TiKZ circle

[dwsmith]

\begin{tikzpicture}
\draw (0,0) circle (1cm);
\end{tikzpicture}

How do I add directional arrows going counterclockwise on the circle?

 

[Bacterius]

Try something like this:

\begin{tikzpicture}
\draw (0,0) circle (1cm);
\draw[->, blue, thick] (1.2cm, 0) arc [radius = 1.2cm, start angle= 0, end angle= 70];
\end{tikzpicture}

Note the first coordinate before the arc command is where you'd like the arc to start, not the arc's center. I find this kind of a stupid decision, but that's the way it is. The arrow is specified by -> in the draw qualifiers.

If you want a clockwise arrow, you can have the arc go backwards (or you can use <- instead, <-> gives you bidirectional arrows):

\begin{tikzpicture}
\draw (0,0) circle (1cm);
\draw[->, blue, thick] (1.2cm, 0) arc [radius = 1.2cm, start angle= 0, end angle= -70];
\end{tikzpicture}

If you want the arrow to exist on the circle, then you can just overlap them:

\begin{tikzpicture}
\draw (0,0) circle (1cm);
\draw[->] (1cm, 0) arc [radius = 1cm, start angle= 0, end angle= 70];
\end{tikzpicture}

And you can also get artistic :

\begin{tikzpicture}
\draw (0,0) circle (1cm);
\foreach \x in {0.2,0.4,...,4.0} \draw[->, ultra thick, red] (\x + 1, 0) arc [radius = \x + 1, start angle= 0, end angle= 70 + \x * 45];
\end{tikzpicture}