Eleicao Presidencial While - PASCAL

Program Pzim ;
var
 nul,branco,lula,dilma,serra,plinio: integer;
 opcao,cont: integer;
 res: boolean;
 Begin
  res:= true;
  nul:=0;
    While res do {pode ser tbm while (res=true) do}
    Begin
     cont:= cont + 1;
     WriteLn('1 ----- Lula');
     WriteLn('2 ----- Dilma');
     WriteLn('3 ----- Serra');
     WriteLn('4 ----- Plinio');
     WriteLn('5 ------------ Nulo');
     WriteLn('6 ------------ Branco');
     WriteLn('0 ------------ Sair');
     Write('Opcao: ');
     readln(opcao);
      if (opcao = 1) then
       lula:= lula + 1
      else if (opcao = 2) then
       dilma:= dilma + 1
      else if (opcao = 3) then
       serra:= serra + 1
      else if (opcao = 4) then
       plinio:= plinio + 1
      else if (opcao = 5) then
       nul:=nul+1
      else if (opcao = 6) then
       branco:=branco + 1
      else if (opcao = 0) then
       Begin
        res:= false;
        cont := cont - 1;
       end;
     clrscr;
    end;
    Writeln('Lula   ',lula,' ',lula/cont*100:3:0,'%');
    Writeln('Dilma  ',dilma,' ',dilma/cont*100:3:0,'%');
    Writeln('Serra  ',serra,' ',serra/cont*100:3:0,'%');
    Writeln('Plinio ',plinio,' ',plinio/cont*100:3:0,'%');
    Writeln('   Nulo   ',nul,' ',nul/cont*100:3:0,'%');
    Writeln('   Branco ',branco,' ',branco/cont*100:3:0,'%');
    Writeln('               by Marcus Vinicius');
 End.