The
computer memory can be used to store all sorts of things. We have seen, so far,
that the PRINT command allows us to show letters, numbers and the results
of calculations using both letters and numbers, on the screen.
If
we want to tell the computer to remember a number, or a string of letters, then
we have to allocate some of the memory for that use.
Most
pocket calculators have a key called 'memory' which is used for remembering
numbers for later. Your computer can do much better than that: it can have as
many of these imaginary boxes in it as you like, and you write a name on each
one.
As
an example, suppose you want to remember your age! The LET command is
used (LET is the keyword on the L key): let's say it is 34
LET age=34
What happens when the LET
command is used, is that a certain section of memory is designated 'age' and the
number 34 is stored in it. To get this stored information out type
PRINT age
and back comes the number 34. It is very easy to change the contents of the 'box'
called 'age'. Type:
LET age=56
then type:
PRINT age
and 56 should appear on the screen. 'age' is an example of a variable so called
because its value may vary. It is possible to combine printing a message direct
to the screen, and the value of a variable. Type
PRINT "Your
age is "; age
However the computer is a lot more useful than just remembering numbers with names
attached to them. It can also remember strings of letters. To differentiate between
number variables and string variables - as they are called - the dollar symbol
- $ - is used at the
end of the variable name.
For
example: if we wanted to save the string of letters
"Your age is"
we could call it
a$
(string variable names can only have a single letter, other than the $,
in them). So type
LET a$="Your
age is "
If you now key
PRINT a
$ back comes the string of letters on the screen.
If
the computer hasn't been turned off since the start of this chapter type
PRINT a$;age
and see what happens.
There
are other ways of getting information into the computer's memory without using
the LET command.
For
example the INPUT command, in its simplest form, tells the computer that
some information is expected from the keyboard. Instead of typing LET
etc. everytime, you can key
INPUT age
Once the ENTER key
has been pressed a flashing 
cursor will appear on the screen. This means that the computer wants some information
from you. So type your age and then press the ENTER
key. Although nothing seems to have happened the variable has now been given the
value you typed in. Typing
PRINT age
should prove this.
Let's
combine all this together into a series of commands.
Type
LET b$="What
is your age?"
LET a$="Your age is "
INPUT (b$);age: PRINT a$;age
Note that the last line consists of two commands separated by a colon.
INPUT (b$);age
is another way of entering
INPUT "What
is your age?"; age
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