<><><><>¢ MODULAR PROGRAMMING IN ATARI BASIC!¢ ¢ This is Part I. (LOOK FOR PART II in¢ the next OL' HACKERS newsletter!)¢¢ by Ron Fetzer-memberof OL'HACKERS NY¢ This article has been submitted¢ to The ATARI CLASSIC magazine!¢¢ How many times have you said "I¢ wish I could write a long program¢ like Print Shop"? Have you ever¢ wondered how these long professional¢ programs were written? Is there a way¢ I could write a program like this?¢ The answer is yes! There is a method¢ of programming not widely know among¢ BASIC programmers called Modular¢ Programming. If you learned¢ programming by yourself, like I did,¢ you know the limitations of Brute¢ Force programming. I usually hit the¢ wall around 200 lines before I become¢ hopelessly lost.¢ There is an easy and better way¢ of writing programs. If you can write¢ 15 lines of code then you can write¢ modular programs that easily exceed¢ the memory of your computer. The¢ central idea of modular programming¢ is that you break a big task into¢ small units. Thus you are concerned¢ with only a small part of the task at¢ any one time. Programming will again¢ become fun and very satisfying. The¢ academic term for this method is¢ called Structured Programming. It has¢ been kept a secret from BASIC¢ programmers for a long time. The¢ professionals use it all the time.¢ Atari BASIC is very well suited for¢ this method of programming because it¢ has a very compact structure that can¢ be learned very quickly.¢ If you use modular programming¢ you will write short modules and¢ string them together to create a¢ whole program. You will have many¢ benefits. 1. Your program now will be¢ easy to write the first time.¢ 2. Your program is easy to read by¢ anyone.¢ 3. It can be changed or modified¢ easily.¢ 4. Bugs can be found instantly.¢ 5. The program is self documenting.¢ 6. Large programs do not present a¢ problem anymore.¢ 7. The programs will be elegant.¢ 8. Programming will become fun again¢ because there is no more¢ frustration.¢¢ To start with you write out your¢ ideas for the program in English. You¢ make an outline just the way you did¢ for a composition in High School.¢ Next you make a block diagram. That¢ shows you how many modules you need¢ and how they are connected. Then you¢ write a skeleton program. This is to¢ see that the modules execute in the¢ right order. Finally you flesh out¢ the skeleton program into a complete¢ program.¢¢ Writing the code for the program¢ is the easiest part and should take¢ the least amount of your time.¢ Planning the program should take the¢ most part of your time. This looks¢ like a lot of work. It is not. It can¢ be sketched out very quickly. Each¢ step leads to the next step. You have¢ now created a blue print to follow¢ that is guaranteed to work. After you¢ have tried this method once you will¢ never go back to Brute Force¢ programming again.¢¢ In modular programming you start¢ out with the most general module¢ first and then each succeeding module¢ becomes more specific. The first¢ module is the control module. The¢ control module is the head or brain¢ of your program. It controls your¢ program. The sub modules do not¢ influence the control module. In¢ Atari BASIC you use the GOSUB -¢ RETURN function for all modules.¢¢ My better half the other day¢ said "Dear can't you write a program¢ that prints the addresses on the¢ Christmas Card Envelopes? Sticking on¢ labels looks so commercial". Thus was¢ born the idea of the Envelope¢ program. Why stop with Christmas¢ Cards? Lets do business envelopes and¢ large 7 X 9 envelopes also. Below is¢ the outline in English of the ideas¢ that I want in my program.