Z*Magazine: 22-Feb-88 #94From: Atari SIG (xx004@cleveland.Freenet.Edu)
Date: 07/24/93-09:21:40 AM Z
- Next message by date: Atari SIG: "Z*Magazine: 29-Feb-88 #95"
- Previous message by date: Atari SIG: "Z*Magazine: 15-Feb-88 #93"
- Return to Index: Sort by: [ date ] [ author ] [ thread ] [ subject ]
From: xx004@cleveland.Freenet.Edu (Atari SIG) Subject: Z*Magazine: 22-Feb-88 #94 Date: Sat Jul 24 09:21:40 1993 ______________________________________ |////////////////////////////////////| |////////////////////////////////////| |/SYNDICATE ZMAGAZINE 94 ONLINE NEWS/| |/----------------------------------/| |/PUBLISHER/EDITOR|February 22, 1988/| |/ RON KOVACS | Issue #94 /| |////////////////////////////////////| |////////////////////////////////////| |____________________________________| |Syndicate Publications | |Post Office Box 74 | |Middlesex, New Jersey 08846-0074 | |____________________________________| |Syndicate-ZMAG (201) 968-8148 3/12 | |XBN-ZMAG (617) 770-0197 3/12+| |Stairway-ZMAG (216) 784-0574 3/12 | |____________________________________| |///////////[-CONTENTS-]\\\\\\\\\\\\\| |____________________________________| |*|ZMag Newswire [Atari News Update]| |*|ZMag Technique [Mr. Goodprobe] | |*|Quick Mod [1200XL Keyboard] | |*|ST KeyLock [Lock up Mod] | |*|AtariWriter Plus and SpartaDos | |*|ZMag Archives [From GEnie Atari8]| |*|Basic Programming Part 7 | |_|__________________________________| ______________________________________ |*|Editors Desk ______________________________________ by Ron Kovacs Well, another week has slipped by and still no due date on the continuing saga of Kovacs Baby #2. Doctor said this past Saturday that he MIGHT have made a mistake and reset the day two weeks ahead! Details as they become available. In last weeks ZMag, (#93) I listed the Stariway to Heaven BBS number very wrong!! It turned out to be a voice line!! I corrected it above. My apologies to the party... The Syndicate BBS has returned to service. Returning this past weekend, with FoReM XE and a bare bones system. I will be updating it in the next few days. If you get a chance, Please call and atleast get your access back so when we are all together, you can get right into things. The number is: (201) 968-8148 300/1200 Ascii/Atascii. I want to thank Terry at Gateway City BBS for his assistance with the software. Give him a call at (314) 647-3290. Mike Shoenbach of the CompuServe Atari SIGS mentioned in the CO Sunday night that there will be a new area debuting on the SIG this week. Give it a call this week for details. I will update you on this next week. Interesting reading... John Nagy has alot to say this month in Computer Shopper. Please buy it or subscribe if you dont get it!! Newsletter info begins next week. Thanks for reading and hope to see on the Syndicate BBS! ______________________________________ |*|ZMag Newswire ______________________________________ Atari Update ============ Kyodo reported late last week that Atari has aquired court injunctions against six companies for infringing it's copyrights and patents. In the court injunction, agents of Atari seizd over $64,000 worth of pirated goods. Kyodo, a Japanese News Service reported "The six companies were alleged to have brought in Taiwanese copies of the Atari 200 video games and software game cartridges." Apple Computer took the same legal action earlier in conjunction with a new copyright law in Singapore. Kyodo is part of NewsNet which can be accessed through Compuserve and the IQuest area. IQuest reviewed in 1986 in ZMagazine. ______________________________________ ZMag Technique ______________________________________ A Review of... "Your Atari 8 Bit Comes Alive" by Mr. Goodprobe Your faithful hardware addict had the privilege of hearing the following short story recently: The fruit pickers down in good ole Florida decided to employ the services of some newfangled computerized robots to help them in the often tedious chore of picking scrumptious Florida oranges from the tress in which they are perched. But...an unforseen problem caused the project to grind to a screeching halt! It