17 Bit Software 6: Level 6/17 Bit - Level 6 (1998)(Epic Marketing)[!].iso/quartz/q0970.dms/q0970.adf/basic.doc

Text File | 1992-09-02 | 36KB | 1,070 lines

FESBasic/basic.doc

CONTENTS
========

    1.  Overview

    2.  Expressions

    3.  Control Constructs

    4.  Statements

    5.  Final Points


************************************************************************
========================================================================
                                1 Overview
========================================================================
************************************************************************

1.1 Preamble
============

This file contains a description of the FESBasic Programming language.
I have tried to be as complete as possible in my description of the
language as I could in this file so I must apologize if in some places
I appear to be stating the obvious, and in others going into excessive
technicalities.

I suggest that this file be browsed rather than read. Anyone with a
moderate knowledge of BASIC should probably skip to section 5 then look
at the example files and use the on-line help facilities, then refer to
this file only when absolutely necessary.

Persons with little or no previous knowledge of computer programming
will probably find this document too "technical" to be of much use. The
best advice I can give is too find a friend who knows about BASIC, then
play around with this program, contacting your friend when ever you are
stuck.

By the way the HelpFile can be browsed through by just double-clicking
its icon. It consists of a list of all the commands and functions in
FESBasic along with descriptions of each one's usage.

1.2 The Language
================

FESBasic is a modern version of the BASIC Language. Like most modern
BASICs there are no line numbers, so commands like GOTO are rarely used.

Without line numbers control constructs like FOR...NEXT and DO...LOOP take
a much higher importance. As do Procedures and user defined functions. FES
BASIC offers  rich choice of these to the programmer, allowing the creation
of well structured programs. In addition the editor automatically formats
your programs to give them that 'structured' indented look.

It must be pointed out at this stage that work is still continuing on the
Language. See the "Register.doc" file for more information about getting
hold of the latest version of the language.

Probably the best way to start this file is with an example:-

'FES BASIC EXAMPLE PROGRAM
'Doesn't do much, but what do you expect?

FOR k=1 to 10
  COLOR k   'Comments can be placed on any line
  PROC Put_Text "Line %d",k
NEXT
STOP

DEFPROC Put_Text text$,number
  LOCAL a$
  a$=FORMAT$(text$,number)
  PRINT a$
ENDPROC

<<<THE END>>>

That should give me enough to talk about for a few paragraphs.

Comments can be placed on any line. A comment is signalled by a '
and continues until the end of the line.

The editor automatically indents your code for you.

Your programs automatically get their own screen for their output.


*************************************************************************
=========================================================================
                            2 EXPRESSIONS
=========================================================================
*************************************************************************

An expression can be used almost anywhere a value is required in FESBasic.

An expression can consist of:
    Constants   eg    1    -4     "hello"
    Variables   eg    a   hello&  MyString$
    Operators   eg    +  -  *  /  =  <  <= AND OR
    Functions   eg    RND VAL STR$ INC AND
    Brackets          ( )
    UserFuncs   eg    FNxyz  FNabc$

Lets consider each of these in turn.

2.1 Constants
=============

There are three types of constant: int , long and string.

An int constant consists of an optional minus sign followed by up to 5 digits
(0123456789). An int constant must be in the range -32768 to 32767.

A long constant is like an int but it is followed by a & (eg 65538& ), unlike
int constants a long can be any size between -4294967296 and 4294967295. If
you type a number too big for an int then the editor will automatically add
the & to make a long. Arithmetic involving longs is slower than that involving
only ints.

A string constant is started by a " and is terminated by the same.

2.2 Variables
=============

Like constants a variable can be any of three types, int long or string.

Int variables consist of a letter followed by 0 to 18 alphanumeric symbols,
the underscore _ and the 'at' symbol @ are considered to be letters for this
definition. So valid names are
    x
    abc
    Hello
    Hi_There
    @

But invalid names include:
    3_blind_mice        as it starts with a digit
    a_very_long_name_that never_seems_to_end     as it's >19 characters
    a+b                 it contains a +

Int variables store only whole numbers in the range -32768 to 32767.

Long variables have similar names to ints but they must end with a &. This
is included in the 18 alphanumeric symbols, again the total name cannot be
more than 19 characters. A long can store whole values in the range
-4294967296 to 4294967295.

As you have probably guessed by now a string variable name consists of the
same restrictions as an int but must end in a $
A string variable can store up to 100000 characters of text.


