It was probably a bit hard to find your messages
on the screen with that last program. Wouldn't
it be nice to be able to clear all that stuff off
the screen? "CLS", which stands for CLear Screen,
is just the ticket. You will need to put CLS
at the very top of your program to clear the screen
before you print anything.
Inserting a new line at the top.
To make CLS the first line of your program, follow
- Press the <Home> key to get to the beginning of
the current line.
- Press the <Up Arrow> key once or twice to get the
cursor to the top of the program.
- Press the <Enter> key to get a new line.
- Press the <Up Arrow> key once to get the cursor
on the new blank line.
- Type CLS
Now your program should look like this:
PRINT "Welcome to QBASIC. Your wish is my command."
PRINT "Programming is fun."
Run it. Remember, click on Run and then Start in
QBASIC's menu. You can also run the program by
pressing the <Shift> key and holding it down while
pressing <F5> (that's what Shift+F5 means on the
menu). Another handy shortcut.
That's much better. Only your message is on the
screen, which is the way it should be.
REM or '
To add documentation comments (remarks) into a program
without affecting the program flow. Also used for temporarily removing
lines of code for troubleshooting.
Simple programs, typically less than a page long, do not
usually require documentation. Once programs include subroutines and
many page of programming, commenting (remarking) the code is a good
practice. Remarks make no difference to the program but do help the
programmer to make sense of the program. Labeling a section of code by
explaining its purpose is a good tool for troubleshooting and for
understanding what the program is and how it works in general.
REM This program is very simple
PRINT "The QBasic Station"
REM The End
The apostrophe (') is a substitute for REM. It does the
exact same thing, but is shorter to type. (Maybe the writers of QBasic
saw that they had an extra character to use, so they did.)
' This program is very simple
PRINT "The QBasic Station"
' The End
Something to note is that remarks are the only type of lines that are allowed before the SUB sub_name and FUNCTION function_name
lines in subroutines and functions. If an attempt is made to add lines
ahead of the SUB or FUNCTION definitions, the QBasic editor will show
an alert that this is so.
Commenting code well takes practice and is very
rewarding during times of troubleshooting. To help you become an expert
remarker, here are some tips on using the REM (or ') statement:
- Comment large FOR...NEXT loops, explain what they do.
- Comment any range-controlling sequences. (1 < x < 10)
- Use several remark lines at the beginning of subroutines, to explain their "big picture" purpose.
- Comment anything that looks like just a bunch of numbers, such as PSET, DRAW, LINE, and CIRCLE statements
- But don't go overboard, remarking every single line in the program.