# [Tex/LaTex] Missing number treated as zero and Illegal unit of measure when using subfigure

subfloats

I am trying to put two figures side by side and keep getting these two errors:

Missing number treated as zero.
Illegal unit of measure.


The only way I don't get them is if I comment the {0.5\textwidth}. However if I comment it the figures stay one under the other.

\begin{figure}
\begin{subfigure}{0.5\textwidth}
\centering
\includegraphics[width=0.4\linewidth]{Figuras/SICAPI2014.eps}
\caption{SICAPI}
\label{fig.SICAPI}
\end{subfigure}%

\begin{subfigure}{0.5\textwidth}
\centering
\includegraphics[width=0.4\linewidth]{Figuras/painel_sicapi.eps}
\caption{Painel de operação}
\label{fig.painel_sicapi}
\end{subfigure}

\caption{Planta Piloto SICAPI}
\label{fig.sicapi}
\end{figure}


As @Bernard say in his comment, blank lines between sub figures tell to LaTeX: "Put them each in own line". In similar cases I wrote as follows:

\documentclass{article}
\usepackage{graphicx}

\usepackage{caption}
\usepackage{subcaption}

\begin{document}
\begin{figure}[!ht]
\centering% center subfigures in float
\begin{subfigure}{0.45\textwidth}
\includegraphics[width=\hsize]{example-image}
\caption{SICAPI}
\label{fig.SICAPI}
\end{subfigure}
\hfil% accomodate space between sub figures
\begin{subfigure}{0.45\textwidth}
\includegraphics[width=\hsize]{example-image}
\caption{Painel de operação}
\label{fig.painel_sicapi}
\end{subfigure}
\caption{Planta Piloto SICAPI}
\label{fig.sicapi}
\end{figure}
\end{document}


I didn't check where arise errors about which you complain. In above example they are not presented. How to use subfigure se package documentation or brief description in Wikibooks: LaTeX/Floats, Figures and Captions.