dluedi
asked on
EInvalidOp
Hello I get that stupid error if I do this
{---}
function error:extended;
begin
error:=1/2;
end;
procedure TForm1.Button1Click(Sender
var
xw:extended;
begin
xw:=error+xw; // if you write xw:=1/2+xw there is no compiler error!
end;
end.
{---}
You sure now why!
:)dluedi
{---}
function error:extended;
begin
error:=1/2;
end;
procedure TForm1.Button1Click(Sender
var
xw:extended;
begin
xw:=error+xw; // if you write xw:=1/2+xw there is no compiler error!
end;
end.
{---}
You sure now why!
:)dluedi
ASKER
Sorry, I made a mistake, of course EInvalidOp is no compiler error, and the error I am talking about happens when program is running...this program looks quite wired, that's because I shortend it (in reality it sure doesn't look like this). I just wanted to make it simple...I think I need just to define xw in oncreate...I'll try it. I thaught that if a variable is not yet defined its 0
But isn't it still strange that xw:=1/2+xw doesn't create an EInvalidOp but xw:=error+xw does....its actually the same????
But isn't it still strange that xw:=1/2+xw doesn't create an EInvalidOp but xw:=error+xw does....its actually the same????
just a guess
try this change
function error:extended;
begin
Result:=1/2;
end;
just to say that error is a constant in the windows unit,
maybe this causes the problem
meikl ;-)
try this change
function error:extended;
begin
Result:=1/2;
end;
just to say that error is a constant in the windows unit,
maybe this causes the problem
meikl ;-)
xw := error + xw
xw-xw := error
0 <> 1/2 thus it is an invalid statement
You need to initialize error as a constant and xw needs a value assigned to it in order for the calculation to work.
Thas is basically what the other experts are saying.
xw-xw := error
0 <> 1/2 thus it is an invalid statement
You need to initialize error as a constant and xw needs a value assigned to it in order for the calculation to work.
Thas is basically what the other experts are saying.
Well, it's no mathematical formula here, it's an "assignment". I mean, in pascal we write ":=", we don't write "=" and that has a meaning! The purpose is to show that both sides may not be equal before the assignment. You can also do this:
var xw : integer;
begin
xw := 5;
xw := 10 + xw;
You could also say here xw-xw := 10 and 0 <> 10. But that doesn't matter, because it's an *assignment*.
Regards, Madshi.
var xw : integer;
begin
xw := 5;
xw := 10 + xw;
You could also say here xw-xw := 10 and 0 <> 10. But that doesn't matter, because it's an *assignment*.
Regards, Madshi.
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Your'e right Madshi! I realized the error after I posted.
But I do appreciate your excellent observation and discussion on the difference between '=' and ':='.
I realized my mistake when I thought about incrementing a number:
i := i+1;
anyway, you are correct the value must be initialized.
But I do appreciate your excellent observation and discussion on the difference between '=' and ':='.
I realized my mistake when I thought about incrementing a number:
i := i+1;
anyway, you are correct the value must be initialized.
:-)
Furthermore your code doesn't make much sense. I mean in this line:
xw:=error+xw; // if you write xw:=1/2+xw there is no
The "xw" variable is undefined. So it's like using:
xw:=error+aWildValueNobody
What's the sense of it?
Regards, Madshi.