this which is to stop the recursive bubble sort early if the data is sorted rather than running through up to n^2 loops.

However in my code I declare my swap counter and define it to be 0 rather than a non-zero value and it still seems to work. I don't find I need a non-negative value:

void sort(int array[], int size)
{
if (size <= 1)
    return;

int swapCounter = 0;    
for(int j = 0; j < size - 1; j++)
{

    if (array[j] > array[j + 1])
    {
        int swap = array[j + 1];
        array[j + 1] = array[j];
        array[j] = swap;
        swapCounter++;
    }
}

if (swapCounter > 0)
    sort(array, size - 1);
}

Is there something I am missing?

Do I need to set swapCounter to a non-zero integer before I define my for loop?

Or is this only neccessary when using do...while loops?

Answer 1

In the pseudo-code mentioned in the short swapcounter is used as a sentinel to detect whether swapping of two elements of the array has taken place in the current passing of the array. If the swapcounter is zero at the end of a particular iteration over the array elements this means that the array is already sorted.

Your implementation works in a similar way. You are checking if the swapcounter > 0 and then recursively calling the sort function with updated parameters, whereas the pseudo-code is taking swapcounter != 0 as a condition to continue the sorting process.

Since there is no way that the swapcounter could ever become negative so both the conditions ultimately lead to the same result. It has nothing to do with the usage of do..while loop.