unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Memo1: TMemo;
    procedure Button1Click(Sender: TObject);
    procedure ShellSort(n :integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  AnArray :array[1..20] of integer;
  
implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
var i, j : integer;
begin
        {put a bunch of numbers into the array}

        Randomize;
        j := (sizeof(AnArray)) div (sizeof(integer));

        for i := 1 to j do
            AnArray[i] := Random(100);
        ShellSort(j); {pass array num elements to shellsort}
        For i := 1 to j do    {visual debugging}
           Memo1.Lines.Append(IntToStr(AnArray[i]));
end;

procedure TForm1.ShellSort(n : integer);  {n = num elements in array}
label  Jumpout;
var  g, h, i, j, value :integer;  s : string;
begin
      {visual debugging code, watch selection sort on memo
      comment this code out for large array sizes}
      s := '';
      for g := 1 to n do
         s := s + IntToStr(AnArray[g]) + ' ';
      Memo1.Lines.Append(s);

     {find the most efficient value for h}
     h := 1;
     repeat
          h := (3 * h) + 1;
     until (h > n);

     {shell sort}
     repeat
          h := h div 3;
          for i := h + 1 to n do begin
              value := AnArray[i];
              j := i;
              while (AnArray[j - h] > value) do begin
                   AnArray[j] := AnArray[j - h];
                   j := j - h;
                   if j <= h then goto Jumpout;
              end;
              Jumpout : AnArray[j] := Value;
          end;

          {visual debugging code, watch selection sort on memo
          comment this code out for large array sizes}
          s := '';
          for g := 1 to n do
             s := s + IntToStr(AnArray[g]) + ' ';
          Memo1.Lines.Append(s);


     until (h = 1);
end;
end.