// SHELSORT.CPP. This implements the Shell sort for parallel arrays
//               containing CSC course coes and the number of students
//               in each course.
// For: CSC250
// By:  DR. Menuge.

#include <iostream>

using namespace std;

void Load_Arrays       ( int[], int[], int &);
void Shell_Sort_Lists  ( int[], int[], int  );
void Print_Lists       ( int[], int[], int  );
const int MaxElement =  15;

int main ()
{
  int         CourseNumberList         [MaxElement];
  int         StudentNumberList        [MaxElement];

  int ListLength;

  Load_Arrays       (CourseNumberList, StudentNumberList, ListLength);
  Print_Lists       (CourseNumberList, StudentNumberList, ListLength);
  Shell_Sort_Lists  (CourseNumberList, StudentNumberList, ListLength);
  Print_Lists       (CourseNumberList, StudentNumberList, ListLength);
  
  return 0;

} // end main


void Load_Arrays ( int CourseNumberList[], int StudentNumberList [ ],
                   int &listsize)
{
  int I = 0,
      CourseNum = 0; // sentinel variable

  // priming read:
  cout << "Enter the CSC course number e.g. 150 (0 to quit) " << endl;
  cin >> CourseNum;

  while ( (CourseNum != 0) && (I < MaxElement)) {

         CourseNumberList  [I] = CourseNum;
         cout << "Enter the number of students in the course " << endl;
         cin >> StudentNumberList[I];
         I++;
         // read next:
         cout << "Enter the CSC course number e.g. 150 (0 to quit) " << endl;
         cin >> CourseNum;

   } // end while

   listsize = I;

} // end load arrays







void Shell_Sort_Lists ( int CourseNumberList[], int StudentNumberList [ ],
                        int listsize)

{
  bool
   Swap;
  int
   Gap,
   Limit,
   LastElement,
   I,
   TempCourse,
   TempStudents;

   LastElement = listsize-1;

   Gap = LastElement / 2;

   while (Gap > 0) {

       Swap = true;
       while (Swap) { //do passes at this size gap until a pass with
                      //no swaps.

          Swap  =  false;  //stays false unless swap occurs 
          Limit =  LastElement - Gap;

          for (I = 0; I <= Limit; I++)
              if (CourseNumberList[I] > CourseNumberList[I + Gap]) { // swap
                  TempCourse                   = CourseNumberList  [I];
                  TempStudents                 = StudentNumberList [I];
                  CourseNumberList  [I]        = CourseNumberList  [I + Gap];
                  StudentNumberList [I]        = StudentNumberList [I + Gap];
                  CourseNumberList  [I + Gap]  = TempCourse;
                  StudentNumberList [I + Gap]  = TempStudents;
                  Swap                         = true;
               } // end swap

       } // end inner while

       Gap = Gap / 2;  // halve gap

    } // end outer while

} // end Shell Sort lists

void Print_Lists ( int CourseNumberList[], int StudentNumberList [ ],
                   int listsize)
{
  cout << endl << "The lists are as follows: " << endl;
  cout << "Course:   Students:" << endl << endl;
  for (int I= 0; I < listsize; I++)
      cout << CourseNumberList[I] << "\t" << StudentNumberList[I] << endl;

} // end Print Lists.