Mein LaTeX-Forum

\usepackage{times}\documentclass[12pt]{scrreprt}

\usepackage[latin1]{inputenc}

\usepackage[a4paper , tmargin = {2.5cm} , bmargin = {3.5cm} ]{geometry}
\usepackage{graphicx}
\usepackage{eurosym}
\usepackage{setspace}
\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage[latin1]{inputenc}


\renewcommand*{\thechapter}{\Alph{chapter}}
\renewcommand*{\thesection}{\Roman{section}}
\renewcommand*{\thesubsection}{\arabic{subsection}}  
\renewcommand*{\thesubsubsection}{\alph{subsubsection}}
\setcounter{secnumdepth}{4}
\setcounter{tocdepth}{4}  

\makeatletter

\newif\if@altsecnumbrace% vielleicht eine Klammer?
% Den automatischen Punkt umdefinieren in Punkt oder Klammer
\renewcommand*{\autodot}
{
  \if@altsecnumformat% aus der Originaldefinition
    \if@altsecnumbrace% neu
     )
     % neu
    \else% neu
      .% aus der Originaldefinition
    \fi% neu
  \fi% aus der Originaldefinition
  \@altsecnumbracefalse% neu
}

% Inhaltsverzeichniseintrag
\newcommand*\OriginalL@SubSubSection{}
\let\OriginalL@SubSubSection\l@subsubsection
\renewcommand*{\l@subsubsection}{\@altsecnumbracetrue\OriginalL@SubSubSection}

% Für den Fall, dass unten \ref{subsubsec} direkt zu "A I 1 a" führen soll,
% die nachfolgenden drei Zeilen aktivieren:
%\renewcommand*{\p@section}{\thechapter~}
%\renewcommand*{\p@subsection}{\p@section\thesection~}
%\renewcommand*{\p@subsubsection}{\p@subsection\thesubsection~}

% Gliederungsnummernformatierung in der Überschrift
\newcommand*\OriginalOtherSectionLevelsFormat{}
\let\OriginalOtherSectionLevelsFormat\othersectionlevelsformat
\renewcommand*{\othersectionlevelsformat}[1]{%
  \begingroup
    \edef\istlevel{#1}\def\solllevel{subsubsection}%
    \ifx\istlevel\solllevel\aftergroup\@altsecnumbracetrue\fi
  \endgroup
  \OriginalOtherSectionLevelsFormat{#1}%
}

% Gliederungsnummer
\renewcommand{\numberline}[1]{  \makebox[0.25cm][l]{#1}\autodot\hspace{3mm}}

% chapter
\renewcommand{\l@chapter}[2]{
  \addvspace{2ex}%                      vert. Abstand
  \pagebreak[3]%                        Seitenumbruch hier erlauben
  \noindent%                            nicht einrücken
 \makebox[0pt][l]{%                    Box für Linie
    \rule[-3pt]{\textwidth}{0.5pt}}
  {\large\textbf{#1}}\hfill#2%          Text +  Nummer
  \par%                                 Zeilenumbruch
  \nopagebreak%                         Seitenumbruch nicht erlauben
  \addvspace{1ex}%                      vert. Abstand
}

\makeatother
\begin{document}
\tableofcontents
\chapter{Chapter}
\dots
\section{Section}
\dots
\subsection{Subsection}
\dots
\subsubsection{Subsubsection}
\dots
\subsection{Subsection}
\dots
\chapter{Chapter}
\dots
\end{document}

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