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Problem with int() and trunc() !

Posted on 1998-05-20
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Last Modified: 2010-04-06
Math problem !!!!!!!!

normally int(226.0) returns 226 and
trunc(226.0) returns 226

But I am getting both returning 225
in the code below !


   function EvenCmClasses(OriginalHt:Double) : Double;
   {Converts X to an even cm class, and rounds to two       decimals}
   var
      Ht100, Ht1000, InitialClass : Double;
      CorrectIt : LongInt;
   begin
      Ht100:= OriginalHt*100.0;
      Ht1000:= OriginalHt*1000.0;
      CorrectIt:= Trunc(Ht100);
      InitialClass:= CorrectIt/100.0;
     {InitialClass:= Int(Ht100)/100.0;}

The OriginalHt comes from a sum of a
TOvcPictureArrayEditor set to datatype = ptfDouble

Watches shows OriginalHt = 226

Can anyone give me some help with this ?

John.
0
Comment
Question by:jturpin
7 Comments
 
LVL 2

Expert Comment

by:kjteng
ID: 1346724
i run your code and find the OriginalHt=226 and initialClass=226.
How did you get 225?
what is ptfDouble? a pointer type?
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LVL 5

Expert Comment

by:JimBob091197
ID: 1346725
I agree with kjteng.

Are you trying to round to 2 decimal places?  If so, then your logic is currently "(Int(Num * 100)) / 100".  However, this will always round down, e.g. 226.236 becomes 226.23.  To fix this, add 0.5 after the Int part, i.e. "(Int((Num * 100) + 0.5)) / 100".

Then 226.234 -> 226.23, but 226.235 -> 226.24

In your particular example, I get 226 like kjteng.

Regards,
JB
0
 
LVL 1

Author Comment

by:jturpin
ID: 1346726
I have no idea why it is returning 225. I
was hoping someone could give me some
pointers.

ptfDouble is one of the enumerated values
used by Orpheus. It defines the field data
type as double.

Did you both use orpheus ?

In this routine I need to cut the number off
after the second decimal, without rounding.

John.
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LVL 5

Expert Comment

by:JimBob091197
ID: 1346727
Hi again,

I don't use Orpheus, although that shouldn't matter.

This is a very strange problem you have.  If you like, you can e-mail me a sample app which gives the incorrect value, and I can have a look at it.  My e-mail address is davekw@iafrica.com.

Regards,
JB
0
 
LVL 2

Expert Comment

by:kjteng
ID: 1346728
The problem MAT BE due to the actual parameter passed to the function. Check the variable type and also watch the value of the number before it is passed to the function. I suspect that the value passed to the function was 225.99999999 and the .999999 was trucated.

I do not use orpheus though i heard of that before.
0
 
LVL 2

Expert Comment

by:kjteng
ID: 1346729
The problem MAY BE due to the actual parameter passed to the function. Check the variable type and also watch the value of the number before it is passed to the function. I suspect that the value passed to the function was 225.99999999 and the .999999 was trucated.

I do not use orpheus though i heard of that before.
0
 
LVL 3

Accepted Solution

by:
rickpet earned 200 total points
ID: 1346730
As stated earlier by kjteng...you are most likely passing 225.999999999, Delphi's IDE show's this as 226 and not 225.999999999, even though it stores it and handles it as 225.999999999. Step through the code and watch the variables...you'll see what I mean.

Rick

function MyTrunc(value: Double): double;
begin
  value := value * 100.0;
  value := trunc(value);
  result := value/100.0;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  myDouble: double;
begin
  myDouble := 225.999999999;
  Label1.Caption := FloatToStr(MyTrunc(myDouble));
end;

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