a E i - Commodore Is Awesome
a E i - Commodore Is Awesome
a E i - Commodore Is Awesome
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Whether you are entering a program<br />
from a book or magazine or you are<br />
trying to create your own masterpiece<br />
those little bugs always manage to slip<br />
their way into your code somewhere.<br />
So what do you do? Well, the first<br />
and most obvious method of debugging<br />
a program is to sit down and<br />
read it through. Even this isn't infallible,<br />
and so I speak from experience,<br />
you check it, your neighbour checks it,<br />
Freddie the family parrot even gets in<br />
one the job. But still the error hides in<br />
their somewhere.<br />
Having dealt with people's<br />
programming queries for a number of<br />
years I have noticed a several specific<br />
programming errors keep rearing their<br />
heads again and again. I hope this<br />
article will provide some tips that will<br />
help you to de-hug your programs<br />
more easily.<br />
know it Ali?<br />
Some people think that the computer<br />
is a device that is totally infallible, this<br />
isn't the case. Probably the most<br />
common problem is the fact that the<br />
computer gives you an error in a<br />
certain line number. You go to the line,<br />
check it, check it again and even get<br />
someone else to check it. Don't be<br />
fooled, just because the computer says<br />
that the error is in line X, DON'T<br />
BELIEVE IT. Your problem may be<br />
elsewhere. I shall prove this point in an<br />
example later in this article.<br />
All Blank<br />
PROGRAMMING<br />
Fault Finding<br />
Quite often people will write or type in<br />
a program, RUN it and then find they<br />
simply get a blank screen. One of the<br />
most common mistakes here is that<br />
you may not realise that the computer<br />
may be giving you an error report, it's<br />
Entering a program into your computer only to .<br />
fi nd t h a t<br />
it doesn't work is extremely frustrating. Here are a few<br />
tips on some of the most common problems.<br />
By Stuart Cooke<br />
just that you can't see it. A small<br />
example will illustrate just what I<br />
mean. Type the following into your<br />
cornputer:<br />
10 POKE 53280,0:POKE 53281,0<br />
20 PRINT "[ BLACK] HELLO<br />
WORLD"<br />
Line 10 should be replaced with the<br />
following if using a CIO, Plus/4 or<br />
C128.<br />
10 COLOR 0,1:COLOR 4,1<br />
Don't forget items in square brackets<br />
are mnemonics for <strong>Commodore</strong><br />
control codes. Read Listings if you are<br />
not sure about this. [BLACK] means<br />
press the CONTROL &I keys at the<br />
same time,<br />
RUN this program and see what<br />
happens. The program works OK, you<br />
simply can't see the message that is<br />
printed since it is printed on a black<br />
background with black text. Line 10<br />
simply sets the border and screen to<br />
black.<br />
Now this program works without<br />
any problems, but what would happen<br />
If there was an error in there? Let's add<br />
a line to the above example:<br />
30 THIS WILL CREATE AN<br />
ERROR<br />
As you are no doubt aware this line<br />
will cause a SYNTAX ERROR when<br />
the program is RUN. Let's RUN it and<br />
see. What happened? Nothing seemed<br />
to happen, your screen is still black.<br />
The error message will be printed out,<br />
you simply can't see it as it is in black<br />
on a black background. If we change<br />
the colour of the text in line 20 then all<br />
should become apparent. Change line<br />
20 to:<br />
20 PRINT "[WHITE] HELLO<br />
WORLD"<br />
YOUR COMMODORE january 1987<br />
109<br />
Remember what I said about square<br />
brackets.<br />
Now RUN the program and you<br />
will see the SYNTAX error message<br />
appear.<br />
You mayu think that this is an<br />
extremely simple error and that everyone<br />
should spot it. It may be simple but<br />
is overlooked surprisingly often.<br />
Cl28 owners have a further<br />
problem. the FAST command. For<br />
those of you not used to this command<br />
it simply turns off the display of the<br />
C128 which means that the computers<br />
speed will increase. You can still print<br />
to the screen, but you can't see what<br />
you put on it. So what would happen if<br />
the computer came across an error?<br />
You would get the same effect as<br />
above. The error message will be<br />
printed to the screen you just won't be<br />
able to see it. As a general rule of<br />
thumb, when entering a C128 program<br />
omit all FAST statements until you are<br />
sure that the program is working<br />
correctly. Then put the FAST<br />
statement back in,<br />
If you own a Cl28 then you could<br />
try the following program to demonstrate<br />
this:<br />
10 FAST<br />
20 PRINT "HI THERE !"<br />
30 I'M GOING TO CAUSE AN<br />
ERROR<br />
Now RUN the program. The program<br />
will print out the message in line 20 and<br />
line 30 will generate an error message,<br />
you simply can't see it.<br />
Enter the following command on<br />
the keyboard. You won't be able to see<br />
it so type carefully:<br />
SLOW<br />
Your screen will now come back on<br />
and you will see both the 'HI THERE!'<br />
and the error message.
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