[Tex/LaTex] the correct way to caption a `tikzpicture`

captionstikz-pgf

I have some trees drawn with tikz and I'd like to have some text associated with them. I can use \caption within figure, but not tikzpicture.

UPDATE:
Thanks for your advice. figure seems to put my first picture at the bottom of the page, and the second one on the second page. I would like these to be close to the paragraph like the tikzpicture was. Any ideas?

\par
Suppose we enter keys into a red-black tree in this order: 33, 47, 51, 50.
\begin{figure}
\begin{tikzpicture}
\node [blacknd] {33}
                child{ node [extnd] {}}
                child{ node [extnd] {}
        }
; \end{tikzpicture}
\caption{We start by adding 33 to an empty tree}
\end{figure}

\begin{figure}
\begin{tikzpicture}
\node [blacknd] {33}
                child{ node [extnd] {} }
                child{ node [rednd] {47}
                        child{ node [extnd] {} }
                        child{ node [extnd] {} }
        }
; \end{tikzpicture}
\caption{Then we add node 47. There are no imbalances to fix, since the new node's parent is black.}
\end{figure}

UPDATE: I figured it out from the excellent page here: http://en.wikibooks.org/wiki/LaTeX/Floats,_Figures_and_Captions#Figures

What I was looking for is the 'h' placement specifier.

Best Answer

You need to put the tikzpicture in a figure; the following shows the caption fine:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows}
\usepackage{caption}

\begin{document}

\begin{figure}
\centering
\begin{tikzpicture}[object/.style={thin,double,<->}]
  \draw[object] (7cm,-1cm) -- (6cm,-2cm) node[midway,above] {a label};
\end{tikzpicture}
\caption{A caption.}
\end{figure}

\end{document}
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