how to call a Dll and pass parameters to it in delphi 7

I am a delphi noob so please help me out with this. I have created a DLL with the following code:

 library PRdll;
   uses
 ExceptionLog, SysUtils,Classes,Dialogs;

{$R *.res}

  function DllMessage(var a:integer):Integer;stdcall;export;
  begin
      Showmessage('GHelloa');//this is displayed
      ShowMessage(IntToStr(a));//I get the error at this point
       Result:=5;
  end;

    exports DllMessage;
  begin
  end.

The corresponding call to the DLL is given by this code:

    var
      FDll: TFDll;
       function DllMessage(var a:integer):integer;stdcall;external 'PRDll.dll';
     implementation

    {$R *.dfm}

       procedure TFDll.btnCallDllClick(Sender: TObject);
      var
       i:integer;
      s1:string;
      begin
           i:=5;
          s1:=IntToStr(DllMessage(i));
         //ShowMessage(s1);
         end;

I get an access error. Why does this happen . ANybody ? he开发者_如何学Golp!!! Thanks in Advance

Have you added sharemem unit?
See the help.

Second option: Comment the ExceptionLog line and try again.
It work fine.

Regards.

The correct code is posted below; i am surprised why no one could tell me this simple thing

//Dll
 library ProDll;

uses
   ExceptionLog,
  SysUtils,
  Classes,Dialogs;

  function showSqRoot(var a:Double):Double; stdcall; export;
  begin

     Result:=sqrt(a);
   end;

   exports showSqRoot;
  {$R *.res}

   begin
    end.


 //The program
   function showSqRoot(var a:Double):Double;stdcall external 'ProDll.dll'//Notice 'stdcall external' here

 procedure TFcallDLL.btnCallDLLClick(Sender: TObject);
  var
        numInput,numRes:Double;   {Input and Result}
   begin
       numInput:=StrToFloat(edtInput.Text);
      numRes:=showSqRoot(numInput);   {call the function in DLL with the Parameter}
      edtResult.Text:=FloatToStr(numRes); {Display the Result}
    end;

This code has worked fine for me.