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Need help with a rounding problem

Posted on 2004-10-19
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Last Modified: 2010-04-05
I need some code (formula) that can return an integer value based on these rules:

1. No rounding

 value       returned value
  0.9            0
  1.1            1
  1.5            1
   .5             0

2. < 1 rounding

 value        returned value
   .9              0
   1.1            1
   1.5            2
    .5            0

3. < 0.5 rounding
 
  value        returned value
    .3               0
    .5               1
   1.5              2
    1.2             1

Obviously the value can be any decimal number so I need a formula or three that can handle this kind of rounding.

0
Comment
Question by:rutledgj
12 Comments
 
LVL 17

Accepted Solution

by:
geobul earned 100 total points
ID: 12348607
Hi,

1. Use Trunc function

2. What is the logic here?

3. Use:

function RoundUp(X: Extended): Int64;
begin
  Result := Trunc(X) + Trunc(Frac(X) * 2);
end;

Regards, Geo
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 12348668
1.
var
  I:      Integer;
  D:      Double;
begin
  D := 0.9;
  I := Round(Int(D));
  Edit1.Text := IntToStr(I);
end;

2.
var
  I:      Integer;
  D:      Double;
begin
  D := 0.9;
  I := Round(D);
  Edit1.Text := IntToStr(I);
end;
0
 
LVL 14

Expert Comment

by:DragonSlayer
ID: 12348788
Also check out the floor and ceil functions in the maths unit
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 12350702
procedure TForm1.Button1Click(Sender: TObject);
var
  I:      Integer;
  DA:     array[0..3] of Double;
begin
  DA[0] := 0.9;
  DA[1] := 1.1;
  DA[2] := 1.5;
  DA[3] := 0.5;
  for I := 0 to 3 do
    ListBox1.Items.Add(FloatToStr(Floor(DA[I])));
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  I:      Integer;
  DA:     array[0..3] of Double;
begin
  DA[0] := 0.9;
  DA[1] := 1.1;
  DA[2] := 1.5;
  DA[3] := 0.5;
  for I := 0 to 3 do
  begin
      if (DA[I]<1) then
        ListBox2.Items.Add(FloatToStr(Floor(DA[I])))
      else
        ListBox2.Items.Add(FloatToStr(Round(DA[I])));
  end;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
  I:      Integer;
  DA:     array[0..3] of Double;
begin
  DA[0] := 0.3;
  DA[1] := 0.5;
  DA[2] := 1.5;
  DA[3] := 1.2;
  for I := 0 to 3 do
  begin
      if (DA[I]<0.5) then
        ListBox3.Items.Add(FloatToStr(Floor(DA[I])))
      else
        ListBox3.Items.Add(FloatToStr(Round(DA[I]+0.00000001)));
  end;
end;
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 12350734
Post
Button1, Button2, Button3,
ListBox1, ListBox2, ListBox3
on the Form1 to see the results from above code.
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LVL 17

Expert Comment

by:geobul
ID: 12356985
I'm surprised :-(  

BTW in the accepted answer:
- The first one will behave unexpectedly with negative numbers, i.e. '-1.5' will become '-2' instead of '-1'.
- I can't say anythung about 2 because I haven't understood the requirement.
- IMHO the last one is wrong. That constant depends on the type of the real variable and its specific representation (OS, processor, etc.).
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 12362112
Hi Geo, you are right !
I did not think abot the negative values at all ....
Your solutions about [1.] and [3.] are elegant !

So, how we could solve I am graded in mistake ?
I think the page editor could redirect points to you.
0
 
LVL 12

Assisted Solution

by:esoftbg
esoftbg earned 50 total points
ID: 12362192
I provide here a correct version of the [2.] which works fine with both positive and negative values:

procedure TForm1.Button2Click(Sender: TObject);
type
  TSignIs = (siMinus, siPlus);
var
  I:      Integer;
  J:      Integer;
  DA:     array[0..7] of Double;
  SignIs: TSignIs;
begin
  DA[0] := -0.5;
  DA[1] := -1.5;
  DA[2] := -1.1;
  DA[3] := -0.9;
  DA[4] := 0.9;
  DA[5] := 1.1;
  DA[6] := 1.5;
  DA[7] := 0.5;
  for I := 0 to 7 do
  begin
    if (DA[I]>=0) then
      SignIs := siPlus
    else
    begin
      SignIs := siMinus;
      DA[I] := ABS(DA[I]);
    end;
    if (DA[I]<1) then
      J := Floor(DA[I])
    else
      J := Round(DA[I]);
    if (SignIs=siMinus) then
      J := - J;
    ListBox2.Items.Add(IntToStr(J));
  end;
end;
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 12367070
kretzschmar,
please redirect the points of this question to geobul,
because his solutions are correct and elegant.
Emil.
0
 
LVL 17

Expert Comment

by:geobul
ID: 12367204
Hi Emo,

The questioner is the one who decides which answer fits his needs. It is most likely that he doesn't care about negative numbers at all. So, there is no problem with the grading. I just wanted to leave my thougths for eventual future readers of this question. Hope it's clear now.

BTW. Congratulations, Emo, for your outstanding work here at Ex-Ex. I don't feel alone anymore ;-)
0
 

Author Comment

by:rutledgj
ID: 12368367
You are right. Negative numbers were not a concern.

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