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\input macro.tex
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\line{\sevenrm a109.tex[106,phy] \today\hfill}

\font\rmn=amr9
{\rmn
{\narrower\smallskip\noindent
Write a program that plots $\sin(x)$ and $\cos(x)$ ($0≤x≤\pi=3.14159$) on a 
single graph with~$x$ as the {\it horizontal\/} coordinate. Vertical and
horizontal scales should be $0.05$ per character. Draw the graphs of
$\sin(x)$ and $\cos(x)$ using the characters~`{\tt X}' and~`{\tt O}'
respectively. Fill the region between the graphs
(below one of the graphs and above the other) with
the character~`{\tt /}'. Superimpose the graph on a background grid at
multiples of 0.25, using the characters `{\tt -}', `{\tt |}', and `{\tt +}'
for horizontals, verticals, and crossings respectively.
\smallskip}

{\narrower\smallskip\noindent
To determine where to print the {\tt X} and {\tt O} characters, calculate
the desired line number as a {\tt REAL} expression ~E, using
{\tt ROUND({\rm E})} as the line where the letter is printed.
\smallskip}

{\narrower\smallskip\noindent
The driver of the part of the program that prints characters should look 
like this:
\smallskip}

{\obeylines\obeyspaces\let =\ \tt
        FOR R:=? TO ? DO
           BEGIN
           FOR C:=? TO ? DO
              ?;
           WRITELN
           END
}
}


\bigskip
\parindent0pt
\copyright 1984 Robert W. Floyd;
First draft March 28, 1984.

\bye