Writing Applications The first thing that has to happen is that you have an idea. When this happens, program as usual, but avoid the following variables,size of array follows: m$(3,65,13) z$(12) l(31) p (16,2) z(30,7) f$(3,65) t$(10,3) s$(2,11,2) d(9) r(4,2) drv f fil bot top error store recall udglb udghb screen delete show app oloa win g$ s t s1 t1 w1 sel opt addr You can use any other variables at will, and some of those listed above can be used, but to be on the safe side it is better that they aren't. Your program shouldn't be too long, about 4.5k is the MAXIMUM size which can be used, about 2k (including storage areas) would be the best size. Obviously the smaller the application the more can be in memory at any one time, however, I have prevented the computer from loading an application if the available memory is smaller than 1500 bytes. Up to 8 applications could (theoretically) be in memory, however 2 is probably the maximum practical. Ok, so you have written you program, what next? Firstly renumber your program (so that means you can't use calculated GOTO's/GOSUB's) to any of these start lines: 1500,1550,1600,1650,1700,1750, 1800,1850 these correspond to app(lication) numbers. Then design an icon (2 chars deep by 3 chars wide) and place it anywhere in memory (I prefer to keep them close to the other icons in memory (about 52736 onwards)). Save your icon as "what_ever_the_application_is to be_called + .RES" Then on line 624+app_number PRINT in the input area your icon (remember to switch udg banks). It doesn't matter where it is printed in the input area, but it is best to stick to the following x coordinates: App_number X-coord 1 0 2 4 3 8 4 12 5 16 6 20 7 24 8 28 Now, on line 390+app_number enter: IF t>=[x-coord) AND t=<[x-coord+3] THEN LET app=o1: LET n=[start line of app]: LET i$="[Name of Application]": LET a$="[Information about the application, up to 80 chars, right margin set at 20]" There is one more thing that has to be done, set up a DATA statement telling the computer which lines have to be deleted when the application is removed. On the first line of your application (before any other data statements in your application). Put the start of finish of any lines loaded in with the application. If you had used app_number 1, and had followed the numbering policy I have, given your data statement would read DATA 391,391,625,625,1500,1548 Note that the last number is 1548 and NOT 1549 this is because on line 1549 in this example must read: 1549 DATA 10000,0 This signifies the end of the deleting data, this line is then deleted itself. Routines to Help you Program I have included in the program a number of useful routines. They are usually called via variable to save memory: Line Function 800 Menu routine Entry conditions: x,y coords of top right corner le length of menu bar opt number of options Exit conditions: sel option selected store stores screen in memory recall recalls screen from memory error Error/message window Entry condition: i$ message, max length=60 chars right margin=20 chars Exit conditions: err=0 cancel selected err=2 retry selected 910 will load a file Entry condition: g$ 16 char filename g$ takes the form of: g$(1)=file type: chr$ 3 = font chr$ 4 = basic chr$ 7 = tool chr$ 8 =screen$ chr$ 9 = game chr$10 = app These are the loadable file types, there are others. GAME files and TOOL files are BASIC programs. g$(2 to 3) = user area g$(4 to 5) = drive including colon g$(6 to 13)= file name g$(14 to 16)=file type 930 Check a +3 DOS filename from an user input for invalid characters Entry conditions: a$ filename err = 1 if filename OK err = 0 or err = 2 if filename bad 950 Input text, this is only really suitable for filenames. Entry conditions: x,y coords of input Exit conditions: a$ text, max length is 7 chars If you wish to use to pointer in a routine then call with USR 49152, the x coord is in 49531 and the y coord is in 49532 Best of luck with your applications writing - Dominic Morris 6 June 1992