¢¢ ENVELOPE PROGRAM¢¢ I MAIN HEADING¢ A)DIM SECTION¢ B)SCREEN COLORS¢ C)RETURN ADDRESS¢ D)FORWARDING ADDRESS¢ E)MENU¢¢ II MENU¢ A)CHRISTMAS CARDS(5 X 7)¢ B)BUSINESS ENVELOPES(4 X 9.5)¢ C)LARGE ENVELOPES(7 X 9)¢ D)END¢¢ III PRINT SECTION¢ A)PRINT RETURN ADDRESS¢ B)PRINT FORWARDING ADDRESS¢¢ I want the user to have a choice¢ of screen colors while the program is¢ on the screen. The user should type¢ his return address only once and then¢ have a choice of envelope sizes. The¢ menu should also have an END option¢ so the user can exit.¢¢ Now I have a general idea of¢ what I want in my program. The next¢ step is to write a block diagram.¢ This block diagram will show you how¢ many modules you need and the range¢ of line numbers. Each line above will¢ become a module.¢¢ A block is a section of code¢ that performs one action. A module¢ can contain one or more blocks. A¢ block as well as a module should¢ follow the rule of straight sequence,¢ that is the entry point should be at¢ the top and the exit at the bottom of¢ the block or module. Do not jump out¢ of the module or block with a GOTO or¢ you will have spaghetti code.¢¢ It is important not to skip this¢ step. Sometimes you will have modules¢ calling sub modules or sub sub¢ modules. Each module is in the form¢ of a GOSUB - RETURN. For each module¢ I skip by 500 numbers to make it easy¢ on myself. The block diagram below¢ follows the outline that I did before¢ in English.¢¢ ENVELOPE BLOCK DIAGRAM¢¢ 10 - 499 CONTROL BLOCK¢ 500 - 999 DIM SECTION¢ 1000 - 1499 SCREEN COLORS¢ 1500 - 1999 ENTER RETURN ADDRESS¢ 2000 - 2499 MENU¢ 2500 - 2999 ENTER FORWARDING ADDRESS¢ 3000 - 3499 * CHRISTMAS ENVELOPES¢ 3500 - 3999 * BUSINESS ENVELOPES¢ 4000 - 4499 * LARGE ENVELOPES¢ 5000 - 5499 PRINT RETURN ADDRESS¢ 5500 - 5499 END¢ * These modules use also the sub¢ modules of PRINT RETURN ADDRESS and¢ FORWARDING ADDRESS.¢¢ The control module calls all¢ other modules. Each module returns¢ eventually to the control module¢ where it is directed again to the¢ menu module. A good program is easy¢ to read, consistent and self¢ documenting. You now have a outline¢ of your program with all its¢ modules.¢¢ It is now so easy to set up a¢ skeleton program. The skeleton¢ program will confirm the correct¢ execution of your modules. Later on¢ the skeleton program gets fleshed out¢ to the full program. Each module in¢ the skeleton program will have a¢ PRINT statement in it to show the¢ function of the module when the¢ program is run. Later on when you¢ flesh out the skeleton program you¢ will take out this print line. Below¢ is the skeleton program.¢¢ ENVELOPE SKELETON PROGRAM¢¢ 0 GOTO 10¢ 1 SAVE "D:SKELETON.ENV":CLR¢ 5 REM SKELETON PROGRAM FOR¢ "ENVELOPE.ATR" VER 1.0 IN ATARI BASIC¢ BY RON FETZER 9/92¢ 10 REM CONTROL¢ MODULE*******************************¢ ******¢ 20 ? CHR$(125):GOSUB 500:REM DIM¢ SECTION¢ 30 GOSUB 1000:REM SCREEN COLORS¢ 40 GOSUB 1500:REM RETURN ADDRESS¢ 50 GOSUB 2000:REM MENU¢ 60 GOTO 50¢ 500 REM DIM¢ SECTION******************************¢ *********¢ 510 ? :? "DIM SECTION":GOSUB 30000¢ 520 RETURN ¢ 1000 REM SCREEN¢ COLORS*******************************¢ *****¢ 1010 ? :? "SCREEN COLORS":GOSUB¢ 30000¢ 1020 RETURN ¢ 1500 REM RETURN¢ ADDRESS******************************¢ *****¢ 1510 ? :? "RETURN