if then else loop problem delphi

I'm still a beginner and I have been trying to solve this problem by my self but I guess I 'm out of luck. I think it is probably quite simple but here's the deal.

I have 3 checkboxes. Each one writes a specific line in a text file when a button is pressed but if none are selected. I want a message to be displayed. But what happens there is that the message pops out even if one checkbox is checked. Here's the code: (btw, feel free to suggest any other code that would make it easier/clearer)

if cbSCV.Checked then
  WriteLn(permFile, '开发者_StackOverflow中文版scv');
if cbMP.Checked then
  WriteLn(permFile, 'mp');
if cbBTK.Checked then 
  WriteLn(permFile, 'btk'); 
if not (cbBTK.Checked) and not (cbMP.Checked) and not (cbBTK.Checked) then
  showmessage('Choose at least 1 option.');

try replacing the if sentence to

if not (cbBTK.Checked) and not (cbMP.Checked) and not (cbSCV.Checked) then

because you are checking the cbBTK.checked value twice

For what it's worth I'd probably reverse the logic and write the troublesome test like this:

if not (cbBTK.Checked or cbMP.Checked or cbSCV.Checked) then

To complement @soid's answer: I'd probably write it like this:

procedure TForm1.CheckIt;
var
  Count: Integer;

  procedure HandleCheckBox(ACheckBox: TCheckBox; const AID: string);
  begin
    if ACheckBox.Checked then
    begin
      WriteLn(permFile, AID);
      Inc(Count);
    end;
  end;

begin
  Count := 0;
  HandleCheckBox(cbSCV, 'scv');
  HandleCheckBox(cbMP, 'mp');
  HandleCheckBox(cbBTK, 'btk');
  if Count = 0 then
    ShowMessage('Choose at least 1 option.');
end;

This is a few more lines but it is IMHO less error prone and more "automatic" if you later need a fourth or fifth checkbox.

I would rewrite it like this:

if cbSCV.Checked then WriteLn(permFile, 'scv');
if cbMP .Checked then WriteLn(permFile, 'mp' );
if cbBTK.Checked then WriteLn(permFile, 'btk');

if not (cbSCV.Checked) and 
   not (cbMP .Checked) and 
   not (cbBTK.Checked)     then
  showmessage('Choose at least 1 option.');

This takes the same number of lines but places the repeated elements together to make it easy to read the whole construct quickly and spot places where you are not following the pattern. Your bug, which we have all had in our code, is easier to see if it is written like this.

Hmmm. For those things I like a set-based approach. One way is this

type
  TEnumSomething = (esSCV, esMP, esBTK);
  TSomethingSet = set of TEnumSomething;

{var section}
var
  Conj: TSomethingSet;
{code section}
Conj := [];
if cbSCV.checked then 
begin
  Conj := conj + [esSCV];
  WriteLn(permFile, 'scv');
end;  
{do this for the other 2 checkboxes}
If Conj = []  then ShowMessage('');

You can also make Conj an form field and make checkboxes set/unset this on their OnClick event.

Warning: maybe some syntax detail is missing, I'm not on delphi IDE now...

I probably wouldn't rewrite it like this, but hey, this is fun. I'm at work and I don't have Delphi here, so this is just sample code. Generics!

type
    TCheckBoxDict: TDictionary<String, TCheckBox>;
var
    Dict: TCheckBoxDict;
    function HandleCheckBoxes(ADict: TCheckBoxDict) : boolean;
    var
        Key: String;
        CheckBox: TCheckBox;
    begin
        Result := false;
        for Key in ADict.Keys do
            if ADict.Items[Key].Checked then
            begin
                WriteLn(permFile, Key);
                Result := true;
            end;
    end;
begin
    Dict := TCheckBoxDict.Create;
    Dict.Add('scv', cbSCV);
    Dict.Add('mp', cbMP);
    Dict.Add('btk', cbBTK);
    if not HandleCheckBoxes(Dict) then
        ShowMessage('Choose at least one option');
    Dict.Destroy;
end;