\input{preamble-standalone.ltx}
\begin{document}

% Ex. No. 100 (Section 14.2.1 : Place an arrow on segment)

\begin{tikzpicture}
  \tikzset{
    arr/.style={postaction=decorate,
    decoration={markings,
    mark=at position .5 with {\arrow[thick]{#1}}
      }}}
  \tkzDefPoint(0,0){A}
  \tkzDefPoint(4,-4){B}
  \tkzDrawSegments[arr=stealth](A,B)
  \tkzDrawPoints(A,B)
\end{tikzpicture}

\end{document}