396 lines
8.5 KiB
Groff
396 lines
8.5 KiB
Groff
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.1
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This window will show examples of
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BetterBASIC features which are not
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available in any BASIC which you may
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be used to.
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Please try each program example on
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the computer by entering the sample
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program as shown. Use LIST and EDIT
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to display and change your program,
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and NEW or SCRATCH to delete an
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existing program from memory.
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! Strike F1 for the first lesson.
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%
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.2
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First let us explore some of the
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BetterBASIC Block Structures and the
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properties of Block Structures.
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Enter the following program:
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! 10 FOR X=1 TO 16
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! 20 PRINT BIN$(X),HEX$(X)
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! 30 GOTO 10
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! 40 NEXT
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Use the LIST command to list the
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program. Note the automatic
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indentation. Try the RUN command.
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You will see that BetterBASIC will
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not execute programs with GOTO's
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into or out of a Block Structure.
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Use 'DELETE 30' to remove the
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offending line.
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! Now try RUN
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%
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.3
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You will have noted that BetterBASIC
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lists the variables used and their
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type at the head of the program. As
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your program grows in size, you will
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find this a very useful overview of
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the variables you are using in a
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program.
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This listing will contain the names
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and types of only those variables
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actually referenced in the program.
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Variables which have been declared
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but not referenced will not be
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listed.
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To list the program without the data
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declarations use the command 'LIST-'
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BetterBASIC has a built-in Cross
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Reference Lister. Try the command
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'XREF' which will list all lines in
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which each variable is used.
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%
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.4
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Let us modify our program by adding
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the following program lines:
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! 5 DO 3 TIMES
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! 50 REPEAT
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List the program, it should now look
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like this:
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! 5 DO 3 TIMES
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! 10 FOR X=1 TO 16
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! 20 PRINT BIN$(X),HEX$(X)
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! 40 NEXT
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! 50 REPEAT
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Note that nested Block Structures
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are indented multiple levels. This
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greatly enhances the readability of
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block structured programs.
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! Use RUN to execute the program.
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%
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.5
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Next let us create a BetterBASIC
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Procedure to beep the PC's speaker.
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Let us call this procedure 'Bell'.
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Create a WORKSPACE for this
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procedure by typing the Declaration:
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! PROCEDURE: Bell
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Observe what happens. The status-
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line at the bottom of the screen
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informs us that we are now inside
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procedure Bell's workspace.
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Try the 'LIST' command. Nothing is
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listed!! What happened to our
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program? It is still there, but in
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its own workspace called MAIN. The
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display and keyboard is now attached
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to Bell's workspace which is empty.
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Commands like EDIT and LIST always
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operate in the current workspace.
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%
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.6
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Enter the following program line:
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! 10 PRINT CHR$(7);
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ASCII character 7 is the BELL
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character. When output to the
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screen this character beeps the PC's
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speaker.
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Note that we used line number 10
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even though we already had a line 10
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in the MAIN program. Each Procedure
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(and Function) workspace has its own
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set of line numbers. Return to the
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MAIN program's workspace by issuing
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the command:
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! MAIN
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Use the LIST command to satisfy
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yourself that we are now in the MAIN
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program's workspace.
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%
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.7
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Add the following statement to the
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MAIN program:
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! 8 Bell
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Note that the BetterBASIC compiler
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accepts the word 'Bell' as though
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this was a normal BetterBASIC
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keyword. LIST your program, it
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should look like this:
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! 5 DO 3 TIMES
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! 8 Bell
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! 10 FOR X=1 TO 16
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! 20 PRINT BIN$(X),HEX$(X)
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! 40 NEXT
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! 50 REPEAT
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Note that we called Bell by just
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using its name (no CALL is used).
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!Use RUN to execute the program.
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%
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.8
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Procedures are, of course, rarely as
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simple as the one-liner we just
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created. In general, Procedures
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consist of many program lines (as
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many as you need), and also in
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general require parameters or
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ARGUMENTS to be passed along as
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information to the procedure.
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Let us design a Procedure to print
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an asterisk a given number of
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positions from the left hand side of
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the screen. First declare the
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procedure:
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! PROCEDURE: Plot
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Observe that the Status Line changes
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to indicate the new workspace.