seems that in a cost cutting measure these "programmable pea-pickers" as I call em, were equipped with black and white video scanners. Needless to say, to a robot with a black and white scanner for video purposes, somehow a bright shiny orange ready for the pickin' and fluffy clouds bear a remarkable similarity! Thus on numerous occasions the robots were found "locked up" with their robotic arms waving towards the heavens in a futile attempt to pluck "cumulus" oranges from the sky! My oh my, what a sight that must have been. Anyone even remotely involved in the computer industry today cannot help but be excited and enthralled with the advent of so many new and exciting advancements in hardware design and development, and software versatility. Faster and more powerful are the keywords of today's computer revolution. But it is this very same computer revolution that is causing consternation in the hearts of many computer owners as they begin to feel left out by all the progress that is going on round about them. The very same computers which they hold near to their hearts (and had placed a severe load on their wallets in the past), are now "slow ancestors" to the "miracle micro's" of today. The news we see today is that these computers, like the Atari 8 bit series, will soon be a forgotten, but pleasant memory. Atari has made it known, that with the exception of the XE game system, this is the last year for their support of the 8 bit line. And Commodore too expects to sell its 8 bit line of computers only 2 more years, and hopes to push its Amiga into the forefront, and indeed it already accounts for 40% of its sales in the last few months. But, I wish to go on record by firmly stating that I do not feel these computer manufacturers are in tune with the facts as the presently exist. As in the case of the Atari 8 bit series, this user base contains some of the most knowledgable programmers, hardware enthusiasts, and general computer addicts known on this fine planet of ours. New applications, hardware, and ideas will continue to flow forth that will continue to keep these computers alive and well for all computerdom to see. One such item is a new disk/book combination called your "Your Atari 8 Bit Comes Alive", written by Richard Leinekecker, and edited by David Leinecker. These are the same fine folk that previously released "Your St Comes Alive" and "The Scientific ST". These previous 2 volumes were reviewed by me in earlier issues of Zmag, and all are available from Midtown Tv (see bottom of this article) and from selected software stores across this fine land of ours. Like its predecessors, it is chock- full of hardware projects that the user can build and run from his own computer. An accompanying disk is filled to the brim with programs that are used to run the projects you build. The programs are admittedly bare-bones as described by the author, and this is to encourage enhancement by the users themselves. Although they are in this fashion, they do the job well, and are the proud product of careful planning and many hours of debugging and enhancing. The first 3 chapters of this volume break the necessary ground you need to cover in order to understand these pertinent topics: 1.> The use of breadboards, and the etching of PC-boards to be used in the construction of these and other hardware projects. 2.> Construction of a 1.2 to 37 volt power supply for use with these projects and others you care to build in the future. 3.> The basics behind resistors, capacitors, diodes, transistors, IC's, and voltage regulators. 4.> A quick run-through of the binary number system, and hexidecimal operations. 5.> Programming tips that touch on: a.] Hardware specific peeks and pokes... b.] Graphics modes... c.] Useful memory locations... d.] Machine language routines from Basic... e.] Display lists... f.] Overlays... g.] Display list interrupts... h.] Vertical Blank interrupts... After breaking you in gently by guiding the user through the construction of 2 relatively simple projects using the joystick ports (reading data from them), and switch projects (like a computerized stopwatch), he then proceeds to unleash a barrage of fantastic hardware based goodies! Feast your eyes on these!: 1.