Dear All,
I have two units, Unit1 and Unit2 , i would like to access a boolean from Unit1 to Unit2 , i have tried it in the following way, but i have got the error "Zugriffsverletzung bei Adresse 023C4B58 in Modul 'Test.exe'. Lesen von Adresse 0000"

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Code:

//Unit1
Unit Unit1
type TCalculation = class(TForm)
  private
  protected
   FNewvalue: Boolean;
  public
   property Newvalue: Boolean read FNewvalue;
   
  end;

//Unit2
Unit Unit2
type Taccounts = class(TForm)

 interface

uses
  Unit1
   
  private
  protected
  public
    procedure Checkvalue(Sender: TObject);
  end;

implementation

procedure Taccounts .Checkvalue(Sender: TObject);
var
  f : TCalculation ; // i have created an instance of TCalculation    
begin
if f.Newvalue = True then // i have called the boolean
//check the condition
End;

could you please tell me ,how can i make it works?

Zitat von question:

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Code:

...procedure Taccounts .Checkvalue(Sender: TObject);
var
  f : TCalculation ; // i have created an instance of TCalculation    
begin
if f.Newvalue = True then // i have called the boolean
End;

... but you are not accessing the instance your have created. Instead, you access 'f', which is undefined at this point.

Where is your created instance of 'TCalculation'?

Could you please tell me ,how can i create the instance of 'TCalculation'? i am reading some tutorial,but i am not so clear, could you please give me an example ?

Zitat von question:

Could you please tell me ,how can i create the instance of 'TCalculation'? i am reading some tutorial,but i am not so clear, could you please give me an example ?

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Delphi-Quellcode:

var
  f: TCalculation; // declaration
begin
  f := TCalculation.Create; // create instance
  ...

Hi , i got the error " Nicht genünged wirklich parameter"

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Code:

var
  f: TCalculation;
begin
  f := TCalculation.Create; // Here pointing the error("Nicht genünged wirklich parameter")
  ...

TCalculation is of kind TForm, whose constructor expects an Owner-parameter. If you don' t want to set an owner, simply pass nil.
f := TCalculation.Create(nil); I think you should read some basics-tutorial, e.g. here.

Thanks for the link, i am following this tutorial,but i have another question, i have done the progem, now there is no error,but i am not getting the expected value of Modified(its a Boolean var)

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Code:

var
  f: TCalculation;
begin
  f := TCalculation.Create(nil);
  if f.FNewvalue = True then // the FNewvalue is always zero, which is unexpected
  //this will hapen
  else
    //this
end;

This is not unexpected, you create a new instance, therefore its properties are set to default unless something happens which changes them.

[edit] BTW: You should never compare to true or false, this can lead to unexpected results.
if var = true then -->
if var then [/edit]

Is it also possible to create a class exactly as it is(not as a new instance), i mean i want to create a class of TCalculation so that i can access any of its variable with the exact value from class of TAccounts

i even dont know whether its possible or not, i was looking in tutorial but dont get any idea yet, can you please help me ?

You have 2 different classes derived from TPersistent with similar properties? In that case you can override the "Assign" or even better the "AssignTo"-Method. This should do exactly what you want. There should be examples for both methods in this forum: Assign, AssignTo.