Comparing Sorts Program Help and Hints

1. Counting comparisons done in boolean expressions: You can take code like this:
   
   if (theArray[currentIndex] > theArray[indexSoFar])
   
   and turn it into code like this:
   
   if (++c_count && (theArray[currentIndex] > theArray[indexSoFar]))
   
   The expression "++c_count" takes care of incrementing the counter that tracks the number of comparisons. If you initialize counters correctly, the addition of expressions such as "++c_count" will not change the logic of the program. (Verify.)
   
   Notice that order is important here. It does not work to put "&& ++c_count" at the end of the original expression. (Why not?) Also it doesn't work right if you put "c_count++ &&" at the beginning of the original expression. (Why not?) If you are unsure of the answers to either of the foregoing questions, then review material about how Boolean expressions are evaluated in C++, and details about the difference between the values returned by ++x and x++.
   
   
2. Flushing Output: Use code like this:
   
   cout << "mergesort starting ... " ;
   cout.flush() ;
   mergesort(A, 0, howMany-1, cmpCount, mvCount) ;
   cout << "done" << endl ;
   
   to help the user see when the program starts and finishes each sort. If you don't use something like
   
   cout.flush()
   
   after
   
   cout << "mergesort starting ... " ;
   
   then the output may be buffered - which means you won't see this output on the screen
   
   "mergesort starting ..."
   
   until after the mergesort is completed!
   
   The endl in this statement
   
   cout << "done" << endl ;
   
   prints a newline character AND flushes the output, so you don't need to add a
   
   cout.flush()
   
   after cout << "done" << endl ;
   
   
3. Counter Data Types Big Enough For Big Numbers: It may be a good idea to make your counters unsigned long int. This will give you a little extra margin in case you come close to overflowing your counters. For example, you could declare your counters this way:
   
   unsigned long int cmpCount, mvCount ;
   
   Remember, when writing your code, to (re) initialize your counters when you start at new sort. It's an elementary, but common, mistake to start a new sort with a counter that has not been (re) initialized.
   
   
4. Sorting a Fresh Copy of the Original List Each Time: It is also an elementary observation, but one easily overlooked, that after you sort the list, it's not the original list any more - it has been sorted. So in this program, which is required to compare the performance of different sorting algorithms on the same input, you must arrange to give a "fresh" copy of the original input to each sorting algorithm. The usual way to do this is to keep one version of the list as an original and to make a new copy of the original each time you call for another sort. In C++, it's usually necessary to copy arrays by copying each slot, one at a time. Typically programmers do this with a for-loop.