Add dot after chapter title (scrreprt document)

Question

I have a problem with the numbers added to the chapters of my document: There is no dot after the number, e. g. "2 Theory" instead of "2. Theory". I tried adding a dot before the chapter title but then it looks like "2 . Theory". I also tried \documentclass[a4paper,11pt,numbers=endperiod]{scrreprt} and %\renewcommand{\thechapter}{\arabic{chapter}.} but both add a dot after every number, even "1.1. Title" where I want "1.1 Title".

My document looks like this:

    \documentclass[a4paper,11pt]{scrreprt}

    \usepackage[utf8]{inputenc}
    \usepackage[ngerman]{babel}
    \usepackage[T1]{fontenc}
    \graphicspath{{img/}}
    \usepackage{fancyhdr}
    \usepackage{lmodern}
    \usepackage[T1]{fontenc}
    \usepackage{caption}
     \usepackage{textcomp}

    \addtokomafont{section}{\small}
    \addtokomafont{subsection}{\small}
    \addtokomafont{subsubsection}{\small}


\begin{document}
\include{theory}
\include{experiment}
\end{document}

Answer 1

If sections, subsections etc. should not get a dot after the number, use option numbers=noenddot. One possibility to add the dot after chapter number is

\usepackage{xpatch}
\xpatchcmd\chapterformat{\autodot}{.}{}{\PatchFailed}

\DeclareTOCStyleEntry[
  entrynumberformat=\entrynumberwithdot
]{chapter}{chapter}
\newcommand*\entrynumberwithdot[1]{\def\autodot{.}#1}

Example (with additional remarks):

\documentclass[
  %a4paper,11pt,% default
  numbers=noenddot% default value: autoenddot
]{scrreprt}
%\usepackage[utf8]{inputenc}% needed with older TeX distributions
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage{graphicx}% <- added
\graphicspath{{img/}}
\usepackage{fancyhdr}% it is suggested to use package scrlayer-scrheadings
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage{caption}% maybe you can use KOMA-Script commands?
\usepackage{textcomp}

\RedeclareSectionCommands[
  font=\small
]{section,subsection,subsubsection}


\usepackage{xpatch}
\xpatchcmd\chapterformat{\autodot}{.}{}{\PatchFailed}

\DeclareTOCStyleEntry[
  entrynumberformat=\entrynumberwithdot
]{chapter}{chapter}
\newcommand*\entrynumberwithdot[1]{\def\autodot{.}#1}

\usepackage{blindtext}% only for dummy text in the MWE

\begin{document}
\tableofcontents
\Blinddocument
\end{document}

Answer 2

you can use the koma option

numbers=enddot

so the first line will be

  \documentclass[a4paper,11pt,numbers=enddot]{scrreprt}

Edit:

This will set points also after section numbers.

You may want to go with: Remove last dot in title numbering

This is a solution specifically for KOMA-Script

Answer 3

This should work in every documentclass and it is based on my answer here

\documentclass[a4paper,11pt]{scrreprt}

    \usepackage[utf8]{inputenc}
    \usepackage[ngerman]{babel}
    \usepackage[T1]{fontenc}
    %\graphicspath{{img/}}
    \usepackage{fancyhdr}
    \usepackage{lmodern}
    \usepackage[T1]{fontenc}
    \usepackage{caption}
     \usepackage{textcomp}

    \addtokomafont{section}{\small}
    \addtokomafont{subsection}{\small}
    \addtokomafont{subsubsection}{\small}

\let\oldchapter\chapter
\makeatletter
\def\chapter{%
\def\thechapter{\arabic{chapter}.}%
\@ifstar{\@Starred}{\@nonStarred}%
}
\def\@Starred{%
\@ifnextchar[%
{\GenericWarning{}{Warning: A starred section can not have parameters. I am going to ignore them!}\@StarredWith}%
{\@StarredWithout}%
}      
\def\@StarredWith[#1]#2{%
\oldchapter*{#2}%
\def\thechapter{\arabic{chapter}}%
}
\def\@StarredWithout#1{
\oldchapter*{#1}%
\def\thechapter{\arabic{chapter}}%
}
\def\@nonStarred{%
\@ifnextchar[%
{\@nonStarredWith}%
{\@nonStarredWithout}%
}
\def\@nonStarredWith[#1]#2{%
\oldchapter[#1]{#2}%
\def\thechapter{\arabic{chapter}}%
}
\def\@nonStarredWithout#1{%
\oldchapter{#1}%
\def\thechapter{\arabic{chapter}}%
}
\makeatother

\usepackage{blindtext}% only for dummy text in the MWE
\begin{document}
\tableofcontents
\Blinddocument
\end{document}

Adding in order to be able to help people with other document classes or even for the OP's request if he would like to be able to change documentclass later.