A value is placed in a variable by an assignment. This takes the form

variable_name = expression

on a line of its own. 'expression' must be of the same type as variable_name
(ie both ints or both strings), but some flexibility is allowed with ints and
longs, if a conversion is possible then one will be made, so it is acceptable
to write

a&=5

despite a& being a long variable and 5 being an int constant.

2.3 Operators
=============

Operators combine the value of two sub-expressions (called operands)
relational and boolean. There are also similar operators for strings.

2.3.1 Arithmetic Operators
--------------------------

Arithmetic operators combine two numbers together to form a third. The
returned value will be a long unless both operands are ints when the return
value will be an int.

There are 4 Arithmetic Operators

    +       Performs Addition of the two operands
    -       Performs Subtraction
    *       Multiplication
    /       Integer Division ( fractions are ignored)

When an expression contains both multiplication/division and
addition/subtraction then the Multiply/Divides are done before the add/subs.

so  3+5*6  is 33 not 48
and 5+3/4  is 5  NOTE in Integer division 3/4 is zero.

To perform additions first use brackets

eg (3+5)*6


2.3.2 Relational Operators
--------------------------

A relational operator compares the values of its two operands and returns a
the int 'one' if some relationship is true, or zero if the relationship is
false.

The available relational Operators are

    <       Less Than
    >       Greater Than
    =       Equal
    <>      Not Equal
    <=      Less than or equal
    >=      Greater than or equal

Relational operations are performed after arithmetic ones , so

      5+8<7*3     gives a value 1
and   b*a<>b*b    gives 1 unless 'a' and 'b' are equal.

2.3.3 Boolean Operators
-----------------------

A boolean operator tests its two operators for "truth" (true being defined
as any value except zero) and gives a value based on the "truths" of both.

The three Boolean Operators are

    AND     Gives '1' if and only if BOTH are true, else gives '0'
    OR      Gives '1' if either or both are true , else 0
    XOR     Gives '1' if one but not both are true, else 0

Boolean operators are evaluated after relational ones.

NOTE: Unlike some other BASICs FESBasic's operators are 'logical' not
'bitwise'. ie   5 AND 4  is 1 not 4.

2.3.4 String Operators
----------------------

There are less operators that can be applied to strings than to numbers.

For 'Arithmetic' operators the only one available is 'concatenation' +
This operator joins two strings together, ie "egg and "+"chips" gives
"egg and chips"

All the relational operators can be applied. For comparison a one string
is less than another if its first letter's ASCII code is less than the
second strings first letter. If the first letters are the same then the
comparison is made on the second letter, then the end of one string is
reached.

So the following relationships are all true:-

    "chips" < "egg"         c comes before e
    "Egg" < "chips"         Capitals come before lower-case
    "2Chips" < "egg"        Numbers come before letters
    " Egg" < "chips"        Spaces come before letters.
    "chips"<>"CHIPS"        The case's are different so not equal
    "chips" = "chips"       Identical.

Most basics do not allow Boolean operations on strings. FESBasic contains
an extension to the language to allow:-

    string AND number   gives   string if number is 'true'
                                 ""    if number is 'false'

    string1 OR string2  gives   string1 if string1<>""
                                string2 if string1=""

These can be occasionally useful:

OTHER BASIC:    c$=a$
                IF a$="" then c$=b$
FES BASIC:       c$=a$ OR b$

OTHER BASIC:    PRINT "There are ";n;" cat";
                IF n<>1 THEN PRINT "s";
                PRINT " on the roof"
FES BASIC:      PRINT "There are ";n;"s" AND n<>1;" on the roof"



2.4 Functions
=============

A function takes zero or more values (called parameters) and produces a
single value as a result (known as the return value).

If a function takes two or more parameters then the function name must be
followed by a '(' and each of the parameters must be separated by commas
so for example BTST(a,3).

For a function with just one parameter the brackets are optional, so it is
acceptable to write ABS(x) or ABS x

For functions with no parameters there must not be brackets, eg TIMER

Each individual function specifies how many parameters it takes and of what
type each must be. It is an error to provide the wrong number or types, and
the computer will give an error message, either when the program is executed
or as the line is entered.

Functions are evaluated BEFORE operators so     ABS a+b
means (ABS a)+b   not    ABS(a+b).

For a complete list of the functions available in FESBasic refer to the
"FESBasic_HelpFile", where they are all listed alphabetically with descriptions.

