Why is it in vb.net if I assign a number to a single variable it does not equal the same value

Question

I have been searching the internet trying to understand in its simplist form why this behavior happens.

Dim mysingle As Single = 456.11
Dim mybool As Boolean = mysingle = 456.11

In the lines above mybool becomes false. I found this behavior when putting the single into a double I found extra digits showing. The .net documentations states a single is an approimate value :S

I gatehr a single is a 32bit floating point number? But why are extra digits appearing when I have explicitly said what the number is.. surely the memory should store that numbers either side of my number are 0 to fill up the memory location?!

My brain is fried on this one :(

Answer 1

The value being compared in the second statement isn't considered a Single, rather it's being treated as a Double. Since you're using VB.NET you can suffix it with a ! to force it to a Single and this will return True:

Dim mysingle As Single = 456.11
Dim mybool As Boolean = mysingle = 456.11!

Answer 2

I recommend reading: What Every Computer Scientist Should Know About Floating-Point Arithmetic.

It explains the issues with precision in floating point math in detail. For a simpler variation on the above, see The Floating Point Guide.