Delphi Tutorial # 5

Program Structure

A program is composed of three elements :

- Program Title

- Uses Clauses

- Declarations and Statements

Program title is the name of the program. Uses clauses include units that are used in the program. Declarations and statements are codes that will be executed by computer.

You can see an example of Delphi program structure in Delphi Tutorial # 2. See the codes project1.dpr file  below :

    program Project1;

    uses

      Forms,

      Unit1 in 'Unit1.pas' {MyForm};

    {$R *.RES}

    begin

      Application.Initialize;

      Application.CreateForm(TMyForm, MyForm);

      Application.Run;

    end.

The example above does not have declarations. Declaration is where we define constants, types, variables, procedures and functions. The structure of declarations is shown below :

     Const

           {constants list}

     Type

          {types create by user}

     Var

          {variables list}

          {functions and procedures}

Function is a routine that can be called by the program and will return a value. Procedure is a routine that does not return a value.

A program is usually formed by some source code modules that called units. A unit consist some routine (functions and procedures). It is saved as a unit file (.PAS). The structure of a unit is shown below :

       Unit unitname;

       Interface 

       Uses {units}

       {interface}

       Implementation

       Uses {units}

      {implementation}

       Initialization

       {Initialization}

       Finalization

       {Finalization}

       End.

The example of a unit is unit1.pas file :

    unit Unit1;

    interface

    uses

      Windows, Messages, SysUtils, Classes, Graphics, Controls,           Forms, Dialogs, StdCtrls;

    type

      TMyForm = class(TForm)

        Label1: TLabel;

        ExitButton: TButton;

        procedure ExitButtonClick(Sender: TObject);

      private

        { Private declarations }

      public

        { Public declarations }

      end;

    var

      MyForm: TMyForm;

    implementation

    {$R *.DFM}

    procedure TMyForm.ExitButtonClick(Sender: TObject);

    begin

     Application.Terminate;

    end;

    end.

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