> Door alarms (could even have 255 of them operational at the same time!) 2.> Visible light detectors 3.> Infrared light detectors 4.> Touch switches 5.> Speed detectors 6.> Frequency detectors 7.> Data encoders (as in encoded keypads) 8.> Light pens 9.> External device control A.> Data decoders B.> Serial data (teaches you how to build an infrared system capable of sending serial data via infrared light!!!). This project alone was worth the price of the book. C.> Data selectors D.> Analog data devices E.> Audio synthesizers F.> Tone decoders G.> Networking devices H.> Display lighting With the facts you will pick up from this fine volume, and the fun you will have building the projects contained within, you may finally be able to convince your wife that this computer you bought really was for "educational" purposes.....Nah!!!! "Your Atari 8 Bit Comes Alive" "Your ST Comes Alive" "The Scientific ST" are all written by and the exclusive property of Richard Leinecker. Keep those Atari's hummin! Mr.Goodprobe (on lend from) Midtown TV 27 Midway Plaza Tallmadge, Oh 44278 Atari 8/16 Repair/Sales Also:Commodore 8/16 Repair Many items have flat repair rate, call for prices! Zmag Midwest Headquaters bbs is: Stairway To Heaven 216-784-0574 300/1200 24 hours Featuring Zmag, 25 on-line games and Public Domain downloads for Atari 8 bit, ST, and Amiga computers! ______________________________________ Quick Mod ______________________________________ Captured from CompuServe Atari 8 To modify a 1200XL keyboard to work on other models of Atari computers remove the 15 conductor cable, ic chips, capacitors and resistors from the board and connect wires from the 22pin keyboard connector in the computer to the locations shown in the following diagram. I have done this modification to a 400 and think it will work with all models. I believe that the programmable function keys should operate properly on XL/XE computers but the OS in the 400/800 does not recognise them. 2 8 10 14 1+ + + + + + + +8 1+ + + + + + + +8 3 5 11 13 1 7 15 17 16+ + + + + + + 16+ + + + + + + + 4 6 12 16 19 21 15+ + + + + + + + + + + + + + +1 22 20 18 9 15 pin connector/left ic pad/right ic pad ______________________________________ Lock and Key for the ST ______________________________________ By R. Flashman [the Flash] Reprinted from Nybbles & Bytes, 9/87 I was walking by Radio Shack today, and in I went. Under the alarm section, I saw they sell a round key lock like the ones used on an IBM AT. Since it is for an alarm, it has the contact on one side, all read for an electrical wire. Hmmm, I thought. I am always getting annoyed by people who play with my ST at a show or meeting when I am busy doing something else... I bought it... And I found space right over my joystick ports (520) on top of the RF shielding, and now I have an AT style lock and key on my ST! Looks very good, was dead cheap, and in the off position, you cannot turn on the ST! Actually, so simple it is disgusting. (Lock cost $9.99) I haven't tried a 1040 yet, so not sure about location. I found two locations on the 520; on top of the unit, t othe back and left, directly above the cartridge port. Turn your 520 upside down and you will see how much space there is. I am hoping that the 1040 has the same space. The other, which is the one I used, is right above the second joystick port. (The one you DON'T plug the mouse into.) There is enought space, and it lies right above the RF shielding, it is also next to the power supply, so not much cable is needed. The switch has two connectors on its end. I connected two wires to it, and then opened up the RF shielding. You will notice that the power switch has three legs coming out of it. The one you want to get is the smallest one. (This is the one closest to the back of the ST.) I cut it right where it meets the main board. (Now that took guts!) Then I soldered one of my wires to it. I then connected the other wire to one of the wires