I copy this code from Martin Austermeier, hope this code help you
Calc.pas
unit Calc;
(***********************************************************************
simple calculator for Delphi programs
by Martin Austermeier CIS 100116,3455
Version 1.1 - 10.10.95:
* corrected embarassing subtract bug
* "overflow" error display
* deleted some unnecessary code
--------------------------------------------------------------
This is not a component; just include it with "USES Calc".
Sorry, I don't have the time to write mucho documentation.
Only a few items:
* you might want to change the Form's Caption.
* the calculator is designed to show results with two decimal places.
Look at SetResult (PRECISION, DECIMAL_PLACES) if you want to change this.
* there are only the basic functions.
Not even a "percent" button.. ;-)
If you integrate new buttons, you should set their "Tag" property,
and process them like in CalcButtonClick()
* I invoke the calculator as a modal form (see ShowCalculator).
You'd have to write a Close mechanism if you want to use it as
a non-modal window.
* a typical call would look like
var myNumber : Double;
begin
myNumber := 123.45;
if Calc.Showcalculator(myNumber) then [myNumber has changed];
end;
**********************************************************************)
interface
uses
SysUtils, WinTypes, WinProcs, Messages, Classes,
Forms, Buttons, Controls, StdCtrls, ExtCtrls;
type
TCalcStatus = (CS_FIRST, CS_VALID, { the rest is error stati }
CS_ERROR, CS_OVERFLOW);
type
TCalculator = class(TForm)
MainPanel: TPanel;
DisplayPanel: TPanel;
BottomPanel: TPanel;
Panel3: TPanel;
resultLabel: TLabel;
Button1: TButton;
Button2: TButton;
Button3: TButton;
Button4: TButton;
Button5: TButton;
Button6: TButton;
Button7: TButton;
Button8: TButton;
Button9: TButton;
Button0: TButton;
ButtonComma: TButton;
ButtonDiv: TButton;
ButtonMult: TButton;
ButtonSub: TButton;
ButtonAdd: TButton;
ButtonSign: TButton;
ButtonC: TButton;
ButtonEq: TButton;
okBtn: TBitBtn;
cancelBtn: TBitBtn;
procedure CalcButtonClick(Sender: TObject);
procedure OkBtnClick(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure FormKeyPress(Sender: TObject; var Key: Char);
private
{ Private-Declaration }
fResult : Double;
fDisplayText : String[30];
fStatus : TCalcStatus;
operand : Double;
operator : Char;
procedure SetResult(r : Double);
function GetResult : Double;
procedure SetStatus(stat : TCalcStatus);
procedure SetDisplayText(s : String);
function GetDisplayText : String;
property Status : TCalcStatus read fStatus write SetStatus;
property DisplayText : String read GetDisplayText write SetDisplayText;
public
{ Public-Declaration }
property CalcResult : Double read GetResult write SetResult;
procedure Clear;
end;
var
Calculator: TCalculator;
function ShowCalculator(var number : Double) : Boolean;
{ display modal (inital result=number); return "number", if TRUE }
implementation
{$R *.DFM}
function ShowCalculator(var number : Double) : Boolean;
begin
Calculator := TCalculator.Create(application);
try
Calculator.CalcResult := number;
if (Calculator.ShowModal = MROK) then
number := Calculator.CalcResult;
finally
Calculator.Free;
end;
end;
procedure TCalculator.SetResult(r : Double);
const
PRECISION = 15;
DECIMAL_PLACES = 2;
begin
fResult := r;
DisplayText := FloatToStrF(fResult, ffFixed, PRECISION, DECIMAL_PLACES);
end;
function TCalculator.GetResult : Double;
begin
result := StrToFloat(DisplayText);
end;
procedure TCalculator.SetStatus(stat : TCalcStatus);
begin
fStatus := stat;
if (fStatus >= CS_ERROR) then
MessageBeep(MB_ICONSTOP);
end;
procedure TCalculator.SetDisplayText(s : String);
const
MAX_LEN = 17; { max# digits in display }
begin
if (Length(s) <= MAX_LEN) then
resultLabel.Caption := s
else begin
Status := CS_OVERFLOW;
end;
end;
function TCalculator.GetDisplayText : String;
begin
result := resultLabel.Caption;
end;
procedure TCalculator.FormCreate(Sender: TObject);
begin
Clear;
end;
procedure TCalculator.Clear;
begin
Status := CS_FIRST;
DisplayText := '0';
operand := 0;
operator := #0;
end;
procedure TCalculator.CalcButtonClick(Sender: TObject);
var
k : Char;
begin
if (Sender is TButton) then begin
ButtonEq.SetFocus; { default button }
k := Char(TButton(Sender).Tag);
FormKeyPress(Sender, k);
end;
end;
procedure TCalculator.OkBtnClick(Sender: TObject);
var
k : Char;
begin
k := '=';
FormKeyPress(self, k); { simulate "=" to get result }
end;
procedure TCalculator.FormKeyPress(Sender: TObject; var Key: Char);
const
KEY_SIGN = '#';
KEY_CLEAR = 'C';
KEY_DECIMAL = '.';
ERR_TXT = 'Error';
OFL_TXT = 'Overflow';
var
k : Char;
begin
k := UpCase(key);
if (k = decimalSeparator) then
k := KEY_DECIMAL;
if (Status <>
or (k = KEY_CLEAR) then
case k of
'0'..'9': begin
if (Status = CS_FIRST) or (DisplayText = '0') then
DisplayText := '';
Status := CS_VALID;
DisplayText := DisplayText + k;
end;
#8 : begin
if (Length(DisplayText) > 0) then begin
DisplayText := Copy(DisplayText, 1, Length(DisplayText)-1);
if (Length(DisplayText) = 0) then
DisplayText := '0';
Status := CS_VALID;
end;
end;
KEY_DECIMAL: begin
if (Pos(decimalSeparator, DisplayText) = 0) then
DisplayText := DisplayText + decimalSeparator;
Status := CS_VALID;
end;
'+', '-', '/', '*', '=' : begin
case operator of
'+': begin
CalcResult := operand + CalcResult;
end;
'-': begin
CalcResult := operand - CalcResult;
end;
'*': begin
CalcResult := operand * CalcResult;
end;
'/': begin
if (CalcResult = 0) then
Status := CS_ERROR
else
CalcResult := operand / CalcResult;
end;
end;
if (Status <> CS_ERROR) then begin
Status := CS_FIRST;
operand := CalcResult;
operator := k;
end;
end;
KEY_SIGN: begin
CalcResult := -CalcResult;
end;
KEY_CLEAR: begin
Clear;
end;
end;
case Status of { in case of error.. }
CS_ERROR : DisplayText := ERR_TXT;
CS_OVERFLOW : DisplayText := OFL_TXT;
end;
end;
end.
Program Project1
program Project1;
uses
Forms;
{$R *.res}
begin
Application.Initialize;
Application.Run;
end.
And the result is :
