Re: My first program
Some tricks for shop computers I used to employ were:
1) A POKE to the VIC-20 video chip to change the screen width from 22 columns to 23 or 21. This would cause anything on the subsequent lines to be offset left or right by one extra character each line. Really annoying for the shop assistants who couldn't figure out why their program listings were going diagonally down the screen.
2) Running a simple loop to copy the CBM-64 ROM into the underlying RAM, a POKE or two to keep it there, then a few more POKEs to change the SYNTAX ERROR text (now in RAM) to something far less pleasant. Then I'd stand back to watch kids (usually) cause an error and ask their unsuspecting parent what that meant!
3) Enter a short program into a Spectrum that changed the screen to 2 shades of blue, print "COMMODORE 64 BASIC V2", "64K RAM SYSTEM 38911 BYTES FREE" and "READY" with a loop to flash a cursor. That got lots of people confused! I once even convinced someone that a Spectrum had had a CBM-64 ROM installed in it by mistake!