that comes up from the board to that funny round magnet that is to the left of the power switch (and about an inch into the board). The wire that it gets wired to is the one closest to the mouse port. If you don't believe me, look under the board and you will see that originally that wire was connected to the leg that we just cut off the power switch. You NOW have a switch to the power switch. Turn the key off and the power switch becomes useless. This will void your warranty. But it works like a beauty. WE are now offering it as an option for our STs at the store! ______________________________________ Atariwriter + and SpartaDos ______________________________________ by Glenn K. Smith (70357,1136) This documentation covers how to make ATARIWRITER+ use the ramdisk of a 256k computer. You must have a Newell, Rambo or some other memory upgrade that gives you at least 256k. First, make a copy of the original disk, then put the original away, you won't need it. Next, you have to rename a couple of files. Rename AUTORUN.SYS to AWXE.COM, and AP.OBJ to A.OBJ. Now comes the fun part. Boot some sort of disk editor. I prefer using Disk Master found in DL 3 for making quick changes. The following procedure is for my version of the program. There may be other version that Atari has put out, so you might have to search the disk for these values. Also, these changes may work for the non-XE version of ATARIWRITER, but you'll have to find the correct sectors for the changes. Patchs: First change all the instances of D:AP.OBJ to Dn:A.OBJ (n is your drive number, I prefer 2). These are found on sectors 84, 315, 525, and 526. Next change the two instances of D1:AP.OBJ to Dn:A.OBJ (this will make the filename read Dn:A.OBJJ. Replace the second J with a $9B(EOL)). You'll find this on sectors 467. On sector 469 you'll see D1:AP.OBJ and on sector 204 you'll see AP.OBJ. Change the AP.OBJ to some other letters. Invalid DOS characters such as the double quote, dollar sign work well. These are the two checks the program makes to see you are trying to get a directory of the original ATARTIWRITER disk. They don't affect the SpartaDOS copy because you have to rename the AP.OBJ file to A.OBJ. To allow ATARTWRITER+ to use both the PROOFREADER and MAIL MERGE programs from the ramdisk, change the D1:MM.OBJ on sector 188 to Dn:MM.OBJ. Change D1:PROOF on sector 181 to Dn:PROOF. You must also make a few program changes to complete the process. First find the start of the AUTORUN.SYS file (now called AWXE.COM). Locate the bytes $AD $1F $D0 $C9 $05 $D0 $03 $4C $35 $22 and replace them ALL with $EA. These should be on the first or second line of your editors display. This change will disable the "RUN PD" option. Since you'll need a batch file to copy all the stuff over to the ramdisk, this option wouldn't work. To enable all the programs to use the ramdisk, you must disable the "CHECK DISK" routine. This routine checks to see if you have the correct disk in the drive. Since you are using a ramdisk, this option will cause problems. To fix this, find all the occurences of $C9 $C6. On my disk these are found on sectors 428, 448, and 516. A few bytes before those two, you should see $20 $53 $E4. You want to change the $20 $53 $E4 to $EA $EA $EA. On sector 516, you'll need to make one additional change. Find the bytes $4C $77 $E4 and change them to $F0 $03 $EA. There, now all you have to do is copy the files to a SpartaDOS disk. The batch file you'll want use will look similar to this: BASIC OFF <--No BASIC RD D2: /E <--Ramdisk with 64k reserved COPY A.OBJ D2: <--Copy Program COPY PROOF. D2:<--Copy PROOFREADER COPY MM.OBJ D2:<--Copy Mail Merge COPY GEMINI. D2:<--Copy a printer drvr COPY *.DCT D2:<--Copy supplimental dictionaries AWXE <--Run the program If you have problems or questions, please leave me a message and I'll try and answer them as soon as possible. If anyone is interested, I have also gotten Visicalc and other programs to work with SpartaDOS. ______________________________________ ZMagazine Archives ______________________________________ by Ron Kovacs Many people ask