There's a new command
in
line
150
- INS T
R.
It
tells
the
computer to INterrogate
the
first STRing expression to find
the
first occurence of
the
second string expression,
in
other words,
it
searches N A
ME
$ (
x)
for SEA R C H $ (which is the variable you
input
in
line
130
containing
the
name
that
you're looking for).
If
INS T R doesn't find
it
(or
any
part
of it),
it
gives out a value
ofO,
which is used here to make
the
program
pass to line 1
80
and
try
again
with
the
N E X T value of x.
If
the
program
has
passed
through
all values of x up to 100,
it
then
continues to line 1
90
and
tells you
that
it
hasn't
found
the
name.
If
however
it
does find
the
name, INS T R will not produce a
value of
0,
and
the
program
will
then
pass from line 1
50
to 1
60
and
print
the
name
and
phone number,
then
END
at
line 1
70.
As you
can
see, our program is developing quite rapidly now,
but
there's still
so
much
to be done. Let's
sit
back for a moment
and
consider some drawbacks
ofthis
program,
starting
with
the
way
in
which
the
program runs:
First
you type
in
the information,
then
you
get
a
list
back,
then
you search for a specific name.
What
if?
Well,
what
if
you don't
want
to
do
it
in
that
order?
What
if
you
want
to
start
by
searching for a
name
that
you stored
in
the
program yesterday? And
what
if
you
want
to add some more
names
and
numbers to those already there? These are all aspects of
the
program
that
you have to
think
about
and
find solutions for; it's
what
programming is
all
about. As previously mentioned, BASIC is kind enough to let you
sandwich afterthoughts into
the
program,
but
a good programmer will have
anticipated
these
problems beforehand.
Another major problem
with
this
program is
that
the
values of
the
variables
in
the
arrays
are
all stored
in
a
part
of
the
computer's memory
that
is cleared whenever you
RUN
a program. You'll not
want
to have to type
in
all
the
information every time you
use
the
program,
so
you'll need
the
option of being able to save
the
values of all
the
N A M E $
and
T E L $ variables before you switch
off,
together with
the
option to load
in
the
values of
the
variables whenever you
run
the
program.
Solutions
The first
ofthese
problems (i.e.
the
order
in
which things
are
carried out) can be dealt
with
by
writing
the
program
so
that
when
it
runs, you get a choice of
the
various
functions
that
it
can perform. This type of program is called 'menu-driven', and
in
effect displays a
menu
on
the
screen from which you can select
an
option.
If
you've
ever used one of those cash dispensers outside
the
bank,
then
you'll have already
operated a menu-driven computer program! Let's add a
menu
to
this
program:
Beyond Foundations Chapter 2 Page 5
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