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\input macro.tex
\def\today{\ifcase\month\or
  January\or February\or March\or April\or May\or June\or
  July\or August\or September\or October\or November\or December\fi
  \space\number\day, \number\year}
\baselineskip 14pt
\rm
\font\rmn=amr9
\line{\sevenrm a111.tex[106,phy] \today\hfill}

\medskip
\line{{\bf Example} [While]\hfil}

I want to save my money to buy a sailboat, and sail away to Tahiti. I have
a modest initial bank balance (call it {\tt FIRSTBAL}). At the beginning of each
year I~deposit a fixed amount ({\tt DEPOSIT}); at the end of the year, the bank
pays me interest, multiplying my deposit by $1+{\tt RATE}$. The boat costs 
{\tt BOATPRICE}. A~program to determine how many years are required is:

{\obeylines\obeyspaces\let =\ \tt
        READ(FIRSTBAL,DEPOSIT,RATE,BOATPRICE);
        BALANCE:=FIRSTBAL;
        COUNT:=0
        WHILE BALANCE<BOATPRICE DO
            BEGIN
            BALANCE:=BALANCE+DEPOSIT;
            BALANCE:=BALANCE*(1+RATE);
            COUNT:=COUNT+1 (* ONE YEAR HAS PASSED *)
            END;
        WRITE ('YOU MUST WORK', COUNT, 'YEARS FOR YOUR BOAT')
        END.
}

Again, the program above works correctly even when the answer is zero;
because it tests before executing the body of the iteration, it is able
to skip the body entirely.

(Note to instructor: if your students insist on using {\tt REPEAT}, show them
why it fails here when the answer is zero.)






\bigskip
\line{\copyright 1985 Robert W. Floyd; 
First draft (not published) March 15, 1985\hfil}
%revised: Date; subsequently revised.\hfill}

\bye