me each week about reading the older issues of ZMagazine. I decided the best way was to show you what is available is by capturing the listings from GEnie and CompuServe. This week GEnie is spotlighted and next week we will update you on CIS. Not every issue is available, but if you are missing a few issues and want them, you might find them here. Zmag Issues numbers were changed at the end of the 1986 calender year. We originally published the date as part of the filename. (Ex:ZMAG0527) This example would mean it was from May 27th, 1986. Since the change to a new year, a conflict might appear in filename. So, started the popular issue number as the filename. (Ex:ZMAG93) This example tells you it is Issue #93 of a regular edition. Special issues and feature releases may not have a issue number attached. If an issue contains (ZMAG59A) a letter after the issue number, this means it was updated or re-editted after the release of the original. A document or header in the issue should explain the reason for a change. I hope this fills you in on the filenames. Now the GEnie ZMag File Directory. No. File Name Address YYMMDD Bytes ====================================== 2873 FIX1050.TXT R.KOVACS 880130 6300 2875 REVIEWS.TXT R.KOVACS 880130 23940 2874 SPARTADOS.TXT KOVACS 880130 18900 2886 ZINDEX87.ARC KHK 880205 10080 1126 ZMAGJULY 15,JEFFWILL 860727 27720 1125 ZMAGJULY 22,JEFFWILL 860727 30240 2224 ZMAG#001.TXT KOVACS 870713 2520 1137 ZMAG0708.TXTJEFFWILL 860728 17640 1321 ZMAG0920.TXT KHK 860924 34020 1363 ZMAG1003 KHK 861005 22680 1377 ZMAG1011 KHK 861011 23940 1407 ZMAG1018.TXT KHK 861018 23940 1422 ZMAG1025 KHK 861025 28980 1431 ZMAG1101.TXT KHK 861101 30240 1442 ZMAG1108.TXT KHK 861109 30240 1459 ZMAG1115.TXT KHK 861116 31500 1483 ZMAG1122.TXT KHK 861123 28980 1499 ZMAG1129.TXT KHK 861130 31500 1505 ZMAG1206.TXT KHK 861206 37800 1532 ZMAG1215.TXT KHK 861214 18900 1610 ZMAG33.TXT KHK 870110 28980 1614 ZMAG34.TXT KHK 870113 25200 1651 ZMAG35.TXT KHK 870119 26460 1693 ZMAG36.TXT KHK 870127 26460 1714 ZMAG37.TXT KHK 870203 26460 1735 ZMAG38.TXT KHK 870209 27720 1756 ZMAG39.TXT KHK 870216 25200 1792 ZMAG40.TXT KHK 870225 31500 1802 ZMAG41.TXT KHK 870303 23940 1819 ZMAG42.TXT KHK 870311 25200 1829 ZMAG43.TXT KHK 870316 34020 1852 ZMAG44.TXT KHK 870323 37800 1922 ZMAG45.TXT KHK 870330 23940 1949 ZMAG46.TXT KHK 870406 22680 1964 ZMAG47.TXT KHK 870413 22680 1970 ZMAG48.TXT KHK 870420 21420 2003 ZMAG49.TXT KHK 870428 23940 2029 ZMAG50.TXT KHK 870504 22680 2059 ZMAG51.TXT KHK 870511 21420 2077 ZMAG52.TXT KHK 870518 32760 2085 ZMAG53.TXT KOVACS 870524 23940 2114 ZMAG54.TXT KHK 870601 35280 2120 ZMAG55.TXT SLOW-K 870605 31500 2129 ZMAG56.TXT KHK 870608 23940 2154 ZMAG57.TXT KHK 870616 30240 2175 ZMAG58.TXT KHK 870622 23940 2225 ZMAG59A.TXT KOVACS 870713 28980 2207 ZMAG60.ARC KHK 870706 17640 2212 ZMAG61.TXT KHK 870710 23940 2234 ZMAG62.TXT KHK 870717 23940 2251 ZMAG63.TXT KHK 870725 22680 2270 ZMAG64.ARC KHK 870731 20160 2297 ZMAG65.ARC KHK 870807 17640 2308 ZMAG66.ARC KHK 870814 22680 2322 ZMAG67.ARC KHK 870821 18900 2343 ZMAG68.ARC KHK 870829 15120 2377 ZMAG69.ARC KHK 870905 20160 2399 ZMAG70.ARC KHK 870911 16380 2426 ZMAG71.ARC KHK 870919 13860 2450 ZMAG72.ARC KHK 870925 16380 2501 ZMAG74.ARC KHK 871009 16380 2511 ZMAG75.ARC KHK 871017 18900 2535 ZMAG76.ARC KHK 871023 17640 2568 ZMAG77.ARC KHK 871030 17640 2604 ZMAG78.ARC KHK 871106 20160 2634 ZMAG79.ARC KHK 871113 22680 2667 ZMAG80.ARC KHK 871120 16380 2695 ZMAG81.ARC KHK 871128 12600 2724 ZMAG82.ARC KHK 871205 11340 2731 ZMAG83.ARC KHK 871211 20160 2770 ZMAG84.ARC KHK 871223 16380 2797 ZMAG86.ARC KHK 871230 30240 2808 ZMAG87.ARC KHK 880104 17640 2837 ZMAG88.ARC KHK 880111 21420 2857 ZMAG90.TXT KOVACS 880124 32760 2884 ZMAG91.TXT KOVACS 880131 36540 2896 ZMAG92.ARC KHK 880208 20160 1349 ZMAG927.TXT KHK 860928 20160 2926 ZMAG93.ARC KOVACS 880217 25200 2848 ZMAG89.TXT KOVACS 880119 42840 2002 ZPRINT.ARC SCHWARTZ 870427 13860 2323 ZPRINT23.BAS KOVACS 870822 6300 2407 ZPRINT24.BAS KOVACS 870913 6300 1870 ZPRINT4.OBJ KOVACS 870325 7560 1869 ZPRINT7.BAS KOVACS 870325 3780 1892 ZREAD31.XLB KOVACS 870328 