A Simple Math evaluator
lazarus / 8-Other

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BenJones · 2011-08-12 09:01

Hi this is my simple math evaluator I been working on since last week.
it only basic at the moment can do things like 2 + 2 * 3 does not
support brackets yet but am working on it. hope to include it soon in
my little scripting lanuage project I want to make.

Comments welcome. Hope you find it of some use.
How to use start a new project and add this code.

Code: [Select]unit Unit1;

{$mode objfpc}{$H+}

interface

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

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

function isOp(aSign: string): boolean;
begin
  Result := False;
  if aSign = '+' then
    Result := True;
  if aSign = '-' then
    Result := True;
  if aSign = '*' then
    Result := True;
  if aSign = '/' then
    Result := True;
end;

function GetToken(expression: string; out Counter: integer): variant;
var
  aChar: string;
  sData: string;
begin

  repeat
    //Get Char
    aChar := expression[Counter];

    //Skip white space
    if aChar = ' ' then
      aChar := '';
    //Check if operator
    if isOp(aChar) then
    begin
      //Exit from loop
      break;
    end
    else
    begin
      //Build String
      sData := sData + aChar;
      //Inc Counter
      Inc(Counter);
    end;
  until Counter > Length(expression);
  //Return result
  Result := StrToInt(sData);
end;

function Eval(expression: string): variant;
var
  aChar: string;
  aOperator: string;
  Ret: variant;
  iCount: integer;
begin
  iCount := 1;

  while iCount < Length(expression) do
  begin
    //Get char
    aChar := expression[iCount];

    if isOp(aChar) then
    begin
      //Get operator
      aOperator := Copy(expression, iCount, 1);
      //INC Counter
      Inc(iCount);
    end;

    //Check for operators
    if aOperator = '' then
    begin
      Ret := Trim(GetToken(expression, iCount));
    end;
    //Do Add
    if aOperator = '+' then
    begin
      Ret := Ret + GetToken(expression, iCount);
    end;
    //Add Subtract
    if aOperator = '-' then
    begin
      Ret := Ret - GetToken(expression, iCount);
    end;
    //Do Times
    if aOperator = '*' then
    begin
      Ret := Ret * GetToken(expression, iCount);
    end;
    //Do Divide
    if aOperator = '/' then
    begin
      Ret := Ret / GetToken(expression, iCount);
    end;
  end;
  //Return result
  Result := Ret;
end;

Add a command button then add this code.

Code: [Select]self.Text := Eval('5 + 5 + 5 + 5 * 2 - 1 / 2'); //
Returns 19.5

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marcov · 2011-08-12 10:46

Have a look at unit symbolic :-)

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Leledumbo · 2011-08-12 14:07

QuoteHave a look at unit symbolic :-)The unit is good, but it misses
documentation...

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marcov · 2011-08-12 17:07

Quote from: Leledumbo on August 12, 2011, 04:07:42 pmQuoteHave a look
at unit symbolic :-)The unit is good, but it misses documentation...

There are examples.

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Leledumbo · 2011-08-12 22:11

Yes, that's where I learned how to use it besides the unit source
code.

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marcov · 2011-08-14 13:55

Quote from: Leledumbo on August 13, 2011, 12:11:23 amYes, that's where
I learned how to use it besides the unit source code.

I added a routine that simplifies basic usage to trunk (2.7.1)

Basically you can do

 quickevaluate('5+(5-2)*(10+43)',[],[])

and it will return an extended value or throw an exception on error.
Variables are also possible.

An example for the new functionality was added called easyevalexample