latex reference subfigure in caption code example

Example 1: subfigure latex

\usepackage{caption}
\usepackage{subcaption}
\begin{document}
\begin{figure}
\begin{subfigure}{.5\textwidth}
  \centering
  % include first image
  \includegraphics[width=.8\linewidth]{log_demo1.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-first}
\end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  % include second image
  \includegraphics[width=.8\linewidth]{log_demo2.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-second}
\end{subfigure}

\newline

\begin{subfigure}{.5\textwidth}
  \centering
  % include third image
  \includegraphics[width=.8\linewidth]{log_demo1.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-third}
\end{subfigure}
\begin{subfigure}{.5\textwidth}
  \centering
  % include fourth image
  \includegraphics[width=.8\linewidth]{log_demo2.png}  
  \caption{Put your sub-caption here}
  \label{fig:sub-fourth}
\end{subfigure}
\caption{Put your caption here}
\label{fig:fig}
\end{figure}

Example 2: subfigure latex

\begin{figure}
	\centering
	\begin{subfigure}[b]{0.3\textwidth}
		\centering
		\includegraphics[width=\textwidth]{first image}
		\caption{first image}
		\label{fig:ui1}
	\end{subfigure}
	\hfill
	\begin{subfigure}[b]{0.3\textwidth}
		\centering
		\includegraphics[width=\textwidth]{third image}
		\caption{third image}
		\label{fig:ui3}
	\end{subfigure}
	\label{fig:three graphs}
\end{figure}