unit Unit1 interface uses Windows Messages SysUtils Variants Classes G

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Memo1: TMemo;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    function SubNumStrings (Str1, Str2 : string): string;
    function AddNumStrings (Str1, Str2 : string): string;
    function MultiplyNumStrings (Str1, Str2 : string): string;
    function factorial(var n : integer) : string;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}


function TForm1.AddNumStrings (Str1, Str2 : string): string;
var
  i : integer;
  carryStr : string;
  worker : integer;
  workerStr : string;
begin
  Result := inttostr (length(Str1));
  Result := '';
  carryStr := '0';

  // make numbers the same length
  while length(Str1) < length(Str2) do
    Str1 := '0' + Str1;

  while length(Str1) > length(Str2) do
    Str2 := '0' + Str2;

  i := 0;
  while i < length(Str1) do
  begin
    worker := strtoint(copy(Str1, length(str1)-i, 1)) +
              strtoint(copy(Str2, length(str2)-i, 1)) +
              strtoint (carryStr);
    if worker > 9 then
    begin
      workerStr := inttostr(worker);
      carryStr := copy(workerStr, 1, 1);
      result := copy(workerStr, 2, 1) + result;
    end
    else
    begin
      result := inttostr(worker) + result;
      carryStr := '0';
    end;


    inc(i);
  end; { while }
  if carryStr <> '0' then
    result := carryStr + result;
end;



function TForm1.SubNumStrings (Str1, Str2 : string): string;
var
  i : integer;
  carryStr : string;
  worker : integer;
  workerStr : string;
begin
  Result := inttostr (length(Str1));
  Result := '';
  carryStr := '0';

  // make numbers the same length
  while length(Str1) < length(Str2) do
    Str1 := '0' + Str1;

  while length(Str1) > length(Str2) do
    Str2 := '0' + Str2;

  i := 0;
  while i < length(Str1) do
  begin
    worker := strtoint(copy(Str1, length(str1)-i, 1)) -
              strtoint(copy(Str2, length(str2)-i, 1)) +
              strtoint (carryStr);
    if worker < 0 then
    begin
       workerStr := inttostr(worker + 10);
       carryStr := '-1';
       result := workerStr + result;
    end
    else
    begin
       result := inttostr(worker) + result;
       carryStr := '0';
    end;


    inc(i);
  end; { while }
  if carryStr <> '0' then
    result := carryStr + result;
end;


function TForm1.MultiplyNumStrings (Str1, Str2 : string): string;
var
  i, j : integer;
  carryStr : string;
  worker : integer;
  workerStr : string;
  tempResult : string;
begin
  Result := '';
  carryStr := '0';
  tempResult := '';

  // process each digit of str1
  for i := 0 to length(Str1) - 1 do
  begin
    while length(tempResult) < i do
      tempResult := '0' + tempResult;

    // process each digit of str2
    for j := 0 to length(Str2) - 1 do
    begin
      worker := (strtoint(copy(Str1, length(str1)-i, 1)) *
                 strtoint(copy(Str2, length(str2)-j, 1))) +
                strtoint (carryStr);
      if worker > 9 then
      begin
        workerStr := inttostr(worker);
        carryStr := copy(workerStr, 1, 1);
        tempResult := copy(workerStr, 2, 1) + tempResult;
      end
      else
      begin
        tempResult := inttostr(worker) + tempResult;
        carryStr := '0';
      end;
    end; { for }
    if carryStr <> '0' then
      tempResult := carryStr + tempResult;
    carryStr := '0';

    result := addNumStrings (tempResult, Result);
    tempResult := '';
  end; { for }

  if carryStr <> '0' then
    result := carryStr + result;
end;



function TForm1.factorial(var n : integer) : string;
var i : integer;
    r : string;
begin
    r := '1';
    for i := 2 to n do
        r := MultiplyNumStrings(r, IntToStr(i));
    factorial := r;
end;

procedure TForm1.Button1Click(Sender: TObject);
var a ,b : integer;
begin
    a := 70;
    b := 50;
    Memo1.Text := SubNumStrings( factorial(a), factorial(b)) ;
end;

end.