Addition of area method to CircleT interface

Lectures/L10_ADTs/ADTs.tex

@@ -449,6 +449,8 @@ centre & ~ & pointT & ~\\
 \hline
 radius & ~ & real & ~\\
 \hline 
+area & ~ & real & ~\\
+\hline 
 intersect & circleT & boolean & ~\\
 \hline
 connection & circleT & lineT & ~\\
@@ -501,6 +503,12 @@ None
 \item exception: none
 \end{itemize}
 
+\noindent area:
+\begin{itemize}
+\item output: $out := \pi r^2$
+\item exception: none
+\end{itemize}
+
 \end{frame}
 
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