Commodore Plus 4 - Input;Output Statements

INPUT/OUTPUT
STATEMENTS
Input/Output (I/O) statements are used in programs to communicate
with the person RUNning the program. Before the program is run. if all
the data for the calculations is available, there is really little need for
input statements. It is often more useful if the computer can get data
from the person RUNning the program (we'll call him or her the pro
gram user). Programs are much more versatile if the data is not "set in
stone" before running them. Output statements can be used by the
computer to tell the person running the program the answers that the
computer has calculated. Obviously, output statements are vital; there
would be little sense in RUNning a program that had no output state*
ments. {Kind of like a tree falling in a forest with no one around to hear;
does it make a sound? Does it matter?)
Advanced programmers also use I'O statements to communicate with
devices instead of with the program user. You've probably done this
yourself, but not in a program—when you used LOAD or SAVE with your
Datassette or Disk drive. LOAD is basically an input statement since
the Plus 4 gets data (your program) from your Datassette or disk
drive while SAVE is an output statement, as the PI us'4 sends data to
those devices.
In this introduction to I/O statements, we will limit ourselves to a few
of the most important ones, the ones that you'll need immediately.
They are. PRINT. INPUT, GETKEY, and READ, DATA. PRINT is an
output statement, while the others are input statements
(Remember that all BASIC 1,0 statements can be found in the BASIC
Encyclopedia at the end of this book.)
Statement name: PRINT
Format. PRINT "text in quotes'
or calculations, etc.
or variables or numbers
You have used the PRINT statement often in programs in earlier chap
ters. From that, and from the format example above, you can see that
PRINT is a very versatile statement. You can use it to PRINT out mes
sages, pictures made out of graphic characters, perform calculations,
display the value of a variable, and more. Since the PRINT statement is
used so often, it pays lo learn to use it well.
Use#1 Text Display
Suppose in your program, you want to inform the user that his or
her checking account balance is negative, or that purple lizards are
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