Commodore VIC-20 - Page 148

134 The VIC 20 User Guide
of the date. The two-digit input needs no RETURN or other terminating
character. The program automatically terminates the
data entry after two
characters are entered.
Two-digit entries are needed for the month, the day, and the year.
Rather than repeating statements in lines
20 through 50, you could put these
statements into a subroutine and branch to it three times, as follows:
10 PRINT ":'111 !!-III !!-III !!"; CHR$(13); "1";
20 GOSUB 1000:MM$=TC$:PRINTTAB(3)
30 GOSUB 1000:DD$=TC$:PRINTTAB(6)
40 GOSUB1000:YY$=TC$
50 STOP
1000 REM TWO CHARACTER INPUT SUBROUTINE
1010 GET C$: IF C$="" THEN 10113
1020 PRINT C$;
1030 GET CC$:IF CC$"''''' THEN 1030
1040 PRINT CC$;
1050 TC$==C$+CC$
1060 RETURN
The variables MM$, DD$, and YY$ hold the month, day, an~ year entries,
respectively. Each entry
is held as a two-character string. You should empty
the input buffer before accepting the first input; otherwise, any prior charac-
ters in the input buffer will be read by the first GET statement in the
two-character input subroutine. You need
to empty the buffer only once
before the first GET statement. .
There are two ways to help the operator recover from errors while
entering a date .
• The program can automatically test for valid month, day, and year
entries.
. The operator can restart the data entry by pressing a specific key.
The program can check that the month lies between
01 and 12. The
program will not bother with leap years, but will check for the maximum
number of days in the specified month. Any year from
00 through 99 is
allowed. Any invalid entry restarts the entire date entry sequence. Also, if
the operator presses the RETURN key, the entire date entry sequence restarts.
The final date entry program now appears in Figure 4-1.
Notice that the date
is built up in the 8-character string DT$ as month,
day, and year are entered.