Where do you get more help and information about your Atari? Obviously, Creative Computing is one source, and there are several others. If you are a beginner, the Atari Basic self-teaching guide that came with your computer will get you started. When you send in your warranty card, you will receive the Atari 400/800 Basic Reference Manual, which is much better, and actually answers most of your questions. I had three questions when I first started programming the Atari:
1. How do you concatenate strings?
2. How do you array strings?
3. How do you obtain keyboard input without stopping the program?
Atari had given me the name of someone in the plant to call for questions, so I called and left my questions. Within hours they called back with the answer; "We don't know." The next day my preliminary reference manual arrived, and it had answers to all three questions! The answers were not easy to find, but they were there.
1. To concatenate a string variable, follow these steps:
a. Dimension the receiving string large enough to hold the combination.
b. Determine the length of the original string with the LEN function.
c. Assign the string to be combined to the next location in the receiving string.
Here is a program to do it:
10 DIM A$(10):DIM B$(5)
50 PRINT A$
2. String arrays are difficult in Atari Basic. Essentially, you have to dimension a very large string, store all other string data as substrings, and do your own bookkeeping to keep track of where each item is. The Alpha-numeric Sort routine in Appendix A of the Reference manual uses this method. One advantage of Atari Basic is that there is no arbitrary limit to the size of a string, as there is in Microsoft Basic, so there is a lot of flexibility.
3. To strobe the keyboard, PEEK location 764 in memory to determine when a key is pressed. To obtain a single character from the keyboard, OPEN the keyboard as an input device and use the GET command:
10 OPEN #1,4,0,"K:"
20 GET #1,A
30 PRINT CHR$(A)
40 X=PEEK(764):IF X<255 THEN PRINT X
50 GOTO 10
Other sources of information include Compute! magazine which divides its attention between the Pet, the Atari, and the Apple. The cost is $20.00 a year for 12 issues. For a subscription, write: Compute!, P.O. Box 5406, Greensboro, NC 27403.
Two magazines published soley for Atari owners are A.N.A.L.O.G. (6 issues, $12.00 a year) and ANTIC (6 issues, $15.00 a year). Write to A.N.A.L.O.G. at P.O. Box 615, Holmes, PA 19043 and to ANTIC at 297 Missouri Street, San Francisco, CA 94107.
I have since received the regular Basic Reference Manual, and it is even better than the preliminary one. One nice new feature is an excellent memory map. Some information is still not released, but I get the impression that this is because Atari is reluctant to release it in its preliminary form, not because they are trying to hide something. I know that they have been particularly helpful to friends of mine who have signed non-disclosure forms.
One excellent source of information is Iridis. Iridis was first advertised as a magazine, but now describes itself as "a series of tutorials about the Atari Personal Computer." It is sold, not by subscription, but by individual issues.
Iridis I contains four programs with explanatory articles, three columns, and an explanation of their format for printing control characters. You can purchase it either with the programs on cassette ($9.95) or on disk ($12.95).
The four programs include "Clock," a high resolution wall clock with moving hands, ticking and chimes; "Zap," where a joystick-controlled snake moves around the screen eating bits of food and growing; "Logo," which displays the Iridis logo in dozens of different shades, with instantaneous changes from one color to another; and "Polygons," which constructs geometric patterns.
Each program is listed, and a "behind the scenes" article following each listing explains the program in detail. These listings are very well done, and contain fascinating glimpses into programming techniques. For example, you can test to see if the START button is pressed by checking to see if memory location 53279 contains anything other than 7.
The three columns are "Novice Notes," with programming tips for the beginner, "Hacker's Delight," which goes into detail about how the machine works, and "Oddments," which contains features too short to deserve an article, but too significant to be ignored.
Iridis I comes in manual format, 6 inches by 9 1/2 inches, and contains 32 pages. The print is quite small, and appears to be typeset with a small computer, word processor and printer. Except for a chart on the last page showing the Atari control characters, there are no illustrations.
You may order Iridis from The Code Works, Box 550, Goleta, CA 93017
As a closing feature, here is a calculator program I use frequently to balance my checkbook, do my taxes, and for any other adding machine functions. Although it is very short, it is one of my favorite programs. To clear the memory, enter the present value of the accumulator (B) as a negative number.
10 INPUT A:B=B+A:PRINT B:GOTO 1O