Sharp PC-1403 - Page 95

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Wh e n evaluati n g c omp l ex e x p r es s i o n s , t he c o m p uter f ol l ows a p re de fi n e d set o f
p rio riti es w hi c h de ter mi ne t h e s eque n ce i n w h i ch operato r s are e valu a t e d . This ca n b e
quit e sig n ific an t :
Parentheses and Operator Precedence
I f yo u are a profic i ent programm e r, th e r e a r e certai n app li ca t i on s w h e re th i s ty pe o f
operat i on can be very u s ef u l. B eg i n n e r p rog r a m m ers s ho u ld stick t o clea r , s i mp l e
Tr ue o r F alse relationa l exp r ess i o n s.
4 1 and 27 are first con v erte d i nto b ina ry num be rs. T he n , fo r ea ch dig i t , l ogica l O is l eft i f
bot h bits ar e 1 or 0 .
17 and 22 a r e f i rst co n vert e d i nto b i na ry n u mbe rs . T hen for e a ch d ig it , log i cal 1 i s left if
either bi t i s 1 . O therwise , lo g i ca l 0 is l eft.
Fo r e x amp l e , if A is 41 and B is 2 7, (A XOR B) is 50 :
41 X OR 27 is 101001 .. 41 }X OR .
0 11 0 1 1 . . 27 · operat i o n
11001 O .. 50 i n dec i ma l n um b er
17 OR 22 is 10001 .. 1 7
1
OR ti
10110
..
22
1
opera on
101 11 .. 23 i n dec i ma l numb er
Th e C OMP UT ER i m ple m en ts l og ic a l op e rat o r s as "bit wise " l ogi c a l fu nct io ns on 16 -
bit q u antn i es , (Se e no t e on r e lati ona l ex pressi o ns and Tr ue a nd False . ) In no r m a l
opera ti o n s, this is not s i gn ific a nt be c a u s e the simp l e 1 and O ( T rue and False) w hi ch
res u l t from a relational expression use s o n l y a s i n gle bi t. I f you apply a logica l op e rat o r
to a val u e other than 0 or 1 , it w or ks o n e ach bi t indepen d ent l y . For e xample, i f A i s 1 7
a nd B is 22, (A O R B ) i s 23:
(A < 9) AN D ( B > 5)
(A > = 10 ) AND N O T ( A > 2 0)
( C = 5) OR ( C =6) O R ( C = 7 )
( X > = 50 ) XOR ( X < 70 )
M or e than t wo re l a tiona l expre s sio n s c an b e combi n ed wit h the se o perators . You
s hould ta k e ca re t o u se pa r en t h eses to ma ke the in te nd e d co mpari son c lear .
F rom the equation , the f o llow in g r e sult s a re o b ta i ned:
N OT 0 = - 1
N OT - 1 = 0
NO T -2 = 1
C o n ce pts and T e rms of BASIC