Planet Lander

ZX Computing

Graham Charlton

HEWSON'S HINTS AND TIPS Hewson Consultants have a variety of ZX81 products - including games software, 'serious' software and Andrew Hewson's book 'Hints and Tips for the ZX81'. Graham Charlton puts them through their paces for ZX Computing. A big bundle of material from Hewson arrived at my home, and I spent a long weekend working through it. The products I looked at, and their prices, were the book 'Hints and Tips for the ZX81' (£4.25), Space Intruders (£5.95), Language Dictionary (£3.75) and Planet Lander (£3.75). The area covered by the hints and tips book is shown clearly by the chapter titles: Saving Space; Understanding the Display File; Converting ZX80 Programs; Chaining Programs; Machine Code; plus a mixed bag of twelve 1K programs. The book appears to be aimed mainly at those with only 1K RAM. If you have only 1K, I'm sure you realise how difficult it is to run even the smallest of programs. Therefore it is essential to understand how your ZX81 works, and know some short cuts to help you in programming. This book should help you. 'Hints and Tips' contains an extensive 27-page chapter on machine code, although it doesn't give a full list of codes. Hewson Consultants do supply, for £1.45, a full list, in which each Op Code is explained and cross-referenced. The book eases the user into the idea of using machine code, with many examples of its use in the book. As well as this, I found the chapter on chaining programs quite enlightening. I didn't know, until I read it here, that it was possible to pass data between programs. In all, this slim volume is good value, and an essential aid to those with an unexpanded ZX81. SPACE INTRUDERS This program, for a ZX81 with 16K, comes dubbed once on each side of a cassette, along with full instructions. Even if you'd never used a ZX81 before you got this program, the instructions would enable you to load and use the computer. Written in machine code for fast action, the program has 40 alien ships in each squadron, three laser guns and full score display. As well as this, the ZX81 can play itself - although not very successfully. Continuous firing is available, and you have to be quite quick to avoid the aliens' bombs. All in all, this is an enjoyable version of the popular arcade game. LANGUAGE DICTIONARY Written for a ZX81 with 16K, Language Dictionary is an easy-to-use program, with a number of options. It can search for a word in either of the languages used, allows you to update or dump the entire contents or to save these on cassette. Although the method used to store the words packs them tightly it appears it would take a long time to find a word stored near the end when the dictionary was full. STATISTICS This pack consists of three 1K programs - Graph Plot, which does exactly as the title suggests, using data entered from the keyboard; Chi Squared Test, which "calculates the value of the chi squared statistics for comparing observed and expected values"; and Statistics, Regression, Trend which is used to calculate mean and standard deviation and a least squares regression line or trend line. I am sorry to say that these programs appear to do little more than someone with a pocket calculator and a piece of graph paper could achieve - and probably in less time than it takes to locate and load the required program. Of course, it would be valuable if a large number of similar problems had to be worked through. At the very least, the programs prove convincingly that the ZX81 can be used for more than games. Perhaps a 16K maths tape would be more useful, and would provide a better indicator of the ZX81's abilities. PLANET LANDER This tape contains four 1K programs. In Planet Lander you have to (yawn) land your spacecraft on a planet's surface. Stopwatch is self-explanatory. The third program is Space Docking, in which (yawn again) you have to dock your spacecraft with the space station. The final program is Clock, in which you set the time and then sit back and watch the display increments each five seconds. Two of these programs are available from the book Hints and Tips' so I suggest you buy the book. You'll learn a fair amount, and enjoy using the book far more than you will this last pack.