result in simple code when variables are uninitialized

Question

Today one of my friend ask me about below code :

var
  a: Integer;
begin
  ShowMessage(IntToStr(a));
end;

This is local variable and not been initialized , ok ?

Put code in OnClick event of a button component and then run code in three diffrent ways below :

1. Click on the button and see result , result = 1635841
2. Press Enter key and see result , result = 1
3. Press Space key and see result , reuslt = 1636097

I test code in two diffrent computer & see same result , any idea about this ?

Answer 1

procedure TForm1.Button1Click(Sender: TObject);
var
  a: Integer;
begin
    ShowMessage(IntToStr(Integer(a)));
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
 ShowMessage(IntToStr(Integer(Pointer(TButtonControl(Button1)))));
end;

on my machine this code produces same message as compiler uses ebx register for a variable, while TButtonControl.WndProc uses ebx to store pointer to Self(as EAX will be overwritten after WinAPI function calls from TbuttonControl.WndProc) which is button1 before calling the actual handler Button1Click. So alas, on Delphi 2007 message text is too predictable.

[edited] You can see what's happening inside VCL while debugging if you turn on Use debug DCUs option in your project compiler options Compiler->Debugging->Use debug DCUs.

Answer 2

Since the variable is not initialized, its value can be anything. Since your result is 'something', there is nothing unusual at all going on here.