How to number chapters as "x.0"

Question

The default numbering for chapters is this:

1 Chapter
1.1 Section

What I want is this:

1.0 Chapter
1.1 Section

However, if I add the zero to \thechapter, what I get is this:

1.0 Chapter
1.0.1 Section

How do I get that ".0" appended to the chapter header?

Answer 1

Define \thesection without using \thechapter, such as

\renewcommand*{\thechapter}{\arabic{chapter}.0}
\renewcommand*{\thesection}{\arabic{chapter}.\arabic{section}}

Answer 2

Expanding on @Stefan's answer for the article document class

When you are using the book document class, you have chapters, but not when using article. For that use case, you redefine \thesection as above, without redefining \thechapter, and then follow that with redefining \thesubsection instead. That gives you the same result as sought in the OP without having to use the book document class:

\renewcommand*{\thesection}{\arabic{section}.\arabic{subsection}}
\renewcommand*{\thesubsection}{\arabic{section}.\arabic{subsection}}