hwo to add refercnes to latex code example

Example: cite bibliography latex

//Build a bibliography
\begin{thebibliography}{99}

\markboth{ }{\textsl{Bibliography}}

\addcontentsline{toc}{chapter}{Bibliography}
\bibitem{A} Author, \emph{Title}.
\end{thebibliography}

//Cite somewhere in the text
...as cited in the book \cite{A}