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%
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.9
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We wish to pass a parameter to Plot
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which gives the position of the
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asterisk. We declare this parameter
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as follows:
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! INT ARG: X
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This declaration does two separate
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jobs. It informs the BetterBASIC
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compiler that an integer number is
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required as an argument when Plot is
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called, and it also gives the Plot
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Procedure a means of accessing the
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actual value passed as the value of
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'X'. Now enter Plot's program:
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! 10 DO X TIMES
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! 20 PRINT " ";
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! 30 REPEAT
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! 40 PRINT "*"
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!Use the command MAIN to exit Plot.
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%
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.10
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Now modify the MAIN program by
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entering the program line:
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! 20 Plot X
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Use LIST to verify that your program
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now is as follows:
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! 5 DO 3 TIMES
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! 8 Bell
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! 10 FOR X=1 TO 16
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! 20 Plot X
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! 40 NEXT
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! 50 REPEAT
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Use RUN to execute the program. Does
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the program do what you expected ?
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!See how we use the Procedure Plot in
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!exactly the same way that we use
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!ordinary BetterBASIC keywords.
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%
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.11
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! BetterBASIC FUNCTIONS
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BetterBASIC Functions are created in
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much the same way as Procedures.
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Procedures perform actions;
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Functions may perform actions, but
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always return as VALUE.
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BetterBASIC supports three types of
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Function:
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! INTEGER Function
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! REAL Function
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! STRING Function
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Like Procedures, Functions can be
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very simple, or arbitrarily complex.
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Like Procedures, Functions can
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specify from none to many ARGUMENTS
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which must be passed when using the
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Function.
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%
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.12
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Let us create a simple Function
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named Double, which simply returns a
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value which is the argument
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multiplied by 2. Let us also assume
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that we wish to report an error if
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the argument is negative. First
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declare the Function:
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! REAL FUNCTION: Double
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This creates a workspace for the
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Function (Check the Status Line).
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The program for this function is:
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! REAL ARG:X
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! 10 IF X<0 THEN ERROR 555
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! 20 RESULT=X*2
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Note that the LAST statement is the
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RESULT statement. This is a
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requirement in Functions.
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!Use MAIN to exit from Double.
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%
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.13
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First try some immediate mode
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statements:
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! PRINT Double(12.33)
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! PRINT Double(.023)
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! PRINT Double(1+Double(23.7))
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As you can see, function calls can
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be nested. Try the following:
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! PRINT Double(1-1.23)
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Note the way BetterBASIC notifies
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you of errors. Not only do you get
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an error code and a line number,
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BetterBASIC also informs you of the
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origin of the error.
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This is important. Without this
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information it would be difficult to
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locate the source of the error.
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%
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.14
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Next modify the MAIN program as
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follows:
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! 20 Plot Double(X)
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Again, the BetterBASIC compiler
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accepts 'Double' as though it was a
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standard BetterBASIC function.
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The program should now LIST like
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this:
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! 5 DO 3 TIMES
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! 8 Bell
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! 10 FOR X=1 TO 16
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! 20 Plot Double(X)
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! 40 NEXT
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! 50 REPEAT
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! RUN the program.
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%
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.15
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! Program Listing.
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So far, we have listed each
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individual program workspace using
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the LIST command. To list all
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workspaces we use the following
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command:
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! LIST ALL
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Try it. See how all the procedures
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and functions are listed. To list
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just the names of the workspaces you
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can use:
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! LIST PROCS
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Here, the word 'PROCS' refers to
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both Procedures and Functions
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%
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.16
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Next we will show you how to create
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a BetterBASIC MODULE. To create
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such a Module, a BetterBASIC program
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which has been created interactively
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must first be saved and re-compiled
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to allow the compiler to pass
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necessary information to the Module
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Linker.
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! Saving Programs
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This sample version of BetterBASIC
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does not allow programs to be SAVEd
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to disk.
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%
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.17
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You can, however use the 'LIST ALL'
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command to save a listing of your
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program, which can be recompiled
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using the 'LOAD' command.
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Issue the following command:
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! LIST ALL "foo"
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Now clear memory by typing the
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following command: (The screen will
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blank, and after a few seconds you
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will be back to this lesson!!).
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! SCRATCH
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%
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.18
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We hope that these lessons have
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given you an idea of the power and
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flexibility of BetterBASIC. At this
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time you should probably print out
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the manual which came on your sample
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disk. It's the file called READ.ME.
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This manual will explain further
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about how to combine procedures and
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functions like the ones you just
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created into Modules. Also you can
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read about the different data types
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such as Record Variables which can
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be used for random file I/O.
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! HAPPY PROGRAMMING......
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%
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#
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