Format long number with a thousand separator in LaTeX

In order to format a long number with a thousand separator in LaTeX, you can do it manually by giving a small space with this \, or you can use the \num{} command provided by the siunitx package. This command will automatically format the long number with a thousand separator.

\documentclass{article}
\usepackage{siunitx}

\begin{document}

 Do manually with \verb|\,|:

 1\,000\,000\,000

 Do automatically with \verb|\num{}|:

\num{1000000000}

\end{document}

Output: