Sharp PC-1403 - Page 84

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Co m p u ters a r e m a de up of many t i ny m emory a r eas c all ed bytes . E ach byte c an be
thoug ht of as a si ng l e c ha r acte r. F o r i n stance , t h e word byte requi r es four b ytes of
me m ory b eca u se there a r e fo ur charac t ers in it. T o see h ow ma n y byte s ar e ava il a b l e
for u s e , s i m pl y ty p e i n M E M I ENTER ] . The nu m be r d i s p l ayed i s t h e n u mbe r o f bytes
a vai l a bl e for wri t ing programs . T hi s tec h niq u e wo r ks fine f or wo r ds , but is very
i n e ffi cie n t whe n you try t o s t o r e n u mbe r s. Fo r t hi s reason , num bers a r e stor e d in a
coded fashio n . T h anks t o this codi n g te chnique, your co m pu te r c an s t o r e l ar g e
nu m bers in on l y eigh t bytes . T h e la rg es t n u m ber that ca n be s t o r ed is + 9 . 999999999
E + 99.
Th e s ma ll est nu m b e r i s + 1 . E-99 . Thi s giv e s you q uit e a range t o choose from.
Ho w e v er , i f the r e s u l t o f a calcu l at i on exce ed s this range , t h e comp ut er w ill let you
kn o w by turnin g o n t he e rr or a nnu nci a tor a n d b y d i sp l ay in g t he e r ror message i n the
s cr e en. T h i s a nnunci at or i s a s m a ll E i n t he u pper ri gh t- h a nd c o r n er o f the sc r ee n . F o r
t h e e r ror me s sage , r e f er t o Appendix A . To see it ri g h t n o w type i n:
9 ~ 9 9 * 9 I ENTER I
T o g et t h e computer w o rk i ng properly again , just pre ss the !£:@ k ey . Bu t h ow d o y ou
g o abo ut s t oring all th i s i n fo r ma tion? It's r ea lly very e a sy . T h e c o mp u t er likes to u se
na me s f o r d iffere n t pi eces o f d ata . L e t's st o re th e numb e r 556 i n to t he compute r . Yo u
m ay c all t h i s num be r b y an y na m e t hat you w is h , but f or t h i s e x e r c i se , l et's use t h e
le tt er R. T he sta t ement , LE T , ca n b e u se d t o inst ru ct t he co m pu te r to a ssig n a va l ue to
a var i ab l e na m e bu t o nl y in a p ro gr am st ateme n t. H oweve r , the L ET co m ma nd is not
necessary, so we w i ll not u se it ve ry ofte n . N o w , t ype i n R = 556 a n d p r ess th e
I E N TE R I . T he c o mp u te r now h a s t he va lu e 556 ass o c i at e d wi th t h e l ett er R. T h ese
letters t h at are u sed to s t ore i nformatio n ar e ca l led variables . To see t he co n t e nt of t h e
varia ble R , pre ss t he ~ key, t h e l ett er R k e y, and the I ENTER I key . Th e co m p u te r
r es ponds b y s ho w i ng yo u th e v a l u e 5 56 on th e r i ght o f y o ur scr ee n . T h is a b ili ty c an
b ecome ve ry u seful w h e n y ou a r e wri t i ng p rogram s a n d form ul as .
N ex t , l e t's u s e t h e R v a riab l e in a s i mp l e fo rmu l a . I n thi s f o r m ul a , t he v a r ia b l e R
sta nd s fo r t h e radius of a ci rc le wh o se a r ea w e wa nt to f in d . The fo r m u la f o r t he a re a o f a
cir c l e i s : A = " * R 2 . T y p e i n R IS H I FT I ~ 2 rn I S H I FT I 00 I E N TER I . The r e s u lt is
97 1 179 . 3866 . Th i s te c hniqu e of usi ng v a riable s i n equat io n s w i ll be co m e mo r e
u nders t anda bl e a s we ge t i nt o writi n g p r og r a m s .
Variables
T hose w it h s ome compute r backgrou nd m ay notice that t h e l a s t n u mb e r ( 65535) i s the
same as t he la r ge s t n u mber i n the spec i a l group of l i mits d i sc uss e d i n t he paragraph
"Lim i ts " o n page 67 . H exadecima l n ota ti o n i s never ab s o l ut e l y necessary in using the
co mp ute r , b u t t h ere are special app li ca ti ons w h e r e i t i s co n v e n ient.
Concepts and Terms o f BASIC