Problem numbering chapter, sections

Question

I'm trying to write something in LaTeX, I would change the style of my paragraph numbering.

I would have this:

** My PDF **

My Chapter I

My section 1

My section 2

To do so, I put this code :

\documentclass[a4paper,11pt] {report}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\renewcommand{\thechapter}{\Roman{chapter}}
\begin{document}
\chapter{My first chapter}
\section { My section}
\section { My section }
\end{document}

but instead of the previous example, I get this:

** My PDF **

My Chapter I

My section I.1

My section I.2

Can someone explain me? Thanks in advance !

Answer 1

Standard section appearance takes also a value from chapter counter. Hence you should also add:

\renewcommand{\thesection}{\arabic{section}}