SB BBC @ GBR
Oldie hints/tips #058-063 (rep.)
Hints and tips from the archives of Wakefield BBC Micro User Group...

58. While...do structure
    ~~~~~~~~~~~~~~~~~~~~
You may have missed the presence of a WHILE-DO or WHILE-ENDWHILE in BBC Basic
(it's in version5 as per the Arc). Eg.

   WHILE X%<100 DO X%=X%+1:A%=A%*B%
or
   WHILE X%<100:X%=X%+1:A%=A%*B%:ENDWHILE (as on BBC BASIC V)

REPEAT-UNTIL and FOR-NEXT loops have a disadvantage compared to WHILE-DO or
WHILE-ENDWHILE loops in that they always execute at least once, whether they
need to or not. In the examples above, the loop would not execute at all if
X% was >=100.

Well, you can imitate WHILE-DO or WHILE-ENDWHILE with the following:

  REPEAT IF X%<100 THEN X%=X%+1:A%=A%*B%:UNTIL FALSE ELSE UNTIL TRUE

It may not look very elegant, but it avoids GOTOs, so that makes it
structured in my book! (Source ... Beebug).

59. Variable names
    ~~~~~~~~~~~~~~
When people start programming in Basic, there is a tendency for them to
stick to variable names like A$, B%, FRED etc.. This has three drawbacks.
First, it is not very easy to pick out variables from keywords like FOR,
TO, PRINT etc., as everything is in capitals. Second, it is easy to
accidentally use a reserved word as part of a variable; TODAY is the
classic mistake, as it starts with TO. Third, when you return to the
program after a few days or weeks break, you will find it hard to remember
just what A$ meant. The solution is to use lower-case variables whenever
possible, and use long, meaningful variable names like "name$", "year%",
"degrees" etc.. If you are really pushed for memory space, then using the
single-letter integer variables A% to Z% can help, as can shorter variable
names such as "nd$" instead of "newdate$", but by and large you will not
need to resort to that.

60. Opening disc files
    ~~~~~~~~~~~~~~~~~~
When you open files on a disc for input, using the commands OPENIN or OPENUP,
the syntax is basically chan=OPENIN("myfile"). The first file to be opened is
allocated a channel number like 1, (ie. the variable 'chan' becomes 1), and
if you open another file without closing the first, it is allocated the next
channel number, (eg 2), and so on. The numbers don't necessarily start at 1;
that's just an example.

On most DFSs and ADFS, an interesting thing happens when using OPENIN or
OPENUP, where the filename should already exist on disc, but cannot be found,
either because you have put the wrong disc in, or maybe because you have
mistyped the filename. Instead of causing an error, as you might expect, it
simply allocates channel number zero. Thus, you have a very useful way of
trapping the mistake before it actually causes an error. Eg. you could add
something like:

 IF chan=0 THEN PRINT "Oops!":GOTO 200

There is no need to use CLOSE#, as the file hasn't been opened in the first
place. Only when you attempt to use INPUT#/PRINT#/BGET#/BPUT# on this
non-existent file, does the DFS return the error "Channel", (ERR=222).

61. Restore statement
    ~~~~~~~~~~~~~~~~~
It is wise always to use the full RESTORE (+ line number) syntax in programs
containing DATA statements, even if they theoretically don't need them. If
you don't, then rather strange things can happen if you change screen Mode in
between reading DATA statements. This is because the Basic stack is stored
immediately below HIMEM, and is therefore lost when you change Mode. For the
same reason, you must not use MODE or CLEAR within Functions and Procedures,
as the program will 'forget' where it has come from! Using MODE will give an
error message, but using CLEAR will not, and it can cause all sorts of
infuriating and unpredictable errors!

62. Abbreviations
    ~~~~~~~~~~~~~
You can replace PRINT:PRINT:PRINT with PRINT'' . In fact, an apostrophe will
force a new line at any time; try typing PRINT"HELLO"'"FRED" and see what
happens. (See User Guide, bottom of page 324.) You can also replace
NEXT A:NEXT B:NEXT C with NEXT A,B,C and NEXT:NEXT:NEXT with NEXT,, .

63. Underlining in Wordwise
    ~~~~~~~~~~~~~~~~~~~~~~~
Owners of many types of printer may experience problems when centering
underlined text in WORDWISE. The underlining tends to extend all the way to
the left margin, instead of starting at the beginning of the heading. This
effect also be seen if you are using the 'ds' and 'de' codes in Wordwise
Plus, and are previewing in 80 column mode. The cure for this is to insert
one space after the centering code, but before the underline code. If exact
centering is vital, then an additional space after the final white control
code would "balance" the first space. Better still, use the pad character,
("|" by default), instead of a space, so that it is clearly visible in Edit
Mode. The {G} and {W} represent the green and white control codes
respectively, and the printer codes used are for Epson-type printers. (You
can substitute 'ds' and 'de' if you have Wordwise-Plus.)

 Before: {G}ce{G}oc27,45,1{W}THIS IS A HEADING{G}oc27,45,0{W}
 After : {G}ce{W}|{G}oc27,45,1{W}THIS IS A HEADING{G}oc27,45,0{W}|

                 ^           pad character or space              ^

73 Rick G4BLT @ GB7WRG