I will now briefly describe the more interesting/useful functions:-


2.4.1 String Manipulation
-------------------------

If we have a string ( for example h$ or "hello") we may need to split it up
into smaller pieces. All BASICs provide functions to do this.

The most general one is MID$. This takes as parameters the string to be
sliced, a position to start and a length. It then returns a string made up of
a part of the initial string.

so  MID$("Hello",2,3)   gives "ell"     e being the 2nd letter and continuing
                                        for 3 characters.

If the second number is left out then the string continues to the end of the
first string, ie  MID$("Hi There",4)  is "There"

FESBasic also allows the second number to be specified as a position, so you
can write MID$("Egg and Chips",5 TO 7)  to get "and".

Other available functions are LEFT$(a$,n) which gives the first 'n' characters
of a$, and RIGHT$(a$,n) which gives the last 'n' characters.

To convert the case of a string you can use UCASE$(a$) which converts all
small letters in string to capitals, and LCASE$ which is the opposite.

Finally the function TRIM$ removes any spaces from the beginning and end of a
string, so TRIM$("  hello  ") gives "hello"

2.4.2 Bit Manipulation
----------------------

These functions are only needed by more experienced programmers.

You may have noticed that the AND,OR and XOR operators in FESBasic
are 'logical' not bitwise. The bitwise operations are available but
as functions. So to mask out bits except 0 and 1 of 'a' use
                a=AND(a,3)

Also direct bit manipulation functions are available:
    BSET(a,n)   sets bit n of a
    BCLR(a,n)   clears bit n of a
    BCHG(a,n)   toggles bit n of a
    BTST(a,n)   tests bit n of a

Note these are functions not statements, so write a=BCLR(a,0)
instead of BCLR a,0

Also note that NOT is a logical function. To do a bitwise negation use
something like XOR(n,-1)

2.4.3 Arithmetic
----------------

Various mathematical operations are available:-
    ABS n       the "absolute value" of n, ie n made positive
    MOD(a,b)    the remainder when 'a' is divided by 'b'
    -           negation
    INC n       n+1
    DEC n       n-1
    MULT(a,b)   a*b
    DIV(a,b)    a/b

The top three of these are standard BASIC, the last 4 are new to FES.

MULT and DIV are subtly different to the * and / operators. All work is
performed in 16 bits, with no error checking performed. Division by
zero gives int machine infinity, (ie 32767). Multiplication results are
modulo 65536, sign adjusted. If this does not mean much to you then you
will probably never need to use these functions.

INC and DEC can be useful in avoiding brackets sometimes, 3*INC a instead
of 3*(a+1). It is a matter of personal choice really. There is little
performance difference between either form.

2.4.4 Input/Output Functions
----------------------------

A range of functions are available to perform input and output operations:-

    INKEY         Key Press as ASCII code
    INKEY$        Key Press as string
    SHIFTKEY      Which Qualifier keys are pressed
    INPUT$(a)     Read 'a' characters from keyboard
    INPUT$(#n,a)  Read 'a' characters from a file.
    MOUSEB        Which Mouse Buttons are pressed
    MOUSEX        Mouse X position
    MOUSEY        Mouse Y position
    STICKB(n)     Joystick 'n's Fire Button
    STICKX(n)     Joystick 'n's Left/Right Position
    STICKY(n)     Joystick 'n's Up/Down Position

2.4.5 Format Conversion Functions
---------------------------------

It is often required to convert data from one format to another.

To convert an int or a long to a string of digits use STR$. To perform the
reverse operation, a string of digits to a long, use VAL.

To convert an int/long to an ASCII string use CHR$, the reverse can be
done with ASC.

Ints and Longs can be converted to 2 or 4 character strings respectively
by using MKI$ or MKL$. These are different from STR$ in that STR$
produces a string that makes sense to a human, eg STR$(84) is "84".
MKI$(84) is "_T". To convert back from the MK?$ format use CVI or CVL.

CVI and CVL can also be used to convert ints to longs or vice versa.
Although this is normally done automatically it is sometimes necessary to
do it explicitly. For example
  PRINT 3000*9000       gives an overflow error, as it multiplies two ints
                        to give an int, but the answer is too big for an
                        int to cope with, but
  PRINT 3000*CVL 9000   does work, as 9000 is now a long, so the result of
                        the multiplication is a long, which can cope with
                        the value 27000000. Note if, as in this case, you
                        are working with constants, you could use
  PRINT 3000*9000&      which is more succinct.

