求用delpi编写计算器！！谢谢了！！

unit untJCalc;

interface

uses
classes,sysutils;

type
TJStack=class
private
Lines:TStrings;
public
constructor Create;
destructor Destroy;
procedure init;
procedure push(s:string);
function GetTop:String;
function Pop:String;
end;
TJExpr=class
private
Expr:String;
Position:Integer;
Min,max:Integer;
Eof:Boolean;
public
constructor Create(pExpr:String);
function read:String;
procedure GoFirst;
end;

function CalcExpr(sExpr:String):String;
function CalcExprItem(sOptr,sA,sB:String):String;
function OptrIndex(w:string):Integer;
function GetParamCount(pFunc:String):Integer;
function ExecFunc(pFunc:String;pParam:Array of string;pParamCount:Integer