Error with square bracket in table

Question

\begin{table}[ht]
\makebox[\textwidth][c]{
    \begin{tabular}{ccccc}
        \hline
        \hline
        [] & [] & [] & [] & []\\
        [] & [] & [] & [] & []\\
        \hline
        \hline
    \end{tabular}
}
\caption{test}
\end{table}

I cannot run the above code, latex returned an error about missing number, but I can't see anything I am missing.

And the weirdest thing is that

\begin{table}[ht]
\makebox[\textwidth][c]{
    \begin{tabular}{ccccc}
        \hline
        \hline
        [] & [] & [] & [] & []\\
        \hline
        \hline
    \end{tabular}
}
\caption{test}
\end{table}

This code works.

Anyone have any idea?

Answer 1

Since \\ allows an optional argument, the [ in the following line is mistaken for it.

......         \\\relax
[whatever] ... \\

Answer 2

Another option is to add brackets around, like this:

{[} .... {]}