Delphi 7: How to use a combination of check boxes - delphi

Question

Am working an a small app in Delphi7 but am puzzles on how to use a combination of 3 check boxes
Example: if check.box1 and checkbox2 checked run system application with these prefs
or if checkbox1 only checked run system application with these prefs or if checkbox2 only checked run with these prefs

Answer 1

It sounds like you're having trouble getting started writing what you need, which is basically a series of if..then..else flow-control statements based on compound boolean expressions. You probably want a structure like the one below. I'm not going to show you the entire thing, because it's best for you to work it out for yourself, but this should give you the idea:
if (CheckBox1.Checked) and (CheckBox2.Checked) and not (CheckBox3.Checked) then
begin
// do one thing
end
else
begin
if (CheckBox1.Checked) and not (CheckBox2.Checked) and not (CheckBox3.Checked) then
begin
// do another thing
end
else
// etc
end;
If you're familiar with enumerated types, you might do better to declare one and use that to derive the selected preferences and then act upon them. The point of doing that is twofold: to increase the clarity of your code (at the expense of your code being longer, of course); and to separate the logic for calculating which preference the user has selected from the code which acts upon it.
Something like
type
TRunPreference = (rpNone, rpOne, rpTwo, rpThree, rpFour,
rpFive, rpSix, rpSeven, rpEight);
// rpOne..rpEight are for the 8 permutations of three booleans
// and the rpNone is to provide for initialising the variable
// with something which isn't one of the desired values
var
RunPreference : TRunPreference;
procedure TForm1.Button1Click(Sender: TObject);
begin
RunPreference := rpNone;
if (CheckBox1.Checked) and (CheckBox2.Checked) and not (CheckBox3.Checked) then
begin
RunPreference := rpOne;
end
else
begin
if (CheckBox1.Checked) and not (CheckBox2.Checked) and not (CheckBox3.Checked) then
begin
RunPreference := rpTwo;
end
else
; //
end;
case RunPreference of
rpNone :
; // do nothing
rpOne :
begin
// Act on rpOne
end;
rpTwo :
begin
// Act on rpTwo
end;
// etc
end; { Case of RunPreference }
end;

Answer 2

Inspired by MartynA's solution, and because I prefer compact code, here's how I would do it:
// For the three (sets of?) preferences, define bit values, and
// a variable to hold the combination of the selected preferences:
const
PrefA=1; PrefB=2; PrefC=4;
var
prefs: byte;
procedure TForm12.Button2Click(Sender: TObject);
begin
// whether a preference should be active or not becomes a simple `OR` function
// based on each checkbox's state
prefs := 0;
if CheckBox1.Checked then prefs := prefs or PrefA;
if CheckBox2.Checked then prefs := prefs or PrefB;
if CheckBox3.Checked then prefs := prefs or PrefC;
// then use a `case` statement to run according the preference combination
// The values like `PrefA or PrefC` can be used instead of numeric values,
// since they can be resolved at compile time.
// Whether they improve readability or not is ... (disputable)
case prefs of
0:
ShowMessage('Running without preferences');
PrefA:
ShowMessage('Running with PrefA alone');
PrefB:
ShowMessage('Running with PrefB alone');
PrefA or PrefB:
ShowMessage('Running with PrefA and PrefB');
PrefC:
ShowMessage('Running with PrefC alone');
PrefA or PrefC:
ShowMessage('Running with PrefA and PrefC');
PrefB or PrefC:
ShowMessage('Running with PrefB and PrefC');
PrefA or PrefB or PrefC:
ShowMessage('Running with PrefA and PrefB and PrefC');
end;
end;
If you need to check in your code whether a preference is active or not, you can do it like:
if (prefs and PrefB) then
// do whatever requires PrefB to be selected