First Book of Party Tricks for the ZX81 (1K)

ZX Computing

Alex Heywood

CARING FOR YOUR COMPUTER Reviewer Alex Heywood takes a selection of books from ZX and computer library shelves and assesses their value for owners of Sinclair Computers. Published by Video Software Ltd., this slim (26 pages) volume should not be sneered at because of its unimpressive size or presentation. The programs are, on the whole, original in concept and implementation, and are documented in great detail, which helps a lot in trying to work out what part of a program does what. The programs are: Shoot; Sketch; Name the Day; Train; Onger-Wonger; Weather; UFO; Who Shot JR; Field Gun; and Follow Hat. Ignoring the less original ones, with titles such as 'Sketch', I decided to have a look at the ones which showed a truly creative approach to the problem of squeezing a program into 1K. In SHOOT, you are about to take a penalty, and the goalkeeper is waiting for you. Press any key to shoot and the goalkeeping attempts to save your shot. A running total of your goals and his saves is kept by the ZX81. The most interesting thing about this program (apart from the fact that you'd need to be told what each symbol represents, which is neither surprising nor important) is a line which saves a considerable amount of space by using the method the ZX81 works out logical expressions. The line, 350, reads: LET J = A -(S A OR S = T OR S (B + B)), which changes the value of the A which is assigned to J only if one or more of the conditions within the brackets are true. TRAIN produces a little train which obeys the "5" (move left) and "8" (move right) keys. Fun to watch, but that's about all. The program which follows it in the book, Onger-Wonger, shows how to make the computer draw its own pictures. In this case, it draws an Onger-Wonger bird which flies around the screen in ever-decreasing circles. Once you've run that, you can use the program for storing your own pictures as a line of 'data' as elements in a string. The computer accesses the string element by element, and as a result of what it finds in the string, draws the picture. This program would usefully serve as a subroutine in a much larger program to set up the starting scene. First Book of Party Tricks for the ZX81 (1K), Philip Smith, Video Software, no ISBN.