What is radix sort?

#include <iostream>
using namespace std;
// utility function for printing the array.
void print(int arr[], int size) 
{               
	for(int i = 0; i < size; i++)
		cout << arr[i] << " ";
	cout << endl;
}
void RadixSort(int a[], int arraySize)
{
	// Initialize a bucket array and the starting LSD (digitPosition). 
	int i, bucket[arraySize], maxVal = 0, digitPosition = 1;
	
	// Find the maximum value in the array.
	// The number of passes in the algorithm will be
	// the number of digits the largest number has (maxVal).
	for(i = 0; i < arraySize; i++) 
	{
		if(a[i] > maxVal) 
			maxVal = a[i];
	}
	int pass = 1;  // used to show the progress
	/* This is the Count Sort algorothm: */
	while(maxVal/digitPosition > 0) {
		// digitCount[i] array will be counting the number 
		// of array values having that 'i' digit at their 
		// digitPosition-th place.  
		int digitCount[10] = {0};
		// Count the number of times each digit occurred at (digitPosition)th place in every input.
		for(i = 0; i < arraySize; i++)
			digitCount[a[i]/digitPosition%10]++;
		// Find cumulative count, so it now stores actual position
		// of the digit in the output array (bucket).
		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];
		/* End of Count Sort Algo */
		
		// At this point, the array is sorted by digitPosition-th digit 
		cout << "Pass #" << pass++ << ": ";
		print(a, arraySize);
		// Move to the next digit position, or next least significant digit.
		digitPosition *= 10;
	}   
}
 
// Driver code.
int main()
{
	int arr[] = {82, 901, 100, 12, 150, 77, 55, 23};
	int size = sizeof(arr)/sizeof(arr[0]);
	cout << "The unsorted array is: " << endl;
	print(arr,size);
	cout << endl;
	cout << "Starting Radix Sort: " << endl;
	cout << "Pass #0: ";
	print(arr,size);
	RadixSort(arr,size);
	return 0;
}