Sharp PC-1500 - A Clo.er Look at some Old Friends; The LET Statement; The PRINT Statement

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F. A Closer Look At Some Old Friends
Now that we know how to enter , run, and edit pro9rams, we shall expan d our vocabul ary of
useful statem ents and commands. Let's bc,g in by examining some old friends: the NEW
command, the LET statement, and the PR I NT statement.
F . 1. The NEW Command
As \Ye saw in our p revi ous p rogrammin g exampl es, the NE\iV command del et.es all program l ines
currently in memory. We will use the NEW command (in PROgram mode) before each sample
pro gram to i ns. ur e that the on ly instructions in SHARP's memory arc the instructions of our
current program. Although it is possible {and often desirable) to have several programs in memory
simultaneously, we will postpone the use of this feature to avoid con fusion.
In PROgram mode, issue the NEW command . What effect do the Up and Down Arrow keys
have now?
F.2. The LET Statement
Don't be ala·rmed if you don't recognize the LET statement as an "o ld friend"; I sneaked this
one in on you. Actually, the LET stateme nt is nothing but the Assignment statement in disguise.
{If you don't recognize the Assignment statement either, please re-read the sectio n on vnr iablcs,
in Chapter 2, ir runed iately! ).
In the early days of BASIC eve ry stat ement began with a " k eyword" {like PR INT, INPUT, etc .)
which indicated
what th e instruction did. LET was the keyword which ide nt ified the fact that a
value was to be sto red into a variable. Today, it is generally agreed that the wo rd LET is not really
needed. As a r. esult, the k eywo rd LET is optional in PC·1500 BASIC. Thus, a st atement which
stores
the number 7 into a variable Scan be written in either of the following ways:
s = 7
or=1
L
LET S = 7
The
one excep tion, the place where LE T must be u se d, is an assignment which occ urs as part
of an IF staterrnent. Although we have not yet d iscuss ed the IF st at ement, th is should be possible
to exp lain (cros$ your fingers).
Using the IF stat em en t you can write an instruct i on like the following:
.!£. expression THEN stat emen t
If the statement following the T HEN is an Assignment statement, the keyword LET must be
used. This wou ld result in a statement with the form:
_!£_expression T HEN LET variable·name = exp ression
NOTE : Omitting the LET in this case would produce an ERROR 19 (or other error message).
F.3. The PRINT Statement
For mo st of the pr ograms you write, the instructions will fo llow a basic pattern {no pun
intended). There will be instructions to read in r aw data, instructions to process the data, and
instructions
to print or display th e results. This pattern has been referred to as the Input,
Processing, Output cycle.
The PRINT sta t ement is th e main state ment used to produce output. It is no t surprising,
therefore, that the PRINT statement has several diff erent variations. The general form at of the
l'RINT statement is the wo rd PRINT followed! by an item or a li st of ite ms to be printed. These
i nc lude character strings, expressions. or names of var iables whose values "·1ill be printed. Each
item in a list is separated by a comma or a sem i.:olon.
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