When you have set up the introductory
display screen, it is best to wait until the user has fully finished
reading as it can be annoying to move on to the next screen before
you have read the first. However, waiting for user response does
break the program flow and 'delay' or 'wait' statements are sometimes
best, especially if it is a display tutorial that can be LISTed
and analysed later. These delay statements take the form
FOR WAIT=1 TO NUMBER: NEXT WAlT
where NUMBER is any value that
is suitable for your program.
If you do want user response then
probably the simplest way is to monitor keyboard response. The following
example will correspond to the 'FINISHED' box.
100 ? "PRESS ANY KEY TO CONTINUE"
110 POKE 764,255 : REM *** This sets the 'last key pressed' location
to a no-key pressed condition.
120 IF PEEK (764)=255 THEN 120 : REM *** Keep looking to see if
any key is pressed.
130 ?"THANK YOU" : REM *** PEEK (764) is less than 255, i.e. a key
was pressed.
To use the 'AGAIN?' box, the computer
must be supplied with a specific answer. In this case PEEK (764)
will have to be 43 for Y(es) or 35 for N(o). Any other response
should send the computer back to look at the keyboard again.
100 ? "SAME AGAIN?"
110 POKE 764,255: REM *** Clear register.
120 IF PEEK(764)=43 THEN GOTO YES: REM *** Subroutine.
130 IF PEEK(764)=35 THEN GOTO NO
140 GOTO 120: REM *** Look again.
Another way to do this is to look
directly at the input. As some users tend to input "YES" while others
input "Y", it is necessary to look only at the first letter of the
input. Thus you need only DIM the string to one character, saving
on memory.
100 DIM A$(1)
110 INPUT A$
120 IF A$="Y" THEN GOTO YES: REM *** Subroutine.
130 IF A$="N" THEN GOTO NO
140 ? "TRY AGAIN":GOTO 110
There are other ways. to do this,
but these are about the simplest.
Let's go on now to some feedback
from the first column. I received a letter from Steven Wayne of
Palmers Green. Steven, who does some teaching, told me that I should
explain what all the POKEs are for and should use REM's more often.
I had hoped that readers would avail themselves of the PAGE 6 offer
of 'Mapping the ATARI', but if not then I will gladly run over the
listing again.
Line 5010 - POKE 559,0, as described
in the text, will switch off the screen and allow the computer to
run faster. The screen will also appear fully drawn when switched
on again. POKE 710 is one of the colour registers used instead of
SETCOLOR.
Line 5015 - POKE 752,1 will turn
off the cursor. POKE 559, 34 will turn on the screen.
Line 5040 - again POKE 559,0 to
switch off screen. POKE 712,34 another colour register (I have no
idea why I also used a SETCOLOR statement here!). POKE 756,226 sets
the characters to lower case, and POKE 752,1 to swich off the cursor.
Line 5060 POKE 559,34 - switch
on screen.
So much for the first part of
the game. This issue I have provided some additional routines in
Listing 1 which should be added to the first part of the game in
issue 18. I hope that you read the last 'FIRST STEPS' column about
LOCATE, as the program makes use of this command. The keyboard entry
is looked at (lines 1010-1100 and 2010-2100) and then compared with
the associated screen location. The value of the screen location
is then checked to see if it contains 'X' or 'O'. If it does then
the choice must be made again. If not, the relevant character is
printed in the square. To make life easier, I made the line listings
with exactly a 1000 difference (aren't I good to you?). All you
need do is change the line number and then X$ to O$ and hit RETURN.
