unit Main;

interface

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

type
  TForm1 = class(TForm)
    edtQty: TEdit;
    Label1: TLabel;
    edtPrice: TEdit;
    Label2: TLabel;
    edtExVat: TEdit;
    btnCost: TButton;
    Label3: TLabel;
    Label4: TLabel;
    edtVat: TEdit;
    Label5: TLabel;
    edtVatInc: TEdit;
    btnAdd: TButton;
    btnClear: TButton;
    btnSubTotal: TButton;
    btnCancel: TButton;
    btnClearMemory: TButton;
    edtChange: TEdit;
    edtCash: TEdit;
    btnChange: TButton;
    Label7: TLabel;
    Label6: TLabel;
    procedure btnCostClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure btnAddClick(Sender: TObject);
    procedure btnSubTotalClick(Sender: TObject);
    procedure btnClearClick(Sender: TObject);
    procedure btnCancelClick(Sender: TObject);
    procedure btnClearMemoryClick(Sender: TObject);
    procedure btnChangeClick(Sender: TObject);


  private
  rladd: real;
  rlvatinc: real;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}


procedure TForm1.btnCostClick(Sender: TObject);
 var
  errorQty,errorPrice,intQty : Integer;
  rlExVat,rlVat,rlPrice : Real;
  strVatInc,strExVat,strVat: string;

 begin
  val (edtQty.text, intQty, errorQty);
  if edtQty.text ='' then
 begin
  showmessage('Please enter the Quantity');
  exit;
 end;

  if errorQty <> 0 then
 begin
  showmessage('Please Enter the Correct Quantity');
  exit;
 end;
  val (edtPrice.text, rlPrice, errorPrice);
  if edtPrice.text ='' then
 begin
  showmessage('Please enter the price');
  exit;
 end;

 if errorPrice <> 0  then
 begin
  showmessage('Please type in the Correct Price');
  exit;
 end;

  rlExVat := intQty * rlPrice;
  rlVat := rlExVat * 0.175;
  rlVatInc := rlExVat + rlVat;

  str(rlExVat:0:2, strExVat);
  edtExVat.text := strExVat;

  str(rlVat:0:2,strVat);
  edtVat.text:= strVat;

  str(rlVatInc:0:2,strVatInc);
  edtVatInc.text:= strVatInc;
 end;
procedure TForm1.FormCreate(Sender: TObject);

 begin
  rlAdd := 0.0;
  btnSubTotal.Enabled := True;
  btnSubTotal.Enabled := False;
 end;

procedure TForm1.btnAddClick(Sender: TObject);
 var
  rlVatInc: Real;
  error: integer;
 begin
  val(edtVatInc.Text, rlVatInc, error);
  rlAdd := rlAdd + rlVatInc;
  btnSubTotal.Enabled := true;
 end;

procedure TForm1.btnSubTotalClick(Sender: TObject);
 var
  strVatInc: string;
 begin
  str(rlAdd:0:2, strVatInc);
  edtVatInc.Text := strVatInc;
 end;

procedure TForm1.btnClearClick(Sender: TObject);
 begin
  edtExVat.clear;
  edtVat.clear;
  edtPrice.clear;
  edtQty.clear;
  edtVatInc.text := '0.0';
 end;

procedure TForm1.btnCancelClick(Sender: TObject);
 var
  rlVatInc: real;
  error: integer;
 begin
  val(edtVatInc.Text, rlVatInc, error);
  rlAdd := rlAdd - rlVatInc;
  btnSubTotal.Enabled := true;
 end;

procedure TForm1.btnClearMemoryClick(Sender: TObject);
 begin
  rlAdd := 0.0;
 end;

procedure TForm1.btnChangeClick(Sender: TObject);
 var
  rlChange,rlCash: Real;
  errorCash: Integer;
  strChange: String;
 begin
  val (edtCash.text, rlCash, errorCash);
  if edtCash.text ='' then
 begin
  showmessage('Please enter the Quantity');
  exit;
 end;

 if errorcash <> 0 then
 begin
  showmessage('Please Enter the Correct Quantity');
  exit;
 end;
  rlChange:= rlCash - rlVatInc ;
  str(rlChange:0:2,strChange);
  edtChange.text:= strChange;
end;
end.