{When CVI or CVL are used like this it is jargon to refer to them as
 "cast" operators. That's a good one to impress your friends with your
 knowledge of computing}

2.5 User Defined Functions
==========================

FESBasic allows you to build up functions of your own. All User Defined
Functions must begin with the letters 'FN' followed by a name, the
rules for FN names are the same as for variable names, so valid
names are

    FNadd           FNSwap$         FNlong_var_name&

When it is used a user defined function must be followed by brackets. Even
if there are no augments the brackets must still be specified.

Functions are defined using DEF. The end of the function definition is
marked by a ENDDEF statement followed by an expression. This expression gives
the value returned by the function.

FES Basic does allow recursion. That is a function can be defined in terms
of itself. So the standard example; the Factorial:-

    'Factorial Program
    'Asks for a number then calculates its factorial
    '{ So if the user gives the number 5 the answer is 1x2x3x4x5 }

    INPUT "Give me a number ",a
    PRINT "Factorial of ";a;" is ";FNFactorial&(a)
    STOP

    DEF FNFactorial& n          'use & as numbers can be quite big
      ' Factorial calculated recursively.
      ' Factorial 1 =1;
      ' Factorial n = n* Factorial (n-1)

      IF n=1 THEN RETURN 1      'RETURN can be used to return value

    ENDDEF n*FNFactorial&(n-1)   'call FNFactorial again, and again...


Notice the slightly weird syntax for DEF. There are no brackets around
the list of augments. (It is the same for DEFPROC later). I'm not quite
sure why I programmed it that way, but that's the way things happened!

Function definitions can contain LOCAL variables, just like PROCedures.



**************************************************************************
==========================================================================
                            3 CONTROL CONSTRUCTS
==========================================================================
**************************************************************************

Probably the most important parts of computer programs are the statements
which control the flow of the programs. Performing calculations is fine
but if that is all that is required then the end-user is probably better
off with a pocket calculator. The main advantage of a computer is its
ability to perform operations many times, this looping constructs.

There are several Constructs that can be used in FES Basic to perform
branching and looping.

    Labels:...GOTO
    IF...[THEN]
    FOR...NEXT
    REPEAT...UNTIL
    WHILE...WEND
    DO...LOOP
    SELECT...CASE
    PROC

There is also the EXIT command which can be used to make an early exit from
a FOR...NEXT, DO...LOOP ,WHILE...WEND or REPEAT...UNTIL.

3.1 Labels:...GOTO
==================

These are the least preferred way to perform operations. This method is
very much frowned upon in professional programming circles, however it
possibly the one that beginners may find themselves most familiar with.

A Label is a method of marking a point in a program. In FESBasic this is
done by placing an Alphanumeric word at the beginning of a line followed
by a :.

The computer can be made to jump to a label at any point by the use of the
GOTO command. The word GOTO is followed by the label of the point to jump
to. There must not be a : after the label at the GOTO.

For example, the standard program that everyone writes:-

        Label:
        PRINT "FOZZ is ace!"
        GOTO Label

Care must be taken with GOTO's not to jump into or out of other control
constructs. If you do the behaviour is not defined. There may be an error
message, the program may work correctly on some computers but not on others,
etc. Sod's law states that in this last case then the only computer in the
cosmos that the program works on will be the programmers own when no-one
else is in the room.

Although the GOTO command is available it should only be used where absolutely
necessary. It is much preferred to use other constructs:-

        DO
          PRINT "FOZZ is ace!"
        LOOP

3.2 IF...[THEN]
===============

This is the main decision making construct. It can take two forms:-

    IF condition THEN statement

or  IF condition
      statement
      statement
      :
      :
    ENDIF

The first form is quicker to type, requires less lines, but can only cope
with one statement. The second form can cope with any number of statements,
even with more IF statements.

What forms a "condition"?

It can in fact be any expression that gives a numeric result. If the result
is not zero then it is regarded as "true",if zero then "false".

So we can say:-
    IF a<b THEN PRINT "a is less than b"
or  IF a=2 OR a=3 THEN PRINT "2 or 3"

{NOTE it is not possible to write
    IF a=2 OR 3 THEN PRINT "2 or 3"
 See section 2.3.3 for what this means! }

If we are using the longer IF construct then we can have several conditions,
these are of the form ELSEIF condition. This allows the use of multi-way
decisions:-

    IF a=1
        PRINT "MONO-"
    ELSEIF a=2
        PRINT "BI-"
    ELSE
        PRINT "MULTI-"
    ENDIF

There can be any number of ELSEIF clauses, and each block of statements can
contain any number of statements, but in all cases only one block will get
executed.

