Thread: Sorting/Dynamic Array's

Hey hey,

So I've encountered a weird problem that I am not sure how to work around. I'm trying to calculate distances between particles in a system, store them in an array, sort it, and extract certain information from it. However, my distance array contains no zeros before the sort, yet after the first element is always 0. I don't think it's the sorting algorithm as it works fine on other arrays, but I have included it anyway.

Code:

void quickSort(double *arr, int elements) {
	
#define  MAX_LEVELS  300
	
	int  beg[MAX_LEVELS], end[MAX_LEVELS], i=0, L, R;
	float swap, piv;
	
	beg[0]=0; end[0]=elements;
	while (i>=0) {
		L=beg[i]; R=end[i]-1;
		if (L<R) {
			piv=arr[L];
			while (L<R) {
				while (arr[R]>=piv && L<R) R--; if (L<R) arr[L++]=arr[R];
			while (arr[L]<=piv && L<R) L++; if (L<R) arr[R--]=arr[L]; }
			arr[L]=piv; beg[i+1]=L+1; end[i+1]=end[i]; end[i++]=L;
			if (end[i]-beg[i]>end[i-1]-beg[i-1]) {
				swap=beg[i]; beg[i]=beg[i-1]; beg[i-1]=swap;
			swap=end[i]; end[i]=end[i-1]; end[i-1]=swap; }}
		else {
		i--; }}}
/* End QuickSort()  */

Here is where I think the problem is, and I feel like it has something to do with the indexing of the array but I can't seem to fix it.

Code:

	for(k = 0; k < 1; k++){
		
		SIZE = NUM_A-k-1-1;
		rA = (double *)malloc(SIZE * sizeof(double));
		printf("Size = %d\n", SIZE);

		for (i=k+1; i < NUM_A; i++ ){
			
			//if (k==i){continue;}
			
			rx = (x[k] - x[i])- Lx*rintl((x[k] - x[i])/Lx);
			ry = (y[k] - y[i])- Ly*rintl((y[k] - y[i])/Ly);
			rz = (z[k] - z[i])- Lz*rintl((z[k] - z[i])/Lz);
			
			rA[i] = sqrt( rx*rx + ry*ry + rz*rz);
			printf("r[%d][%d] = %lf\n", k, i, rA[i]);
			
		}
		
		quickSort(rA, SIZE);
		printf("Sorted\n");
		
		for(i = 0; i < SIZE; i++){ printf("r[%d][%d] = %lf\n", k, i, rA[i]); }

I have a good reason for that, however, in thinking deeper about your comment it is true that I need to do this a different way.

I just figured it out thanks to that.

Thanks!
Paddon

Your sorting algorithm is correct, but some of the data types don't make sense.
You're swapping ints using the 'swap' variable which is of type float.
You've storing a double value from the array as a float value in the pivot 'piv'. That may cause it to sort incorrectly for values that are different as doubles, but close enough to appear equal as floats.