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     ALL ABOUT VARIABLES

Since you're a curious person
(after all, you made it this far),
you're probably wondering how the
computer asks for and remembers
your name. Stay tuned.  This
section will teach you how that's
done.
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The computer's memory is a lot
like hundreds of mailboxes.
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Each mailbox can contain
different information.
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And each mailbox has a name that
sets it apart from other boxes.
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These mailboxes in memory are
called variables.
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And the name given to each box in
memory is called a variable name.
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A variable name is made up of
letters and numbers.  For this
example, we've chosen the name A
(which just happens to stand for
Apple).
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For the variable A to be of any
use to you, you must assign
some information to it.  The
question is, how do you assign
information--such as numbers,
words, or equations (like 3+4)--to
a variable?
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One way to do this is to use
the LET statement.  The LET
statement assigns information
(in this case a number)
to the variable.
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The LET statement looks like
this...
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First, you must type a line
number.  In this case, line 10.
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Next, you type LET...
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followed by the variable name.
In this case, A.
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The next step is to type an equal
sign (=).
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Then type the number you want
to assign to the variable.
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The number 33 is now stored under
the name A.  Now instead of asking
the Apple II to print 33, you
can ask it to PRINT the contents
of A, which is 33.
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Do you know what to type to tell
the computer to print the contents
of A?  If so, type it now on line
20.  (If you're not sure what to
do now, press RETURN for a hint.)
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You did it!  To complete your
three-line program, type an END
statement on line 30.
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You're becoming a first-rate
programmer!  Now run the program
and look at the result of your
work.
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Congratulations!  You've just
written a program using variables.
Would you like a bit more
explanation of how this program
works? (Y/N)
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Variables are somewhat exclusive
in that they hold only one thing
at a time.  If you assign a new
value to the variable A, the
old value is replaced.
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Try it yourself.  Replace the
old LET statement on line 10 with
a new one and assign different
contents to A.
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Now run the program and notice
the new contents of A.
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See, we weren't kidding.  The
contents of variable A changed
from 33 to
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There are two ways to assign
information to variables.  You
just learned how to assign
something to a variable inside a
program.
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One way to change the contents
is to rewrite the LET statements
whenever you want to change the
numbers.
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The second way is to let you
enter information from the
keyboard while the program is
running.  This involves using the
INPUT statement.
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First of all, please clear the
computer's memory.  (Press RETURN
for a hint if you're not sure of
what to do.)
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Good job.  You're doing well.
We've taken the liberty of writing
a number game program to help
explain the INPUT statement.
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We saved the program on the disk
under the name NUMBER. Please
load the NUMBER program now.
^
