Sort in descending order

[cppnoob7331]

How do I implement this sorting algorithm in descending order without using vector library or std::reverse? I tried to change the signs using trial and error but it's either my program crashed or the sort was not working at all. I was comparing the process time of some sorting algorithms.

  void radixSort(int *a, int arraySize)
{
int i, bucket[arraySize]; //Using c++ VLA extension
int maxVal = 0;
int digitPosition =1;
	for(i = 0; i < arraySize; i++)
	{
		if(a[i] > maxVal)
            maxVal = a[i];
	}

	int pass = 1;  // used to show the progress
	/* maxVal: this variable decide the while-loop count
	           if maxVal is 3 digits, then we loop through 3 times */
	while(maxVal/digitPosition > 0) {
		/* reset counter */
		int digitCount[10] = {0};

		/* count pos-th digits (keys) */
		for(i = 0; i < arraySize; i++)
			digitCount[a[i]/digitPosition%10]++;

		/* accumulated count */
		for(i = 1; i < 10; i++)
			digitCount[i] += digitCount[i-1];

		/* To keep the order, start from back side */
		for(i = arraySize - 1; i >= 0; i--)
			bucket[--digitCount[a[i]/digitPosition%10]] = a[i];

		/* rearrange the original array using elements in the bucket */
		for(i = 0; i < arraySize; i++)
			a[i] = bucket[i];
		/* move up the digit position */
		digitPosition *= 10;
	}
 }

Any help will be gladly appreciated

[keskiverto]

I don't know what your function does, but isn't the principle of radix-sort to distribute input into bins in such manner that when you read the bins in order, you get a sorted output? If so, the data in the bins is sorted (ascending) and you simply need to read the bins in reverse order to get the descending output.

[cppnoob7331]

Unfortunately, I do not know how to understand the radix sort because I'm just a beginner in c++ and I am only comparing the time complexity of sorting algorithms. I only knew how to do the bubble, selection, and bucket sort.

[keskiverto]

If you don't understand an algorithm, then you cannot implement it efficiently, and then performance comparisons are unreliable, aren't they?

Algorithms are abstract, language-independent logic. The different sorts are described (somewhere). How to write the logic in language X is semi-separate issue.