unit LoginForm;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Imaging.pngimage,
  Vcl.ExtCtrls, Data.DB, Data.Win.ADODB;

type
  TfrmLoginForm = class(TForm)
    lblUsername: TLabel;
    lblPassword: TLabel;
    edtUsername: TEdit;
    edtPassword: TEdit;
    btnLogin: TButton;
    imgLock: TImage;
    lblWelcome: TLabel;
    conUsers: TADOConnection;
    tblUsers: TADOTable;
    dsUsers: TDataSource;
    procedure btnLoginClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  frmLoginForm: TfrmLoginForm;

implementation

{$R *.dfm}

procedure TfrmLoginForm.btnLoginClick(Sender: TObject);
  var
    sUsername, sPassword : string;
    bUsername, bPassword : Boolean;
begin
  sUsername := edtUsername.Text;
  sPassword := edtPassword.Text;
  bUsername := False;
  bPassword := False;

  tblUsers.First;
  while not tblUsers.Eof do
    begin
      if (sUsername = tblUsers.FieldByName('Username').AsString) and
         (sPassword = tblUsers.FieldByName('Password').AsString) then
        begin
          bUsername := True;
          bPassword := True;
        end;

      if (sUsername = tblUsers.FieldByName('Username').AsString) and
         (sPassword <> tblUsers.FieldByName('Password').AsString) then
        begin
          bUsername := True;
          bPassword := False;
        end;

      if (sUsername <> tblUsers.FieldByName('Username').AsString) and
         (sPassword = tblUsers.FieldByName('Password').AsString) then
        begin
          bUsername := False;
          bPassword := True;
        end;

      if (sUsername <> tblUsers.FieldByName('Username').AsString) and
         (sPassword <> tblUsers.FieldByName('Password').AsString) then
        begin
          bUsername := False;
          bPassword := False;
        end;

      if (bUsername and bPassword) then
        begin
          ShowMessage('Loged in as ' + sUsername);
        end;

      if (bUsername and (not bPassword)) then
        begin
          ShowMessage('Passowrd incorrect');
        end;

      if ((not bUsername) and bPassword) then
        begin
          ShowMessage(sUsername + ' does not exist');
        end;

      if ((not bUsername) and (not bPassword)) then
        begin
          ShowMessage(sUsername + ' does not exist');
        end;

      tblUsers.Next;
    end;
end;

end.