Structure-In-BASIC                                          -*-org-*-

A technique for writing structured programs in Minimal BASIC.

Structure-In-BASIC (SIB) is intended for beginning programmers who
have been introduced to Minimal BASIC and wish to create more complex
programs (programs too long to display on a single screen without
paging/scrolling) before learning another language with better
support for structured programming, or for advanced programmers who
wish to create structured programs in BASIC.

SIB is composed of a set of source code patterns for implementing
standard program structures in BASIC. The patterns should be simple
to insert into program source, easily recognizable and distinctive,
and undamageable by line renumbering. They should also assume no
knowledge of other programming languages on the part of the
programmer.

* Sequence

A sequence block is simply a series of consecutively-numberes program
statements. REM statements (no standard format) should be used to
describe the entire block or subsections as needed. Statements that
are the target of branch commands (GOTO, etc.) must be descriptive
REMs.

* Selection

** Conditional

<pre>
01000 REM /// BEGIN CONDITIONAL \\\_________________________
01010 IF skip-condition THEN 1030
01020 REM conditional sequence ...
01030 REM \\\ END CONDITIONAL ///---------------------------
</pre>

** Alternative

<pre>
01000 REM /// BEGIN A
</pre>

* Repetition

** FOR-NEXT Loop

(Use standard BASIC syntax.)

** LEAVE-OR-LOOP Loop

<pre>
01000 REM /// BEGIN TEST-EXIT \\\___________________________
01010 IF exit-test THEN 1040
01020 REM loop sequence ...
01030 GOTO 1000
01040 REM \\\ END   TEST-EXIT-LOOP ///----------------------
</pre>

** LOOP-AND-REPEAT Loop

* Compound conditionals

DEC BASIC-10 doesn't include logical operators AND, OR, or
NOT. Although equivalent functions can be defined (see UTILFUN.BAS),
the following patterns can also be used.

** AND

Execute sequence Sp if all predicates p1 ... pn are true.

100 IF !p1 THEN 130
110 IF !p2 THEN 130
...
120 IF !pn THEN
120 REM sequence Sp ...
130 REM end structure ...

** OR

100 IF p THEN 120
110 IF !q THEN 130
120 REM p OR q processing ...
130 REM end structure ...

** Negation

In the AND and OR structures, boolean negation is achieved with the
opposite relational operator:

|---+----|
| = | <> |
| < | >= |
| > | <= |
|---+----|