Radio Shack TRS-80 - Page 119

Note
that
we
have used the
same trick
as
above (under
Details) to
avoid negative values
ofY.
What happens if
you
change line
40
to
40
RESET
(X+126.Y)
and
RUN?
Then;
40
RESEKX+125.Y)
And
RUN.
Don't just sit there
—
try
them!
See what you
almost
missed?
EXERCISE
20-3
:
Change
the
last
two
programs
so
that they
move the
dot up and to the left
respectively.
[%
Now, let's have the dot move down until it strikes a barrier. The program is:
10
INPUT "HORIZONTAL STARTING POINT (0 TO 127) "(X
20
INPUT "VERTICAL STARTING POINT (0 TO 47) ";Y
30
INPUT
"
LOWER BARRIER"
;K
40 CLS
50 FOR M=0
TO
127
60
SET (M,K)
70
NEXT M
80
RESET (
X
, Y+47)
90
SET(X,Y)
100
Y=Y+1
I
117