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Liberty BASIC Developer
Vol. 1 No. 5 November 2001
Contents:
Editors Note
LB News
Open Source: html editor
COMMAND Focus: Call/Sub
Site links
Next Month
Feed back
Legal Stuff
Editors Note
I hope that every one is doing well and getting their lives back to some level of normalance. I dont quite know were the month
of October went but it came and went quickly which is why this issue is late. There are many promising programmers out there
by the look at the message traffic that I have seen on the 3 yahoo news groups. I would like to give thanks to those who provide
help to us all in the LB community and those who bring new ideas. Don't let that grey matter go soft.
Happy Programming
Neil Tremblay
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LB News
Well it looks like we are getting closer to a beta release of LB3 if I am reading the messages correctly which have
been posted. It also appears that Carl is working on a update of LB which will be 2.03.This will fix up some of the minor bugs.
If you haven't stopped by the Liberty BASIC site recently you may wish to take a look. There is information about a new
SAMs book on programming using LB. Also Carl has an offering of online courses. As well there are links to other great
Liberty BASIC resource sites.
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Open Source: html editor Part 4
I dont know were the month went, but I did not get a chance to add any additional features to the HTML editor program. I have
been able to create a small help file for it though. And of course the help file is in html format written with the editor. You can find the
HELP file in the files section of this web site.
There is still plenty of room for refinement to this program. I would like to here from others who are using this program and
what if any changes you may have made. I will not be doing any further changes for the time being, but I will probably come
back to it a few month's from now.
Happy programming!
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- COMMAND Focus: Call/Sub
This month we are going to take a look at using the sub command. Sub is short for subroutine ( I know that this may
be obvious but it still needs to be said). In Liberty Basic, subroutines are like seperate programs. They only know
what you pass to them on calling. The only exceptions to this are handles and arrays which are global to the whole
program. Here is the syntax for a subroutine.
sub mysub variables
'some very important code goes here
end sub
Now lets go through each part of this command. The first thing is the reserved word 'sub' which tells the LB compiler that
what follows is a subroutine. The next item 'mysub', which in this instance is the name which I have given to my subroutine.
You may not name your subroutine with any reserved word! The last item in the first line is variables. You can have as many
variables as you wish,numeric and/or string or none at all. These variables are how we pass information into the subroutine
if they are needed to carry out a specific task that we assign. The second line is where we would place our code.
This could be a simple single command or a complex multi line algorithm. The last line of our sample is 'end sub'. This signals
to the compiler that it has reached the end of the subroutine and to return control to the next instruction after which it was called.
Lets start by creating a simple subroutine which plays a
predefined wave file.
sub cheer
playwave "tada.wav"
end sub
In this sample we have named our subroutine cheer, and have not assigned that it requires any variables. When this subroutine
is called it will play the tada wave file, then return control back to the calling part of the program. Follows is the line of code to run
this subroutine.
.
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call cheer
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This command has program flow temporarly redirected to the subroutine cheer. Which then performs its action of playing
our selected wave file before returning. We will now make a call and subroutine which uses a single variable.
.
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myNum = 8
call prtsq myNum
.
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sub prtsq var 'Compute and print square of a number
varsq = var * var
print varsq
end sub
In the above example we start by assigning 8 to the numeric variable myNum. We then make a call to the subroutine 'prtsq',
passing to it our assigned value of 8 in the myNum variable. Now in our subroutine prtsq, var has the assigned value of 8. It
then proceeds to assign to our variable varsq the value of var * var, which in this case will be 64. The subroutine then prints
to the main window the computed value of 64. As we have reached the end sub line, control is now returned to the first command
after our call to the prtsq subroutine. You should be aware that if we had of had the formula var = var * var that the myNum
would not be change. This would also be true if in our subroutine we had named the variable the same as in the program,
myNum. These are different variables! Another note on the above example is that we could have sent the literal '8' to the
subroutine.
In our next example we will pass a string to a subroutine.
.
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myString$ = "Liberty BASIC Programmer"
call prtLittle myString$
.
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sub prtLittle var$ 'converts string to lower then prints
var$ = lower$(var$)
print var$
end sub
This example is similar to the previous, except that we are using a string variable. Lets work through it. Our first line
assigns the string 'Liberty BASIC Programmer' to our variable myString$. Next we make a call to our subroutine
prtLittle sending along our loaded variable myString$. Our subroutine accepts this information and then proceeds to
act upon the data as we have laid out. In this instance we have decided that we want to convert our string to all
lower case, then it is printed to our main window. As before when the end sub statement is reached, control is returned
to the command immediately following our call.
With this next example, we will pass multi variables of mixed types.
.
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volts = 120
vmod$ = "units"
amps = 15
amod$ ="units"
call pwrcalc volts,vmod$,amps,amod$
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sub pwrcalc emf,emulti$,current,cmod$ ' power calc.
if emulti$="kilo" then emf = emf *1000
if emulti$ ="milli" then emf = emf /1000
if cmod$="kilo" then current = current*1000
if cmod$="milli" then current = current/1000
tpower = emf *current
print tpower
end sub
Looking at this example you will see that we have assigned values to 2 numeric variables and 2 string variables. We then
make are call to the pwrcalc subroutine, but note that our list of variables is seperated by commas. It should also be noted
that variable types in the call must match those of the sub, being numeric or string. It is the programmers responsiblity to
ensure that this is done.
There is one last example that we will look at. This is having a subroutine operate on some data and then return it to the
calling program. I do not think that this is the correct use of a subroutine and that a function should be used in its place. Using
this method with a function you can return multiple results. So
lets get started, here is our code.
.
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dim var(10)
for counter = 10 to 100 step 10
var(counter/10) = counter
next counter
call totarry
print var(0)
.
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end
sub totarry
var(0) = 0
for inc = 1 to 10
var(0) = var(0) + var(inc)
next inc
end sub
To start with we are going to dimension an array which we will use to pass information to and from our subroutine. The next
3 lines of code are used to load data into the array var(). We could just as easily assigned individual values to any number
of the elements in this array. The fourth line of our code makes the call to our subroutine totarry, notice that we did not pass
any variables into it as in this case they are implied. Now we jump down to our subroutine totarry. Here our subroutine knows
that some data will be loaded into our array. It then begins to process this data and places the sum result into the element var(0).
Upon completion it returns control to the first command following the call which in this case is a simple print statement which
displays the result in the main window.
Hopefully this explanation of using subroutines will be helpful and may even spark new ideas for its usage.
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Site links
http://www.libertybasic.com Liberty BASIC home page
HTML editor Open source, code and Help file
http://lcsoftlb.50megs.com Liberty BASIC software from the Left Coast. Editors home site
http://lbdev.5u.com Liberty BASIC Developer home page
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Next Month
- Serial Port Primer
- Command Focus: Open "COM...
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Feed back
All readers feed back is welcome whether its to do with this issue, future acticles
or comments in general. Send your message to mailto:neiltrem@hotmail.com
Any one who wishes to submit an article for publication, please send it to the editor. mailto:neiltrem@hotmail.com
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Legal Stuff
The Liberty BASIC Developer ezine and lbdev.5u.com are © Neil Tremblay 2001 all rights reserved.
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