PRESENT

Author: regregex
Category: Christmas Challenge
System: BBC Micro A/B/Master, Acorn Electron
Language: BBC BASIC
Len source code: 110 bytes
Len exe file:     87 bytes
Len code only:    87 bytes
Instructions:
  Install and open BeebEm ( http://www.mkw.me.uk/beebem/ ).
  Click File -> Disc Options -> New Disc 0, enter present.ssd
  Click Edit -> Import Files to Disc -> Disc 0, select present.inf
  At the BASIC prompt, type CHAIN"PRESENT" and press RETURN.

  To reproduce the screenshots:
  Click Hardware -> BBC Model -> BBC Master 128
  Enter the following:
  *INSERT 9
  *CONFIGURE FILE 9
  *CONFIGURE MODE 4
  Press Ctrl+F12 (CTRL+BREAK), releasing Ctrl last.
  Then follow the instructions above.

Description: The program runs under BBC BASIC version 1 and up.
First it selects display MODE 4, an ASCII mode with square pixels that
has the backslash character; this automatically clears the screen and
places the cursor at the top left.  It positions the cursor with six
newlines and 19 spaces, then prints the bow on the centreline and leaves
the cursor to its right.

For each of the nineteen rows of the box, the program prints a newline
followed by eleven spaces to move the cursor towards the centre.  Then
the nineteen characters of each row are printed, each selected from a
four-character string according to whether the X and/or Y co-ordinates
are non-zero, modulo 9.  (SGN is the most efficient way to decide as the
inequality operators are non-associative and return a negative integer
when true.)  256 spaces are printed inside the box to align the ribbon
and right edge vertically.  Finally it waits for a keypress, then exits.

Comments:
Suitable for an SBC running BASIC if the MODE 4 statement is removed.
GET returns a number (the ASCII code of the key pressed) which IF,
having no THEN or ELSE clause, discards.