p20_Kenna

unit main_u;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ComCtrls;

type
  TForm2 = class(TForm)
    Label1: TLabel;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    function stringMultiply(a, b : string) : string;
    function stringAdd(a, b : string) : string;
  public
    { Public declarations }
  end;

var
  Form2: TForm2;

implementation

{$R *.dfm}

{ TForm2 }

procedure TForm2.FormCreate(Sender: TObject);
var
  sprod : string;
  i, isum : integer;
  start, freq, stop: int64;
begin

  QueryPerformanceFrequency(freq);
  QueryPerformanceCounter(start);

  sprod := '1';

  for I := 2 to 100 do
    begin
      sprod := stringMultiply(sprod, inttostr(i));
    end;

  isum := 0;

  for I := 1 to length(sprod) do
    begin
      isum := isum + strtoint(sprod[i]);
    end;

  QueryPerformanceCounter(stop);
//  ShowMessage(FloattostrF((stop - start) / freq, ffNumber, 10, 3)); // Solution time will be shown upon program completion.

  ShowMessage(inttostr(isum));
  Label1.Caption := FloattostrF((stop - start) / freq, ffNumber, 10, 3);
end;

function TForm2.stringAdd(a, b: string): string;
var
  i, j, alen, blen, carry, itotal : integer;
  stemp : string;
begin
  if (length(a) < length(b)) then
    begin
      stemp := a;
      a := b;
      b := stemp;
    end;

  // append the 0's to keep the peace
  alen := Length(a);
  blen := Length(b);

  for I := 1 to (alen - blen) do
     begin
      b := '0' + b;
     end;

  carry := 0;
  stemp := '';

  // perform the addition
  for I := alen downto 1 do
      begin
        itotal := strtoint(a[i]) + strtoint(b[i]);

        itotal := itotal + carry;

        carry := itotal div 10;
        itotal := itotal mod 10;

        stemp := inttostr(itotal) + stemp;
      end;

  result := stemp;
end;

function TForm2.stringMultiply(a, b: string): string;
var
  alen, blen : integer;
  i, j, carry, curprod : integer;
  stemp, stotal : string;
begin

  alen := Length(a);
  blen := length(b);

  stotal := '';

  for I := blen downto 1 do
      begin
        carry := 0;
        stemp := '';
        for j := alen downto 1 do
          begin
            // find product from current pointers
            curprod := strtoint(a[j]) * strtoint(b[i]);
            curprod := curprod + carry;

            // adjust carry
            if (curprod > 9) then
              begin
                carry := curprod div 10;
                curprod := curprod mod 10;
              end
            else carry := 0;

            // append to the tempString
            stemp := IntToStr(curprod) + stemp;
          end;

          // position multiplier
          for j := 1 to blen - i do
              begin
                stemp := stemp + '0';
              end;

          // find the string total

          stotal := stringAdd(stotal, stemp);
      end;

  stotal := inttostr(carry) + stotal;
  result := stotal;
end;

end.