-----
INPUT Statement

        The |INPUT~ statement allows you to input from the keyboard while the
program is running.  When the computer comes to an INPUT statement, the program
stops, displays a question mark, and waits until you enter a number, then it
continues with the next line.  After the word INPUT you need to place a
variable.

        example:  10 INPUT X

        You can place a |prompt~ (words, in quotes, to remind you what to
enter) between the word INPUT and the variable.  If a semi-colon follows the
prompt, then a question mark will be displayed after it.  If a comma follows
the prompt, then no question mark will be displayed.
-----
INPUT Statement (continued)

        This is what an INPUT statement might look like in a program.

                |10 INPUT "What is X equal to";X~
                |20 PRINT X;"+ 3 =";X+3~

        Try typing in this program, running it and watch what happens.  After
you do that, change the semi-colon in line |10~ to a comma and |RUN~ it.  To
execute the program again for a different variable value, type |RUN~ and put in a
different number when the computer asks for X.
-----
String variables

        Variables can represent letters and text as well as numbers.  A
variable representing a string of letters is called a |string variable~.

        String variables are written like |numeric~ variables with a trailing
dollar sign.
                
                example: |XYZ$~="Greetings from sensible software!"
 
        You can input a string variable just like you did a numeric variable.
Try running this sample program.

        |10 INPUT "What is your name";N$~
        |20 PRINT "It's nice to meet you ";N$;", I'm the TI Professional Computer."~
-----
More on the LET Statement

        Now that you can input and output from the computer, let's really make
the computer do something.  Mathematical calculations can be performed in BASIC
with the LET statement you were introduced to in lesson one.  The LET statement
will set a variable equal to some numeric expression.  Here are the basic
|arithmetic operators~ and how they are handled in BASIC.

              FORM              DESCRIPTION             EXAMPLES
                |+~               addition              A|+~B   6|+~12
                |-~               subtraction           A|-~B   23|-~7
                |*~               multiplication        A|*~B   3|*~(2-1)
                |/~               division              A|/~B   (8+2)|/~4
                |^~               exponentiation        A|^~B   (5*3)|^~2
-----
More on LET (continued)

        Here are two specific examples of the LET statement.

                CELSIUS TO FAHRENHEIT CONVERSION

                        |10 LET F=1.8*C+32~

                YEARLY INTEREST

                        |10 INTEREST=PRINCIPLE*RATE~

        Try writing a program that lets you input a Celsius temperature and
have the computer convert it to Fahrenheit and PRINT the result.  (Use the
|INPUT~, |LET~ and |PRINT~ statements.)  Remember, the TI version of BASIC allows
you to omit the word LET if you wish.
-----
More LET (continued)

        Here is one way to write the previous program.

                |10 INPUT "Enter the Celsius temperature.",C~
                |20 F=1.8*C+32~
                |30 PRINT F;"Fahrenheit equals";C;"Celsius."~
-----
SAVE Command

        You can |SAVE~ a program on a diskette with the SAVE command.  This
will save your program so that you can retrieve and run it again.  You must
have a diskette ready for use to use this command (you can SAVE a few programs
on the BASIC Prof diskette, but you should use a different diskette for large
programs.)

        To SAVE a program, type |SAVE"name"~.  The |name~ can be anything you wish,
but must be eight or less characters with no blank spaces.

        |Invalid characters are~

                        |+ = : ; , . ?~

        Type in the following program.  SAVE it with the name "INTEREST" by
typing |SAVE"INTEREST"~.

        |10 INPUT "Enter the amount of principle.",PRIN~
        |20 INPUT "What is the interest rate (use decimal)";RATE~
        |30 INTEREST=PRIN*RATE~
        |40 PRINT "$";INTEREST;"on $";PRIN;"at";RATE;"%"~
------
LOAD Command

        The |LOAD~ command retrieves a program from the diskette and |loads~ it
into the computer's memory.  Hopefully you were able to SAVE your program from
the previous page.  The next time you want to use it, type |LOAD"name"~ (in
this case |name~ is |INTEREST~).  Typing LIST will print the program on the screen.

        Try the |LOAD~ command now and |LIST~ the program.
------
NEW Command

        The |NEW~ command |deletes~ the program that is currently in memory.
It will also clear all variables.  When you want to begin writing a new
program, you need to clear any old program remaining in the computer's memory.
Otherwise, you may get lines from the old program mixed in with lines from the
new program.

        The format for the NEW command is simply type NEW and press return.
Try out the NEW command by typing |LOAD"INTEREST"~, press return and |LIST~
the program.  Now type |NEW~ and press return and try to |LIST~ the program
again.  This will |not~ erase the program from the |diskette~, |only~ from the
computer's |memory~.
-----
End of Lesson Two

        One more lesson finished.  These first two lessons are the foundation
for the rest that you will learn.  From this point on, programming really
starts getting fun.  By the end of the next lesson you should be able to write
your own simple games, but only if you understand everything covered so far.
If you don't really understand about variables or the INPUT statement now,
review the first two lessons before you continue with lesson three.

	If you are using the BASIC Prof,		|The PC-Prof.~
let me know who you are!  Send your name		|P.O. Box 26~
and address to:						|Salina, Kansas~
							|67402-0026~

	If you like the Prof, include a contribution ($30 - $50 suggested) to
help support development of additional volumes.  Please copy and share the
Prof. with other TI P.C. users.
-----