unit SLDUnit;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, LResources, Forms, Controls, Graphics, Dialogs,
  StdCtrls, contexthelpunit;

type

  { TSLDepFrm }

  TSLDepFrm = class(TForm)
    HelpBtn: TButton;
    ResetBtn: TButton;
    ComputeBtn: TButton;
    ReturnBtn: TButton;
    CostEdit: TEdit;
    SalvageEdit: TEdit;
    PeriodsEdit: TEdit;
    DepreciationEdit: TEdit;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    procedure ComputeBtnClick(Sender: TObject);
    procedure FormShow(Sender: TObject);
    procedure HelpBtnClick(Sender: TObject);
    procedure ResetBtnClick(Sender: TObject);
    function SLNDepreciation(Cost, Salvage: Extended; Life: Integer): Extended;
  private
    { private declarations }
  public
    { public declarations }
  end; 

var
  SLDepFrm: TSLDepFrm;

implementation

{ TSLDepFrm }

procedure TSLDepFrm.ResetBtnClick(Sender: TObject);
begin
     CostEdit.Text := '';
     SalvageEdit.Text := '';
     PeriodsEdit.Text := '';
     DepreciationEdit.Text := '';
end;

procedure TSLDepFrm.FormShow(Sender: TObject);
begin
     ResetBtnClick(self);
end;

procedure TSLDepFrm.HelpBtnClick(Sender: TObject);
begin
  ContextHelpForm.HelpMessage((Sender as TButton).tag);
end;

procedure TSLDepFrm.ComputeBtnClick(Sender: TObject);
VAR
      Cost, Depr, Salvage : Extended;
      Life : integer;

begin
     // Obtain results

     Cost := StrToFloat(CostEdit.Text);
     Salvage := StrToFloat(SalvageEdit.Text);
     Life := StrToInt(PeriodsEdit.Text);
     Depr := SLNDepreciation(Cost, Salvage, Life);
     DepreciationEdit.Text := FloatToStr(Depr);
end;

function TSLDepFrm.SLNDepreciation(Cost, Salvage: Extended; Life: Integer): Extended;
{ Spreads depreciation linearly over life. }
begin
  if Life < 1 then ShowMessage('ERROR in SLNDepreciation - Life < 1');
  Result := (Cost - Salvage) / Life
end;

initialization
  {$I sldunit.lrs}

end.