`Double`

In VB.NET a Double is 8 bytes—the size of 2 Integers. It is a value type. The Double stores numeric values that have a decimal place.

Double stores extremely small and large numbers. Doubles are often used in VB.NET programs that also use the Math type.

Example

In Main, the program assigns a Double to the value 1.5. We then display this to the Console. Next, the same variable (a location in memory) is assigned the value -1.5.

Note The Double type stores signed numbers—even signed fractional numbers. We then evaluate some expressions that use this Double Dim.

Note 2 An expression context does not change the value stored in a variable. It evaluates to a new value on the evaluation stack.

And These new values are passed to the Console.WriteLine Sub. Then they are forgotten.

Info The minimum value of a Double is a big negative value. And conversely the maximum value is highly positive.

Module Module1
    Sub Main()
        ' Use Double Dim.
        Dim number As Double = 1.5
        Console.WriteLine(number)

        ' Negative Double.
        number = -1.5
        Console.WriteLine(number)

        ' Evaluate expressions.
        Console.WriteLine(number = -1.5)
        Console.WriteLine(number + 1)
        Console.WriteLine(number.GetType())

        ' Min and Max.
        Console.WriteLine(Double.MinValue)
        Console.WriteLine(Double.MaxValue)

        ' Memory usage per Double.
        Dim b1 As Long = GC.GetTotalMemory(False)
        Dim array(1000 * 1000) As Double
        array(0) = 1
        Dim b2 As Long = GC.GetTotalMemory(False)
        Console.WriteLine((b2 - b1) / (1000 * 1000))
    End Sub
End Module1.5
-1.5
True
-0.5
System.Double
-1.79769313486232E+308
1.79769313486232E+308
8.00004

Memory usage

We use the GC type to figure out how much memory the program is using. Then we allocate an array of one million Double elements.

Result We measure the memory again. This gives us the total memory used by one million Double elements.

Info After division, a single Double is found to require 8 bytes of space. The excess bytes are for the array reference itself.

8 bytes

`Single`

A Single is a floating-point number like Double, but with less precision. It has half the bytes—so it requires 4 bytes. This simple program shows the Single keyword.

Module Module1
    Sub Main()
        ' Use Single type.
        Dim number As Single = 10.35
        Console.WriteLine(number)
    End Sub
End Module
10.35

A Double is the size of two Integers put together. It is technically a Structure. It stores a decimal place and represents a much larger range of numbers than an Integer type.