Convert date type 7 to a number

A type 7 date is stored as CHR(YY+1) + CHR(MM+1) + CHR(DD+1). This program decodes one into a YYMMDD string, then converts it to a number with DTN and back with NTD.

00005 REM " Change from date type 7 to a number
00010 A$=CHR(97+1)+CHR(11+1)+CHR(1+1)  !let A$ equal a pre-defined type 7 date
                                       !which is stored as...
                                       !CHR(YY+1) + CHR(MM+1) + CHR(DD+1)

00020 B$=STR(ASC(A$(1,1)));            !let B$ equal the string of the year
      C$=STR(ASC(A$(2,1)));            !let C$ equal the string of the month
      D$=STR(ASC(A$(3,1)))             !let D$ equal the string of the day

00030 BB$=STR(NUM(B$)-1);              !subtract 1 from the string of BB$
      CC$=STR(NUM(C$)-1);              !subtract 1 from the string of CC$
      DD$=STR(NUM(D$)-1)               !subtract 1 from the string of DD$

00035 IF LEN(BB$)=1                    !test to see if the year is one digit
         BBB$="0"                      !if it is, place a zero before it
      ELSE
         BBB$=""
00040 IF LEN(CC$)=1                    !test to see if the month is one digit
         CCC$="0"                      !if it is, place a zero before it
      ELSE
         CCC$=""
00045 IF LEN(DD$)=1                    !test to see if the day is one digit
         DDD$="0"                      !if it is, place a zero before it
      ELSE
         DDD$=""
00050 E$=BBB$+BB$+CCC$+CC$+DDD$+DD$    !let E$ equal the sum of the strings
00055 N=DTN(E$,"YYMMDD");              !let N equal the number from the string
      N$=NTD(N,"YYMMDD")               !let N$ equal the date from the number
00060 PRINT N,N$
00070 INPUT *

Notes

Line 00010 builds a sample type 7 date (November 1, 1997). In your own program, take the three bytes from your data instead.