It took Michaelangelo 1460 days to paint theceiling of the Sistine Chapel.But it'll take you less than one to begin creatingyour own Apple-generated <strong>graphics</strong>!How? See over for d<strong>et</strong>ails . ..111111NO POSTAGENECESSARYIF MAILEDIN THEUNITED STATESBUSIN ESS REPLY MAILFIRST CLASS PERMIT N0. 1976 BOWI E, MDPOSTAGE WILL BE PA ID BY ADDRESSEERobert J. Brady Co.A Prentice-H<strong>al</strong>l CompanyBowie, Maryland 20715· · · - -· · · · ·oX =USR(C).·- . . .. .. ... "v' uc ,._,, .. ,lcu 11 1111 e 1 011J 1::. cnangea IO reaa lb!J17 VTAB (22) : PRINT "ALL DONE"The VT B has been changed to 22 to <strong>al</strong>low program line 172 to print onscreen line 23, and the GOTO has been removed since the program nolonger ends at this point.172 PRINT 11 ANOTHER CHARACTER? ( Y/N) ": GET R$
CHAPTER 4-APPLESOFT EXTENSIONS 29174 IF R$ = "Y" GOTO 134176 IF R$ = "N" GOTO 25(J178 PRINT CHR$ ( 7) : GOTO 172These lines inquire wh<strong>et</strong>her the user wants to try another character; if yesthen GOTO line 134 to restart, if no then GOTO the END statement, and ifneither then beep the bell and try for another response.2(J5 DATA 32,12,225The three new data v<strong>al</strong>ues discussed with line 7©.24(J DATA 2(J ,3,96The fi rst piece of data i this line is different than in Listing 4-3.The subroutine which prints the characters for Listings 4-3 and 4-4 isonly slightly faster than the BASIC program in Listing 4-1, which <strong>al</strong>so fi llsthe screen with a selected character. However, it is worth noting that themachine level subroutine used has been slowed down by a factor ofapproximately 125 so that the process will take a noticeable amount oftime. To help demonstrate the speed of execution fo r machine level routines,replace each of the fi rst four data v<strong>al</strong>ues in line 23(/J with the v<strong>al</strong>ue234, to disable the delay fu nction, and then run the modified program.VocabularyCALLPEEKPOKEUSRExercises1. Write a BASIC program to d<strong>et</strong>ermine the v<strong>al</strong>ues at memory locations1©2©, 1©21, 1©22, and 1©23.2. Write a BASIC program to poke the following v<strong>al</strong>ues into memorylocations 462(/J through 4677.32, 88, 252, 169, 217, 32, 24(J , 253, 169, 2(J7, 32, 24(J , 253, 169,213, 32, 24(J , 253, 169, 16(J , 32, 24(J , 253, 169, 196, 32, 24(J , 253,169, 2(Jl, 32, 24(J , 253, 169, 196, 32, 24(J , 253 , 169, 16(J , 32, 24(J ,253, 169, 2(Jl, 32, 24(J , 253, 169, 212 , 32, 24(J , 253, 169, 161, 32,24(J , 2533. Alter the program written in Exercise 2 so that it places the machinecode v<strong>al</strong>ues into memory and then executes them as a subroutine.
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