Sort and compress numerical citations

As mentioned in Latex hyperref and cite packages, packages cite and natbib are used to sort numerical citations. The usage of cite is

\usepackage{cite}

It is quite simple because you don't need to do anything more. [21,18,22,23] will be automatically sorted and compressed as [18, 21-23].

To get the same results, options needed to be provided using natbib:

\usepackage[options]{natbib}

Options can be sort&compress or compress. The former one sorts and compresses the citations and the latter one compresses the citations only. Because of the compatible issue, natbib is recommended.