Modifications Or Corrections To Previous Articles
Atari owners who use OSS DOS 2.20 from Optimized Systems Software must first select Q from the DOS menu to quit to DOS XL, then select T to go to cartridge before attempting to load this game from the December 1984 issue (p. 99).
Due to a printing error in line 2030 of this game from the February 1985 issue (p. 60), the STRIG function to read the joystick button appears as STPIG. Also, lines 20115, 23500, and 27035 are too long to type in as listed. To enter these lines, simply omit all spaces between BASIC statements and variables. For example, POKE BC,14 can be typed as POKEBC,14.
Machine Language Multiplication
In Part 2 of the series on multiplication in the "Machine Language" column (p. 121, February 1985 issue), the high and low bytes of the product are switched in the example program. The last few instructions of the example should read as follows:
Thanks to Karl Schmitt, Norman Sprock, and other readers who wrote in with the correction.
IBM Illegal Function Errors
A number of readers have reported problems with illegal function call errors in COMPUTE!'s graphics games for the IBM, such as "Horse Racing" (October 1984) and "Paratrooper" (January 1985). If you receive an Illegal Function Call error message in a line containing a PUT statement (such as line 1220 of Paratrooper), it most likely means that you have made a typing error in the DATA statements that define the graphics displayed by the PUT. When you see that error message in a line involving PUT, check all your DATA items carefully.
Proofreading The IBM Proofreader
Many readers have had problems getting the "IBM Automatic Proofreader" to work properly. The program is correct as listed, but if it's not typed in correctly, you may receive the cryptic message Error #2. The Proofreader traps all errors, even syntax errors. Instead of getting the usual "Syntax error in ..." message, you get the error number (2 is syntax error) with no hint as to where the error might be. To help you find your typos, change the 650 in line 140 to 0. This turns off the error trapping so you'll get the usual error messages if you have any errors.
Before using the Proofreader to type in programs, it's a good idea to test all the Proofreader commands, especially the SAVE command, just to make sure there are no bugs lurking in some obscure place in the program. To test the Proofreader's SAVE command, run the Proofreader and type in one line, say 10 REM. Now save this test program. If you didn't get an error message, you can safely type in a complete listing without fear of losing all your typing due to a bug in the SAVE command. When you think you have all the bugs out, type BASIC to exit the Proofreader, change line 140 back to normal, and save this bug-free version of the Proofreader.