ADDRESS":GOSUB¢ 30000¢ 1520 RETURN ¢ 2000 REM¢ MENU*********************************¢ ************¢ 2010 ? :? " MENU:":? :? ¢ 2020 ? "1. CHRISTMAS CARDS(5 X7)"¢ 2030 ? "2. BUSINESS ENVELOPES(4 X¢ 10)"¢ 2040 ? "3. LARGE ENVELOPES(7 X 9)"¢ 2050 ? "4. END"¢ 2060 ? :? " SELECT A¢ NUMBER";:INPUT N¢ 2070 ON N GOSUB 3000,3500,4000,5500¢ 2080 RETURN ¢ 2500 REM FORWARDING¢ ADDRESS******************************¢¢ 2510 ? :? "FORWARDING ADDRESS":GOSUB¢ 30000¢ 2520 RETURN ¢ 3000 REM CHRISTMAS¢ CARDS********************************¢ *¢ 3010 ? CHR$(125):GOSUB 5000¢ 3020 GOSUB 2500¢ 3030 ? :? "CHRISTMAS CARDS(5 X¢ 7)":GOSUB 30000¢ 3040 RETURN ¢ 3500 REM BUSINESS¢ ENVELOPES****************************¢ ****¢ 3510 ? CHR$(125):GOSUB 5000¢ 3520 GOSUB 2500¢ 3530 ? :? "BUSINESS ENVELOPES (4 X ¢ 9.5)":GOSUB 30000¢ 3540 RETURN ¢ 4000 REM LARGE¢ ENVELOPES****************************¢ ******¢ 4010 ? CHR$(125):GOSUB 5000¢ 4020 GOSUB 2500¢ 4030 ? :? "LARGE ENVELOPES(7 X¢ 9)":GOSUB 30000¢ 4040 RETURN ¢ 5000 REM PRINT RETURN¢ ADDRESS******************************¢ 5010 ? :? "PRINT RETURN¢ ADDRESS":GOSUB 30000¢ 5020 RETURN ¢ 5500 REM¢ END**********************************¢ ************¢ 5510 ? :? "END OF PROGRAM":GOSUB¢ 30000¢ 5520 END ¢ 5530 RETURN ¢ 30000 REM TIME DELAY LOOP USED ONLY¢ IN THE SKELETON PROGRAM¢ *************************************¢ ********************¢ 30010 FOR T=1 TO 180:NEXT T¢ 30020 RETURN ¢ 30030¢ REM**********************************¢ ***********************¢¢ I separate each module with a¢ REM and the module name. Then I fill¢ in the rest of the module separator¢ with asterisks until I have two¢ screen lines. In this way I can¢ separate very clearly each module in¢ the program.¢¢ The time delay loop in lines¢ 30000 to 30020 is used only in the¢ skeleton program to slow down the¢ execution of the program so you can¢ see if it executes correctly.¢¢ In conclusion in modular¢ programming the most important part¢ is the planning. Write out an outline¢ in English of your ideas for the¢ program. You must set up a block¢ diagram to show what modules you¢ need. The control module should be¢ the first module. You must write a¢ skeleton program to see if your¢ program will execute correctly.¢¢ Each block and module follow the¢ law of straight sequence. You enter¢ at the top and exit at the bottom or¢ the end of the block or module. This¢ is the natural expectation in reading¢ a sequence and thus should be¢ followed without fail. Do not jump¢ out of a block or a module with a¢ GOTO.¢¢ Now it will be so easy to finish¢ your program. You know it will work.¢ You know that you can complete each¢ module at your leisure. You know you¢ can find a bug instantly. You know¢ you are going to be successful.¢¢ Programming will become fun¢ again. You now can be proud of your¢ program, not only does it work but it¢ is also professionally written. Your¢ program now will compare with the¢ best of them.¢¢ In the 2nd part of this series I¢ will show you how to flesh out and¢ polish your program and complete it.¢¢ I am a member of the OL' HACKERS¢ ATARI USERS GROUP in Oceanside N.Y.¢ If you want more materials on this¢ subject we have the "PROGRAMMING¢ KIT". It is a 3 disk double sided¢ disk set. It discusses this subject¢ in greater detail and uses TURBO¢ BASIC. It is available for $7.00 from¢ us. Write to Alex Pignato, 3376 Ocean¢ Harbor Dr., Oceanside N.Y. 11572.¢ Make the check payable to Ron¢ Fetzer.¢¢ LOOK FOR PART 2¢ <><>¢
