Sharp PC-1403

8 5
An e x pr ess i o n i s some comb in a ti on o f v a r i ab l es , cons t an t s , and operators which ca n
be e va l ua t ed t o a s ingle v alue . T h e cal cu l at i o ns w h ic h you e ntered in Chapter 3 were
example s of exp r ess i ons . Ex p r e ss ions are an i n t rins i c part o f BAS I C programs . For
exampl e, an e x pre ssio n m i g h t be a f o rm u l a tha t c o m putes a n answer to some
equation, a te st t o determine t h e r e l ati onsh i p be t w ee n t w o quantities, o r a means to
format a set of str i ngs .
-~ ~
Expressions
(4) Variables subsc r ip t ed w ith ze r o (O) ca n n ot be defined . I f A(O) or A$(0) is
defined, an erro r wi ll r esu lt.
(5) When s ubsc ri pts g r eate r t han A (2 7 ) o r A $ (27 ) are first used, 7 bytes are used
for the v ariable n a m e , a nd 8 b y tes a r e used f or e a ch v a r i abl e .
def in e d at t he s ame time as t h e y u s e th e s ame loca ti on in the p ro g r a m /d a t a area.
( 3 ) Tw o d i mensional arrays canno t be define d , no r i s i t possible to specify the l ength
of c h aracter strings to be h e l d i n chara c ter array v a r i ables . F o r exam pl e, th e
le n gth of a character string w h i ch ca n be h eld i n c haracte r array variab l e A $( ) is
limited to seven charac t e r s o r l ess .
can not be defined at the sa m e t i m e. F e r examp l e, P. ~{ 30) and .ll.$(30) ca nn o t be
(2 ) N umeric array variab l es a n d c h a r a cter a rra y va ri a bl es w i th the same subsc ript
------ -- ------
A(30 )
- - -- - -- - - - - - - -
A ( 29 )
B C
A ( 2 8 )
A( 27 )
B ( 2 )
B(1 )
'- ·- ~ J - ~ -
[ P ro g ram / d a ta ar e a ]
If th i s program is executed , the ar r a y nam e d " A " is not d e f ined in two consec u -
tive seg m ents i n the p r og r a m da t a area , and a n e rro r w i ll result at line 40.
C on ce p ts and Te r ms of BASIC