How to declare multiple variables with specifying type using As in VBA?

The documentation you've linked to isn't wrong, but it's written for VB.NET and not VBA.

In VBA, as you've observed, any variable declarations that aren't immediately followed by As <type> will be Variant.

Therefore you'd need to write:

Dim a As Single, b As Single, c As Single, x As Double, y As Double, i As Integer

In VBA, when you declare

Dim a, b, c As Single

What it does is equivalent to this:

Dim a As Variant, b As Variant, c As Single

I believe the best practice is to always declare variable in a separate row. It prevents this bug and also allows for faster scanning of the code. So the code would look like this:

Dim a As Single
Dim b As Single
Dim c As Single