Classic Computer Magazine Archive ANTIC VOL. 4, NO. 11 / MARCH 1986

starting out


Get started programming your Atari

by David Plotkin


New Owners Column is for Antic readers who want to learn how to program their brand-new Atari 800XL or 130XE computers-or for those who have owned their Ataris awhile but only used them to run commercial software.
   Programming is the ultimate challenge for computer users. As we start these lessons, I won't assume you know anything about your computer except how to hook it up. Before we are done, you should be fairly familiar with programming. I hope you enjoy the trip.

In order to tell your computer to perform specific tasks, you need a programming language. You can't simply type English words into your computer and expect it to understand such an illogical vocabulary. Computers are very literal-minded (annoyingly so) and demand extremely precise and consistent communications.
   Your Atari computer comes with a built-in programming language called BASIC which is quite powerful, comparatively easy to learn and widely used by non-professional programmers. Most Antic listings are written in BASIC.
   Like a foreign language, BASIC has its own words, called commands. These commands tell BASIC what you want it to do. Fortunately, there aren't very many commands to learn-and you can get going without knowing every command. Learning to program in BASIC consists of learning the commands and how to use them, plus becoming familiar with some of the special powerful features of your Atari computer.

BASIC is automatically turned on when you turn on your computer. The word READY appears on the screen telling you that BASIC is present.
   One of the first essentials you must learn is how to move programs between your computer and your storage disks-you don't want to retype the whole program every time you use it. BASIC makes it very easy to perform these operations with the SAVE and LOAD commands.
   To SAVE a program you have entered (typed into the computer) just type:
   The square brackets [] around the word RETURN are used by Antic to show that you should press the key marked RETURN. We'll use the same [ ] symbol to indicate other special keys on the Atari keyboard. Don't type in the brackets.

   To LOAD a program you previously
   SAVEd, just type:

   Type these (and any other) commands exactly as shown! In this case, you must include the two sets of quotation marks ["] and the colon [:], and type entirely in capital letters. However, in Antic the word FILENAME always just stands for whatever name you give your file, so use the name of your choice instead of FILENAME.
   An Atari filename can have up to eight letters. If you wish, you can also add a period and a three-letter extender- "D:QQQQQQQQ.EEE" could be a filename. The filename can have less than 8 letters, and the extender is not required.

In order to tell your computer what to do, you will use the keyboard to enter commands. The keyboard of your Atari looks quite a bit like a typewriter, but there are some important differences. Set off from the rest of your keyboard are a series of function keys (labeled [HELP] ,[START], etc.). Many commercial programs use these keys, and I will teach you how to use them in your own programs.
   During the programming process, the only function key that actually does anything is marked [RESET]. This key clears your screen if you are programming and will stop a program which is running. The [RETURN] key at the right of your keyboard is used for telling the computer you have finished entering a comand or a line of commands.
   For example, to make a BASIC program which you have LOADed from the disk start to RUN, you would type RUN and press the [RETURN] key. When entering (typing in) a BASIC program, such as the one included with this column, you would press the [RETURN] key at the end of every line. A program line is a series of instructions that begins with a line number.
   Another key you won't find on the typewriter is the [BREAK] key in the upper right corner. This key will normally stop a running program. It will also move the white square on the screen (called a cursor) down the screen without entering the command or line the cursor is on- pressing the [RETURN] key would enter the command or line.
   The [INVERSE VIDEO] key is in the lower right corner of your keyboard, marked with a small two-color square. It prints characters on your screen in inverse (dark characters against a light background).

Whatever you type on your keyboard while you are programming will show up on the screen. The next letter you type will show up where the white cursor block is located. Some special keys on your keyboard allow you to move the cursor around the screen, so that you may type anywhere. This is especially helpful when you are editing a program you have written, and need to get to a particular place on the screen to change something.
   Four keys to the right of the keyboard are marked with arrows. The cursor will move in the direction indicated by these arrows when you hold down the [CONTROL] key and at the same time press an [ARROW] key. Three additional editing keys are in the upper right corner of your keyboard, alongside the [BREAK] key.
   The [CLEAR] key will blank the screen if you press it while the [CONTROL] or [SHIFT] keys are held down. This does not erase your program, it only clears the screen. The [INSERT] key will insert a space if used with the [CONTROL] key, and will insert a line when used with the [SHIFT] key.
   Finally, the [DELETE BACK SPACE] key will move the cursor one space to the left, erasing whatever was in that space. But when you use this key while holding down [CONTROL], it deletes whatever is under the cursor-and everything on the right moves one space leftward. To delete the whole line the cursor is on, hold down the [SHIFT] key while pressing the [DELETE] key.

Whenever possible, your Atari tries to help you learn to program by pointing out when you make errors. These error messages are essentially of two types. The first type of message occurs when you are entering a program and make a mistake so the computer doesn't understand what you want. This is called a syntax error because it indicates that some is wrong in the syntax (grammar) of your program line.
   For example, suppose you typed PRONT instead of PRINT. After you press [RETURN], the computer will reprint the line with the word ERROR. And it highlights the point at which it couldn't understand your commands. You may either retype the entire line carefully, or use the editing keys described above to delete the word ERROR, correct the mistake, and then press [RETURN] again.
   The second type of error occurs when you are actually running a program. Naturally enough, it is called a programming error. The program will stop and display a numbered error message on the screen. You will then have to go to your manual to figure out what the message means and what went wrong. This is often difficult and is known as "debugging".
   For our purposes right now, if the program stops and gives you a numbered error message, the thing to do is check and make sure that the program was typed in exactly as printed. To start this check, type LIST and press [RETURN]. To pause the listing as it scrolls (goes by) on the screen, press [CONTROL] and the [1] key at the same time. Press them again to resume the scrolling movement.

Included in this issue's Software Library pages is "My Hello Program." Type it in carefully and SAVE it to disk before you RUN it. At the end of each of the numbered lines press [RETURN], to enter that line's information into the computer memory. Take care of any errors as outlined above. For now, don't try to use the TYPO II automatic program-checker. When you are finished typing it in, SAVE it to disk by typing "D:MYHELLO.BAS" and then pressing the [RETURN] key. This process ensures that if your computer's memory is erased by an accidental power outage, you can simply turn the Atari back on and LOAD your program back into memory from disk, as described above.
   Now, type RUN and again press [RETURN]. You may not understand the way this program works yet, but before long you will.

(New Atari owners will find additional details about topics covered by this series in Lon Poole's excellent book, Your Atari Computer ($17.95), Osborne/McGraw-Hill Publishing Berkeley CA. -ANTIC ED)

David Plotkin is a chemical engineer and a longtime Antic author/programmer.

Listing 1   MYHELLO.BAS Download