shell sort pseudocode to C++ code - c++

Question

# Sort an array a[0...n-1].
gaps = [701, 301, 132, 57, 23, 10, 4, 1]
foreach (gap in gaps)
# Do an insertion sort for each gap size.
for (i = gap; i < n; i += 1)
temp = a[i]
for (j = i; j >= gap and a[j - gap] > temp; j -= gap)
a[j] = a[j - gap]
a[j] = temp
this is the pseudocode in Wikipedia page.
I'm not sure about that if my c++ code is correct according to it. Here is my code:
void shellSort(int *array, int array_size)
{
int e, i, j, temp;
for(e = 0; e < array_size; e++)
{
for( i = e; i < array_size; i++)
{
temp = array[i];
for( j = i; j >= e && array[j - e] > temp; j -= e)
{
array[j] = array[j-e];
}
array[j] = array[temp];
}
}
}
And here is my test code:
int main()
{
int sizes[9] = {9,3,5,7,1,0,6,2,4};
int size = 0;
shellSort(sizes,size);
for(int i=0;i<size;i++)
{
cout << sizes[i] << endl;
}
return 0;
}
but it shows nothing on the screen.

Answer 1

Okay, let's take this from the top
void shellSort(int *array, int array_size)
{
Your code completely omitted the needed gaps array
const int gaps[] = {701, 301, 132, 57, 23, 10, 4, 1};
int e, i, j, temp;
The outer loop needs to be across gaps rather than 0 to array_size
for(e = 0; e < sizeof(gaps)/sizeof(int); ++e)
{
int gap = gaps[e];
You need to use the gap from the gaps array in the inner loop
for( i = gap; i < array_size; ++i)
{
temp = array[i];
for( j = i; j >= gap && array[j - gap] > temp; j -= gap)
{
array[j] = array[j-gap];
}
You need to store temp back into the array
array[j] = temp;
}
}
}
NB: I don't have a compiler to hand right now, so I haven't checked that, but I think it's right.
Also, a few minor points, this:
int e, i, j, temp;
is bad practice, instead declare each variable as you use it, i.e. do this instead:
for( int i = gap; i < array_size; ++i)
{
int temp = array[i];

Answer 2

For some reason (no comments were given), my first answer was deleted (typo - you set size to 0, not 9). The question wondered why "it shows nothing on the screen". If you set size to 0, what do you expect a for loop to do when it iterates from 0 to < size???
Before looking at the algorithm, your parameters must be correct. Start there. If SOMETHING now gets dumped to the screen, NOW you can start debugging the algorithm (if the output was wrong). If the output is right, then your algorithm is probably okay.
If I am wrong about this, PLEASE POST A COMMENT TO MY ANSWER. Don't just "delete" it!?!