Apple Orchard 1980 Fall v1n2 reduced

PAGE 56
the ASCII chart in them, usually in
an appendix . We strongly
recommend that you check out
your own computer's ASCII.
NUMBER, PAH-LEEZ.
If line 300 had called for an
address usually beginning with a
number then we could use the
same basic format as line 680
changing the parameter values to
reflect "O" as the lowest acceptable
input and "9" as the highest:
IF LEFT$ (IN$,1) => "O" AND
LEFT$ (IN$, 1) = < "9" THEN
GOTO NEXTPHRASE
Naturally, you'd .change the
subroutine to reflect that what's
wanted is a number rather than a
letter.
It's easy to include exceptions in
the line. Let's say that the address
could begin with the word BOX, as
in a post office box:
IF LEFT$ (IN$, 3) = "BOX" OR
(LEFT$ (IN$,1) = >"O" AND
LEFT$ (IN$, 1) = "15" THEN
GOTO REJECT
The same format can be used for
any range of individual characters
or strings.
The observant reader (you clever
person, you!) will note that even in
those cases where we want a
number we use a string input.
There are two basic reasons for this
apparantly cavalier use of strings.
First, strings are easier to
manipulate. LEFT$-RIGHT$-MID$
functions don't work on integers
and reals, and these string
functions are the most convenient
ones in BASIC to use for error
trapping. And secondly, many
BASICs will give a HARD rejection
FALL 1980
if a non-numeric character is
entered when a numeric variable is
used to accept an input. That
means, friend, that your program
might crash and burn. A string
variable, on the other hand, usually
will accept anything.
LEADING/TRAILING SPACES
There is a negative side to this
lack of discrimination on the part of
string variables. Since they accept
whatever is typed, they will accept
inadvertant hits of the space bar.
The string "gobble" is NOT the
same as the string" gobble". When
the computer looks at "gobble"
the first thing it sees after the quote
mark is ASCII 71 - what we see as a
G. But when it looks at " gobble"
the first thing it sees is ASCII 32, the
space. That means that the name
" Martha Mayno" will NEVER be
found in a data base searching for
"Martha Mayno". Goodness
knows we don't want to lose poor
Martha!
Since the example we've been
using is supposed to be part of a
name and address data base, we're
concerned
about extraneous
spaces. So we'll add the following
lines:
710 IF LEFT$ (IN$, 1) < > "
"THEN 740
720 IN$= RIGHT$ (IN$, LEN (IN$)
- 1 )
730 GOTO 710
This code eliminates leading
spaces from a string. It keeps on
looping until all leading spaces are
gone (just in case more than one
got in). You'll also want to check for
trailing spaces (since "Martha
Mayno "will be lost forever) which
can be done using similar code. The
only real change is the substituting
of BASIC's RIGHT$ function for
LEFT$ (which works the same way,
except backwards - see your
BASIC manual for details). The
following two lines of code are
based on the way APPLESOFT
handles the "truth" of IF-THEN
statements: if the condition is false
the program goes to the next line,
as opposed to the next statement.
Thus we can write:
710 IF LEFT$(1N$, 1) =""THEN
IN$ = RIGHT$ (IN$, LEN (IN$)
- 1 ) :GOTO 710
720 IF RIGHT$ (IN$, 1) =""THEN
IN$ = LEFT$ (IN$, LEN (IN$) -
1): GOTO 720