Double is doing incorrect subtraction

I have the following code:

Dim x As Double = 45.333
Dim y As Double = 45
Dim z As Double = x - y
Me.Label1.Text = z.ToString()

The result should obviously be 0.333, but the value displayed in
Me.Label1.Text is:

0.332999999999998

I have seen stuff like this in other situations, but I never managed to
figure out how to fix it. Can somebody help me here?
--
Nathan Sokalski
njsokalski@hotmail.com
http://www.nathansokalski.com/

Re: Double is doing incorrect subtraction

"Nathan Sokalski" kirjoitti viestissä
news:uo2qJTVVIHA.5348@TK2MSFTNGP03.phx.gbl...
>I have the following code:
>
> Dim x As Double = 45.333
> Dim y As Double = 45
> Dim z As Double = x - y
> Me.Label1.Text = z.ToString()
>
> The result should obviously be 0.333, but the value displayed in
> Me.Label1.Text is:
>
> 0.332999999999998
>
> I have seen stuff like this in other situations, but I never managed to
> figure out how to fix it. Can somebody help me here?

In order to show the correct result you have to format it. For example you
could do this:
Me.Label1.Text =z.ToString("0.000")

Doubles are floating point numbers and that causes this behavior.

If you want to find more information try keyword "IEEE 754" with Google.

-Teemu

RE: Double is doing incorrect subtraction

Consider using decimal instead of double if you want to get the answer you
expect below.

"Nathan Sokalski" wrote:

> I have the following code:
>
> Dim x As Double = 45.333
> Dim y As Double = 45
> Dim z As Double = x - y
> Me.Label1.Text = z.ToString()
>
> The result should obviously be 0.333, but the value displayed in
> Me.Label1.Text is:
>
> 0.332999999999998
>
> I have seen stuff like this in other situations, but I never managed to
> figure out how to fix it. Can somebody help me here?
> --
> Nathan Sokalski
> njsokalski@hotmail.com
> http://www.nathansokalski.com/
>
>
>

Re: Double is doing incorrect subtraction

On Sat, 12 Jan 2008 14:53:22 -0500, Nathan Sokalski wrote:

> I have the following code:
>
> Dim x As Double = 45.333
> Dim y As Double = 45
> Dim z As Double = x - y
> Me.Label1.Text = z.ToString()
>
> The result should obviously be 0.333, but the value displayed in
> Me.Label1.Text is:
>
> 0.332999999999998
>
> I have seen stuff like this in other situations, but I never managed to
> figure out how to fix it. Can somebody help me here?

Double is doing entirely correct subtraction.

The problem is that Double is an implementation of IEEE floating point, and
IEEE floating point is incapable of representing all numbers exactly.

Read this:

http://support.microsoft.com/kb/42980

Re: Double is doing incorrect subtraction

Nathan,

This is basic

Float, Double or whatever floating poing calculation for mathimatical
programming,
Decimal for business programming,

Cor

Re: Double is doing incorrect subtraction

"Nathan Sokalski" schrieb:
> Dim x As Double = 45.333
> Dim y As Double = 45
> Dim z As Double = x - y
> Me.Label1.Text = z.ToString()
>
> The result should obviously be 0.333, but the value displayed in
> Me.Label1.Text is:
>
> 0.332999999999998
>
> I have seen stuff like this in other situations, but I never managed to
> figure out how to fix it. Can somebody help me here?

In addition to the other replies, take a look at these articles:

IEEE Standard 754 Floating Point Numbers


--
M S Herfried K. Wagner
M V P
V B

RE: Double is doing incorrect subtraction

perfections to show that she is the image of God, and
some defects to show that she is only His image.

581. God prefers rather to incline the will than the intellect. Perfect
clearness would be of use to the intellect and would harm the will. To
humble pride.

582. We make an idol of truth itself; for truth apart from charity is not
God, but His image and idol, which we must neither love nor worship; and
still less must we love or worship its opposite, namely, falsehood.

I can easily love total darkness; but if God keeps me in a state of
semi-darkness, such partial darkness displeases me, and, because I do not
see therein the advantage of total darkness, it is unpleasant to me. This is
a fault and a sign that I make for myself an idol of darkness, apart from
the order of God. Now only His order must be worshipped.

583. The feeble-minded are people who know the truth, but only affirm it so
far as consistent with their own interest. But, apart from that, they
renounce it.

584. The world exists for the exercise of mercy and judgement, not as if men
were placed in it out of the hands of God, but as hostile to

Re: Double is doing incorrect subtraction

hand; ye shall lie down in sorrow.

"Hearken to me, ye that follow after righteousness, ye that seek the Lord:
look unto the rock whence ye are hewn, and to the hole of the pit whence ye
are digged. Look unto Abraham, your father, and unto Sarah that bare you:
for I called him alone, when childless, and increased him. Behold, I have
comforted Zion, and heaped upon her blessings and consolations.

"Hearken unto me, my people, and give ear unto me; for a law shall proceed
from me, and I will make my judgment to rest for a light of the Gentiles."

Amos viii. The prophet, having enumerated the sins of Israel, said that God
had sworn to take vengeance on them.

He says this: "And it shall come to pass in that day, saith the Lord, that I
will cause the sun to go down at noon, and I will darken the earth in the
clear day; and I will turn your feasts into mourning, and all your songs
into lamentation.

"You all shall have sorrow and suffering, and I will make this nation mourn
as for an only son, and the end therefore as a bitter day. Behold, the days
come, saith the Lord, that I will send a famine in the land, not a famine of
bread, nor a thirst for water, but of hearing the words of the Lord. And
they shall wander from sea to sea, and from the north even t

Re: Double is doing incorrect subtraction

this opinion.

They imagine that, if they obtained such a post, they would then rest with
pleasure and are insensible of the insatiable nature of the if desire. They
think they are truly seeking quiet, and they are only seeking excitement.

They have a secret instinct which impels them to seek amusement and
occupation abroad, and which arises from the sense of their constant
unhappiness. They have another secret instinct, a remnant of the greatness
of our original nature, which teaches them that happiness in reality
consists only in rest and not in stir. And of these two contrary instincts
they form within themselves a confused idea, which hides itself from their
view in the depths of their soul, inciting them to aim at rest through
excitement, and always to fancy that the satisfaction which they have not
will come to them, if, by surmounting whatever difficulties confront them,
they can thereby open the door to rest.

Thus passes away all man's life. Men seek rest in a struggle against
difficulties; and when they have conquered these, rest becomes insufferable.
For we think either of the misfortunes we have or of those which threaten
us. And even if we should see ourselves sufficiently sheltered on all sides,
weariness of its own accord would not fail to arise from the depths of the
heart wherein it has its natural roots and to fill the mind with its poison.

Thus so wretched is man that he would weary even without any cause for
weariness from the peculiar state of his disposition; and so frivolous is he
that, though full of a thousand reasons for weariness, the least thing, such
as playing billiards or hitting a ball, is sufficient to amuse him.

But will you say what object has he in all this? The pleasure of bragging
tomorrow among his friends that he has played better than another.

RE: Double is doing incorrect subtraction

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