3.3 FOR...NEXT
==============

The FOR...NEXT construct is used to repeat a section of the program a given
number of times.

A variable is used as a counter, It is set to a value at the start of the
loop, then increased by a given value on each loop until it reaches another
given value.

    ' eg count from 1 to 10
    FOR k=1 TO 10
      PRINT k
    NEXT

If it is required to count down then either use STEP with a negative value
or FOR val=value DOWNTO value2.

3.4 REPEAT...UNTIL
==================

REPEAT...UNTIL does exactly that. The block of program between the REPEAT and
the UNTIL is executed repeatedly until a condition is satisfied.

    PRINT "Enter 0 to exit"
    REPEAT
      INPUT "Give me a number ";a
      PRINT a;" Squared is ";a*a
    UNTIL a=0

Note that when using REPEAT...UNTIL the block is executed at least once.

3.5 WHILE...WEND
================

This is the mirror of REPEAT...UNTIL. Unlike REPEAT the condition is placed
at the beginning of the block. The block is terminated with a WEND instruction.

This allows a block to be executed zero times if the condition fails the
first time round.

    PRINT "Exponential Tables :"
    INPUT "Give me a number ";a
    WHILE a<10000
      PRINT a
      a=a*a
    WEND

3.6 DO...LOOP
=============

This construct is a sort of combined WHILE/REPEAT. The loop repeats
continuously until an EXIT command is executed.

    PRINT "Enter 0 to stop"
    DO
      INPUT "Give me a number ",a
      EXIT a=0
      PRINT a;" squared is ";a*a
    LOOP
    PRINT "Finished"

3.7 EXIT
========

The Exit command can be used to leave a loop part of the way through. It is
the only way to leave a DO...LOOP, and can be used to exit from any of the
other three loops.

The simplest form of the command is

    EXIT type_of_loop

eg  EXIT
    EXIT FOR
    EXIT REPEAT
    EXIT WHILE

Exit on its own is to exit from a DO...LOOP.

In addition a condition may be placed after the "type", in this case the loop
will only exit if the condition is true.
NOTE this looks weird when used on a WHILE loop, eg
    EXIT WHILE a<3      means exit the loop if a is less than 3.


3.8 SELECT...CASE...
====================

This allows a multi-way decision.

After the SELECT comes an expression. The computer then searches through
the list of CASE's for a match. If one is found then the block after that
case is executed. The word REMAINDER can be used to catch any cases not
matched before.

    PRINT "Press:-"
    PRINT |"1.  Load"||"2. Save"||"3. Exit"
    INPUT ">",action

    SELECT action
    CASE 1
      INPUT "Load which File? ",FName$
      PROC LoadFile FName$
    CASE 2
      INPUT "Save which file? ",FName$
      PROC SaveFile FName$
    CASE 3
      STOP
    CASE REMAINDER
      PRINT "Invalid Option"
    END SELECT


3.9 PROCedures
==============

Procedures are the recommended way of splitting a program up into manageable
chunks. They allow blocks of program to be named, each block can have its own
'local' variables separate from all other blocks, and generally makes your
programs far better structured.

Unfortunately the syntax for PROCedures in FES Basic is highly non-standard.
I'm not sure how the syntax came about, but I'm stuck with it now. Its not to
bad once you get used to it.

Lets start of by looking at how to define a procedure. First comes the
statement DEFPROC then the procedure name (alpha numeric just like a variable)
then a space then any parameters it takes, all separated by commas.

eg      DEFPROC myproc a&,b,c$

Note that the variables used in a DEFPROC line are independent of any
variables that may have the same name in the rest of the program.

After the DEFPROC comes the program lines that make up the procedure, and
the whole thing is finished of with an ENDPROC.

So a full example:

        DEFPROC stars n_spaces,n_stars
          LOCAL k       'the variable 'k' is independent of any other 'k's

          FOR k=1 to n_spaces
            PRINT " ";
          NEXT

          FOR k=1 to n
            PRINT "*";
          NEXT
          PRINT
        ENDPROC

To run the procedure use the command PROC, followed by the name then the
values to give each parameter. So to display 5 spaces then 3 stars in the
above example use

        PROC stars 5,3

Either value could have been a variable or a complete expression.

