documentclass{article}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage{lmodern}
usepackage[frenchb]{babel}

begin{document}
tableofcontents

section{s1}
section{s1}
section{s1}
end{document}

documentclass[francais]{article}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage{lmodern}

begin{document}
tableofcontents
section{s1}
section{s1}
section{s1}
end{document}