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here is: Don't always expect books to tell you what the computer is going to do. 2) Real Number Input It's a frustrating thing to be forced to write your own routine to accomplish a certain task when you know.that such a routine already exists, but is inaccessible to you. One such example in the Pascal system is the conversion of a string of characters into a number. The system "knows" how to do the translation - it happens every time a value is typed in at the keyboard or read from a text file. But if you want your program to do the same thing, you'll have to write your own procedure to do it, because the system hides the procedure from you. Let's assume you want to write a routine to translate a string of characters into a real number. One of the things you should know while writing such a module is the smallest and largest positive real numbers the system can represent, so your routine can avoid over- and underflows. To determine these values, you might write a program like this: program readreal; var x: real begin while TROE do begin write('Enter x':); readln(x); writeln('x = ',x) end end. This program will blow up with a floating point execution error if you type in a number too large or too close to zero. With experimentation, you'll find that the largest real number Pascal can represent is approximately 3.40E38, and the smallest positive real number is approximately l.18E-38. Or, more accurately, these are the limits on the numbers one can enter using the READ procedure. A problem arises when you try to incorporate the smaller number into a program. If you use the lines: const TINY = 1.18E-38 or even: IF X >+ l.18e-38 THEN ... . .. the Pascal compiler will ·(Kaboom!) self-destruct on attempting to translate the number. To be more precise, the compiler program itself will halt with a floating point execution error. What does this mean? Apparently, there are actually two different routines in the Pascal system for translating strings of characters into real numbers: one used by the READ statement, and one used by the compiler. And the routine the compiler uses will not translate some numbers which offer no problem to the other one. Here's an example of another symptom of having two different real number conversion routines: program realtest; var x: real; 56 Apple Orchard begin repeat write('Enter x':); readln(x); writeln('x = ',x) until x = 2. 718281828 end. Most programmers know better than to compare two floating point numbers for exact equality. But in this example we might reasonably expect such a comparison to work If you enter "2.718281828" the program should react normally, shouldn't it? Well, in Apple Pascal, it doesn't. The two different conversion routines translate the strings (in the program and in the READ statement) into two ever so slightly different floating point representations. The comparison fails, and the program continues on. There's no good reason why there should be more than one such routine in the Apple Pascal system. (The one you may have to write will be at least the third!) A major benefit of using a modular programming language like Pascal is that one can write a single reliable procedure to accomplish a given task, and use it in a variety of applications. The moral: Duplicated programming effort is not only wasteful, but it can lead to -er, "features"- in your programs. 3)Real Number Output . We just discussed the frustration one feels when a routine must be written to do something the system already knows how to do. Another kind of pain results when the language texts and system documentation spell out in detail what. a given funtion does in different circumstances -.and th~n m practice the function actually does something entirely different. Such is the case with the standard procedures WRITE or WRITELN when they are used to output real numbers. Most texts, as well as Apple's own documentation, (see the Apple Pascal Language Reference Manual, Pages 36-37) describe the procedure as follows: The statement: WRITELN(X: W: D) ... will cause the real number X to be written, after it is converted to a string. The optional variables W and D control the output format; Wis the minimum number of characters that will be printed, and D is the number of digits to be printed after the decimal point. . So far, so good. Consider the program m Listing 2: LISTING 2 program testwrite; var w, d, i: integer; x: real; begin x := 0.123456; w:=20; d := 8; for i := 1 to 10 do begin writeln(x: w: d); x*·(lO*x) end end. ' ,
BUSINESS FORM PROCESSING Application Memo #1= INVOICES BLANK FORM OROER CRT SCREEN ~U ,. .. u}w~ INVOICE ' -== Other VersaForm Uses: • Purchase Orders • Professional Billing • Inventory Ledgers • Job Costing • Personnel Records Send for Application Note INV-01 r- .___ REPORTS RECEIVABLES: BY DATE ANO/OR CUSTOMER YEAR TO DATE BY CUSTOMER SALES BY PRODUCT DAILY INVENTORY ACTIVITY MONTH'S RESULTS BY SALESPERSON MAIL LABELS Now there's a way to quickly automate specific areas of your business ... using existing forms. In a single session you can emulate a standard invoice on a personal computer (as shown on side). Automatic filling, calculating and data checking features to speed error-free processing. It's called Business Form Processing, a brand new concept in desktop computing. Producing management reportsthat used to take days now takes minutes. Just specify which items contained within your form are to be sorted, sub and summary totalled. Each report as shown took only minutes to specify, and minutes to produce. It's the combination of the easy-to-use reporting facility with its powerful forms emulator that makes Versa Form more than just a data base. You can use existing forms. With a simple output formatting module, VersaForm lets you overprint processed information to a pre-printed form, or to blank paper that becomes its own custom form. It even customizes your output to your printer's line spacing and number of characters per line, and can omit confidential data from final customer drafts. If you have a form, we've got the system and solution to higher productivity. Visit your local computer store where Apples are sold. VersaForm supports Apple II and Apple Ill. Hard Disk versions available Business Form Processor Applied Software Technology 14125 Capri Drive Los Gatos, California 95030 (408) 370-2662
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Almlr!rtTEArt~. 110rtAL ~PPLE COAET
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Buy Five Megabytes Of Winchester St
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Vol. 3 No. 2 May-June 1982 Entire c
Page 9 and 10: One Apple and$1,550 can make a lot
Page 11 and 12: "NIBBLE® IS TERRIFIC" (For Your Ap
Page 13 and 14: Pla11ti114 a SEEd ••• THE VAN
Page 15 and 16: Yes, please send me a dealer list f
Page 17 and 18: •For ttie 48K Apple* II with Appl
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Page 77 and 78: WILL THE REAL APPLE PASCAL PLEASE S
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