See the example file "procs.fes" for a complete example.




****************************************************************************
============================================================================
                            4. STATEMENTS
============================================================================
****************************************************************************

A 'statement' is the word at the beginning of each line which describes what
that line is going to do. So PRINT,GOTO,IF,LINE,CLS,COLOR are all statements.

FESBasic currently contains about 65 statements (There is some confusion about
lines containing a comment only, or about assignment lines, but this is
all besides the point!).

For a full list of all the statements please refer to the FESBasic_HelpFile.
It consists off all the statements with descriptions.

In this section I will describe very briefly some of these statements by
subjects...

4.1 PROGRAM FLOW
================

There are quite a few statements which control the flow of execution around
a program. These are explained in more detail in section 3: Control Constructs

GOTO label      The most blatant. Causes a jump to a specified point.

GOSUB label     Causes a jump to the label. When a RETURN statement is
RETURN          encountered the program jumps back to the line after the
                GOSUB.

PROC            This causes a jump to be made to a given location, like GOSUB
DEFPROC         however PROC allows passing of parameters, and provides
ENDPROC         clearly defined limits to blocks of program.

FOR             This is used to repeat a number of lines a set number of
NEXT            times. Use this construct when you can determine the number
                of times round the loop before you start.

REPEAT          This is used to repeat a block of program several times until
UNTIL           a given condition is met. The block will always be executed
                at least once.

WHILE           Similar to REPEAT...UNTIL but the condition is at the start
WEND            of the block. This means that if the condition fails on the
                first time round then no code will be executed.

DO              Repeats a block of code indefinatly until an EXIT statement
LOOP

EXIT            Leave a looping construct

IF              Allows decision making, a block of code can be executed only
ELSEIF          if certain conditions are met.
ELSE
ENDIF

SELECT          A more compact form of IF...ELSEIF...ELSEIF...ENDIF when the
CASE            conditions are all very similar.
ENDSELECT


4.2 INPUT AND OUTPUT
====================

PRINT           Displays the values of zero or more expressions on the screen.
                Expressions can be separated by semi-colons in which case they
                will be displayed side by side on the screen, by commas when
                they will be displayed in separate columns or by bars '|'
                when they will appear on separate lines.

INPUT           Displays a prompt then accepts information from the user and
                places it in a variable.

OPEN            Opens a channel to a (disk) file. Information can be sent to
                the channel using PRINT # or WRITE #. Information can be read
                using INPUT #,  INPUT$(#n) or READ #.

CLOSE           Closes a channel opened by OPEN.

PRINT #n,       Similar to PRINT but writes the output to channel 'n'

WRITE #n,       Writes values to channel 'n' in a computer readable format.
                This format is understood by READ #

INPUT #n,       Similar to INPUT but reads from a file not the keyboard.

READ #n,        Retrieves information from a file written to by WRITE #n.

BWRITE          Writes a block of memory to a channel opened with OPEN.
BREAD           Reads a block of memory from a channel.


4.3 GRAPHICS
============

SCREEN 1,w,h,n  Determines the screen mode that Basic will use. Note the
                slightly strange syntax with a 1, at the beginning!

COLOR f,b,m     Chooses the colour to draw in.

PALETTE         Changes the selection of colours available

LINE            Draws straight lines on the screen.

BOX             Draws hollow or filled boxes.

CIRCLE          Draws filled/hollow circles/ellipses.

AREA            Fills an arbitrary shape with up to 20 vertices.
AREAFILL

FLOOD           Fills a shape already drawn on screen.

PSET            Sets a pixel on the screen.

GET             Copy a section of screen to a buffer

PUT             Copy a buffer onto the screen.

SCROLL          Move a part of the screen around.


***************************************************************************
===========================================================================
                        5. FINAL POINTS
===========================================================================
***************************************************************************

This chapter is intended mainly for persons already familiar with other
versions of BASIC. In it I list the peculiarities of my language in
comparison with others.

5.1 Integers Only
=================

The freely distributable version of FESBasic is limited to working only
with Integer Numbers (ie numbers with no decimal points). To obtain a
version that supports real-numbers you need to register (see the
accompanying file Register.doc)

This limitation means that for example 5/3 is, as far as the  computer is
concerned, equal to 1, as 1 is the largest number of times that 3 can go
into 5.