8820 ______________________________________ Programming in Atari Basic Part 7 of a series ______________________________________ Part 7 LESSON 4 Version 1.07 Testing, Branching and Counters (C) COPYRIGHT 1987 by Jackson Beebe ------------------------------------ More on LOOPING: ------------------------------------ In the Part 6 we learned the powerful technique of sending program control back through previous lines of code, called LOOPING. As we said in Lesson 3, this is a prime feature that separates computers from calculators. The program can be sent back through a pile of source code lines, by using a FOR-NEXT or a simple GOTO statement, as: 10 DIM NAME$(15) 20 PRINT "Hello. Who are you? "; 30 INPUT NAME$ 40 PRINT:PRINT:PRINT 50 PRINT "Hi there ";NAME$ 60 PRINT:PRINT:PRINT 70 GOTO 20 ----------------------------------- TESTING: ----------------------------------- The process that unleashes the power of looping is TESTING. This gives us the ability to make decisions each time we fall through the code, as "should we continue?"; "should we quit?"; "is the input numerical?"; "is X > 42?"; etc. We can write lines of code that accomplish some purpose as guessing the Lotto number, and loop through multiple times. If we do that, we need to test on each pass for things like, "should we quit?"; "should output go to screen and/or printer?"; etc. This is accomplished by placing lines in the routine's code, usually at the beginning or the end, that test before or after execution. A test at the beginning of a loop is called a Top Test, and usually tests whether to go through the loop or not. A test at the end is called a Bottom Test, done after the loop is completed. This usually tests whether to loop back or not. For example: * * TOP TEST * * 10 X = 0 20 IF X > 10 THEN END 30 X = X + 1 40 PRINT X 50 GOTO 20 or 10 X = 0 20 X = X + 1 30 PRINT X 40 IF X < 10 THEN 20 50 END * * BOTTOM TEST * * Tests for various conditions and instructions may be grouped together in one location in a program, into "piles" of IF-THEN statements. I prefer this approach, as a pile of lines makes it easy to find and debug tests. IF-THEN statements execute pretty fast, but you'll notice some slowing when using a large number. ------------------------------------ BRANCHING: ------------------------------------ Testing, coupled with looping, gives us the ability to make decisions as we loop. An additional ability we have in programming, is BRANCHING. Branching is simply WHERE we send control from one of our tests. If our test asked "should I quit?", and got a YES response, we would probably send control to the line that had the END statement, ending the program. Possibilities begin to unfold like petals of a flower, as you "grok" the concept of lines of code with multiple tests for multiple things, sending control to multiple possible places, where multiple things may happen, and on and on and on. Wow! Now THAT'S programming. That's what you've been waiting for, right? Now, how do we code these tests? These CONDITIONAL TRANSFER OF CONTROL statements? They are the IF-THEN statements. ------------------------------------ IF-THEN statement: ------------------------------------ This statement takes the basic form of: line# IF (some test) THEN (some statement) ------------------------------------ RELATIONAL Operators: ------------------------------------ We can test for standard mathematical relationships with the RELATIONAL Operators which are: = equal to < less than > greater than <= less than or equal to >= greater than or equal to <> not equal to Some examples: 15 IF X > 89 THEN GRADE$ = "A" 95 IF A <> B THEN C = A + B 135 IF NUM = 99 THEN ? "Bye":END 20 IF X > 14 THEN 1200 10 IF NAME$ = "JACKSON" THEN 135 Characters may be tested for alphabetical order, equal to, greater than etc. ------------------------------------ LOGICAL Operators: ------------------------------------ Tests may be combined, or substituted using the LOGICAL Operators: AND and OR For example: 110 IF X >14 AND DAY$ = "M" THEN 1200 We can test for a range of numbers as: 15 IF X > 0 AND X < 100 THEN 100 25 