Commodore PET - ADDITION; Method 1: Addition via Numeric Strings

Emptying the Buffer Before a GET
This illustration of stuffing the keyboard buffer in advance is mostly a mild
surprise, and a rather pleasant one, for program BLANKET. You can save up the
characters vou
want displayed rather than keying them in one at a time in
response to the HIT A KEY message. For other programs, however, it could come
as a rude shock that idle toying with the keyboard during, say, agame cou Id
cause the game program to fetch an unwanted string of characters from the
keyboard buffer. To avoid this,
Vou can program a loop to empty the keyboard
buffer. discarding the fetched characters, before fetching an intended response
character. Implement a
GET fetch by the code example below:
95 FOR I~1T010GET C$:NEXTI: REM EMPTY KYBD BFR
100 GET C$: IF C$="" GOTO 1(10
Line 95 is the added line to empty the keyboard buffer by getting ail ten possible
characters
that might have inadvertently been "stuffed" there. Line 100 is the
standard BLANKET
GET line.
Edit program BLANKET by adding line 95
as shown above. Now press any
combination of keys
while a character is being displayed. Any stored characters
are fetched and discarded by the
GET loop, so vou will not have any automatic
display continuations
with this loop added.
TWO-KEY REPETITION
A commonly used keyboard typing technique is to hold down one key while
pressing and releasing another.
Press
KeY1
1 t
Press Release
KeY2
KeY2
Release
KeY1
Holding down one key while pressing another key is often an unnoticed, au-
tomatic typing action used during a conversion from alphabetic to graphic or
shifted mode.
But it may be expanded to other uses, su ch as repeating sequences,
to produce some interesting effects.
Two-key repetition causes
an alternating sequence of two characters. This
method
is similar to rollover because a sequence is produced, but the results are
different. The
following diagram shows what happens:
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