5.2 Syntax for PROCs and DEF FNs
================================

Procedures are defined by using the command DEFPROC followed by the proc
name and then any augments, without brackets around the list of
augments. Variables local to a procedure are declared by using the
statement 'LOCAL' on the line immediately after the DEFPROC.

To call a procedure the word PROC must be used, and again there are no
brackets around the augment list.

So for example

        PROC Stars n
        .
        .
        .

        DEFPROC Stars number
          LOCAL k
           .
           .
           .
        ENDPROC

To define a function the syntax is exactly the same as for a procedure
except use the word DEF not DEFPROC. Again there are no brackets around
the augment list.

User defined function names must begin with the letters FN followed by at
least one alphanumeric character. The return type of a function is placed
at the end of the name, so FNx returns an integer, but FNy$ returns
a string.

When calling a user defined function however the brackets are essential,
even if there are no parameters.

The return value expression is placed after the ENDDEF that finishes the
definition. Early exit from a function is possible using RETURN value but
note that it is illegal to exit from within a loop. The function below
will have undefined effects:-

        DEF FNFindValue value

          FOR k=1 to 10
            IF a(k)=value THEN RETURN k
          NEXT

        ENDDEF 0

Some other BASICs do allow this sort of early exiting from definitions, but
FES does not. Using this type of construct can get the computer VERY confused!

You may use the RETURN statement within block IF and SELECT constructs however,
but not if the IF/SELECT is within a FOR/DO/WHILE/WEND etc.

eg      'This is OK
        DEF FNFindValue Value

          SELECT Value
          CASE 1,2,3
            RETURN 1
          CASE 4,5,6
            IF RND(3)>2
              RETURN 2
            ELSE
              RETURN 4
            ENDIF
          CASE REMAINDER
            RETURN 0
          ENDSELECT
        ENDDEF

5.3 LOGICAL AND BITWIZE OPERATIONS
==================================

The operators AND OR and XOR in FESBasic are logical operators. That is they
give the value '1' if the answer is true and '0' for false based on the whole
number input, not on each individual bit input.

This means that     a=5 AND 4   gives a=1 not 4 as some BASICs might.

The Bitwize operations are available as functions though:-

So you would write  a=AND(5,4)  to get a=4.

Also the operators AND and OR can be used on Strings:-

        a$ AND a        gives   a$ if a<>0
                                "" if a=0

        a$ OR b$        gives   a$ if a$<>""
                                b$ if a$=""

These functions are not often used but can be quite useful, for example to
set a default value on a string:

other BASIC     INPUT "Enter your name ",name$
                IF name$="" then name$="Anon"
                :
                :

FES BASIC       Input "Enter your name ",name$
                name$=name$ OR "Anon"

or to handle plurals

other Basic     PRINT n;" apple";
                IF n<>1 THEN PRINT "s";

FESBasic        PRINT n;" apple";"s" AND (n<>1);


5.4 PRINT USING and FORMAT$
===========================

FESBasic does NOT support the PRINT USING syntax found on many other versions
of BASIC. Instead the C-Style function FORMAT$ is used.

FORMAT$ can be used in any context unlike USING which could only be used in
conjunction with PRINT.

eg      'print a persons name and age
        PRINT FROMAT$("Name: %15s  Age %2d",name$,age)

        would give something like:-

        Name:     Simon Forey  Age 20

5.5 STAND ALONE PROGRAMS
========================

If you have written a program using FESBasic it is not neccary to load it
into the editor every time you want to run it.

If you create a program with an Icon then the program can be run by
double-clicking its icon. Just make sure that the program "basic" is on
your disk in the same place as the "Tool Type" of the Icon says it is.

Running programs from the CLI is equally easy. Just make sure that "basic" is
in your command path ( eg put it in the 'c' directory of your disk) then
type        basic file_name.fes

NOTE: For a program to be executable like this it must have been saved using
SAVE or SAVE PROT from the editor. Programs saved using SAVE ASCII cannot be
run without loading them back into the editor.

So suppose you have written a game called "game.fes" and you want to make a
bootable disk that will boot to the game. You need the following disk
structure

        c
           basic
           «any other commands used»
        s
           startup-sequence
        libs
           reqtools.library     OR   } only if you use the FILEREQ$ function
           asl.library               }
        game.fes

the startup-sequence would look something like

        «any commands you want to run before game»
        basic game.fes
        «any commands for after game»