IF X < 0 OR X > 100 THEN END Line 15 above, accepts numerical input to the variable X, that is between 0 and 99.999+. Line 25 rejects input OUTSIDE the range of 0 to 100 (same thing.) Although it looks easy, knowing when to use AND and when to use OR in your tests, will be very confusing. As you reason out the logic of multiple tests, you will make the wrong choice many, many times. Be mistrustful of your tests, until they are proven correct by trying good and bad data for input. Always check the use of OR and AND when debugging programs that don't work right. Try numbers on each side of the limits, to make absolutely sure you've got it coded right. These really get confusing when we string tests together as: 70 IF (X> 0 AND X< 10 AND FLAG = 1) THEN FLAG = 0 This line tests for three conditions, and if True, sets FLAG = 0. Note parenthesis used between the IF and THEN portion of the statement. These are often required to keep things straight, and always allowable. Note the code following the THEN in this case, is not a GOTO, but simply an instruction. Here's a test to Quit: 80 etc 90 DIM KEYIN$ (1) 100 ? "QUIT (Y/N) ? "; 110 INPUT KEYIN$ 120 IF KEYIN$="Y" or KEYIN$="y" THEN ? CHR$(125):END 130 etc This code dimensions a one character string variable KEYIN$ for input. It tests for both an upper and lower case y, clears the screen and ends the program if found. Testing for both upper and lower case is the best idea, as the program will work, regardless of how the user has the upper/lower case toggled. This is an example of error checking the input, a process that bulletproofs a program against incorrect input causing a crash. This is often a factor that separates smooth professional programs from rough hacks. We will expand on this process as we learn. Note the quotes around alphabetic characters being tested for, and that Atari BASIC is forgiving about whether you use spaces before and after the relational operators, and variables, etc. Also note we MUST restate the variable when using AND and OR. Here's WRONG code that WON'T work: (wrong) 10 IF A<6 AND >10 THEN END (right) 10 IF A<6 AND A>10 THEN END The syntax checker in the built-in BASIC editor will catch this error. Multiple statements may be hung on the end of an IF-THEN, separated by colons. The code following the THEN will be executed when the IF-THEN statement tests TRUE. All code past the THEN will be executed up to the permissible maximum line length of three screen lines. The code following the THEN is never executed if the statement tests False. For example: 10 FOR X = 1 TO 25 20 IF X>=6 AND X<=10 THEN ? X 30 NEXT X 40 END This program prints: 6 7 8 9 10 The equal sign tests for EXACTLY equal to, and 5.9999 is NOT equal to 6. This can be tricky. It is common practice to use < and > to test for numbers, or <= and >= when possible, to avoid numeric errors resulting from multiplication or division causing slight inequality. Strings may be tested, and < and > will test for alphabetical order of the first letters of strings. Again, don't trust your eyes and brain to know whether you've arranged your AND's and OR's, parentheses and logic correctly. It always LOOKS right. Use correct and incorrect input, and make sure by trial and error that everything is correct. Some BASIC's support an ELSE addition to the IF-THEN statement, but Atari BASIC does not. Don't worry, we don't really need it. You can always arrange code to achieve the effect you want. When an IF-THEN statement is False, execution resumes at the very next line, and the IF-THEN is NOT executed. The opportunities, and combinations are endless, and knowing a few good "hacks" is what separates new from experienced programmers. We will continue to learn about IF-THEN statements for a long time. ______________________________________ ZMagazine Issue #94 February 22, 1988 (c)1988 SPC/Ron Kovacs ______________________________________
- Next message by date: Atari SIG: "Z*Magazine: 29-Feb-88 #95"
- Previous message by date: Atari SIG: "Z*Magazine: 15-Feb-88 #93"
----------------------------------------- Return to message index