Double - Double = Wrong Answer?

[The Hobo]

I'm fairly new to VB.Net, but am fairly fluent in VB6. I have some code like this:

dblTotal = dblTwo - dblOne

Where dblTwo = 17 and dblOne = 16.94 and dblTotal ends up being equal to "0.0599999999999987"

huh?

[crptcblade]

Its a seems to be a big problem in VB6 with double precision, too.

Try casting to a Decimal...

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim d1, d2, d3 As Double
 
        d1 = 16.94
        d2 = 17
 
        d3 = CType(d2, Decimal) - CType(d1, Decimal)
 
        MessageBox.Show(d3)
 
    End Sub

[salvelinus]

That's a well known bug ("feature" in MS lingo) of floating point numbers in binary. It's the reason you don't check floating point numbers for exact equality, just for an arbitrarily small difference. Like crpptcblade says, you'll get the same problem in VB6 as well, not to mention C, C++, Java, Pascal, etc.

[The Hobo]

I switched to using the Decimal datatype and it works fine.