Commodore VIC-20 User Manual page 155

Chapter 4 Advanced BASIC Programming
141
Lines 200 through 230 have the same structure as any of the other five
statement groups.
200 REM GET 12 CHARACTER NAME
210
R~=3:
C?=9:
L~I?=12:
GOSUB 8000
220
~IAS"'CC$
230 IF
EDITING~
THEN 500
Line 210 assigns values to variables and peforms a GOSUB to line 8000.
Line 8000 is a data entry subroutine; it uses variables R % and C% to specify
where on the screen the data entry will occur. LN% contains the maximum
length of the entry. Line 220 assigns the entered data to NA$, the string
variable to hold the name.
Line 230 is a logical test which you can ignore for now; it will be
explained shortly.
Now check the group starting at line 250. Although the values assigned to
R%, C%, and LN% may differ and line 270 is not exactly the same, the
structure oflines 250-280 is identical to that oflines 200-270. This is the case
for all of the other statement groups.
EDITING DATA ENTRY UNES
Once all six lines are entered, the program displays ANY CHANGES?
and waits for a response of Y or N. If the response is N, the program will
clear the screen and end. If the response is Y, the program will ask which
entry line needs to be changed. At this point, the operator can change any
entry lines at random until all lines are correct.
The following lines of the data entry program in Figure 4-2 perform
these steps:
500 REM ASK IF ANY CHANGES ARE TO
BE
MADE
510 EDITlNO:'::=-l
520
R~=10:C~=0:00SUB ~000
530
QU$="
ANY CHANGES?
II"
540 OOSUB 3000:REM GET "Y" OR "N"
550
IF
C$="N" THEN PRINT
":'l"; :
END
560 REM ASK WHICH LINES NEED CHANGING
570
QUS="WHICH LINE
(1-6)7: II"
580
R~=12:LO~=1:HI~=6
390 OOSIJB 3500
600 ON NM? GOTO 200,250,300,350,400,450
610 OOTO 520
Line 510 is of special interest because it "switches on" the editing