DECLARE SUB sethash (tag$, value$)
DECLARE FUNCTION hash$ (s$)
DECLARE FUNCTION mkhash! (s$)
' Created:06-24-00
' By Jeff Connelly

' Associative arrays (sometimes known as hashes) used in QBasic

' This is called associative arrays, and was inspired by GTSC4's question
'
' To retreive a value, use hash$("key")
' To set a value, use sethash("key", "value")
' [QBasic is not extendable enough to allow hash$("key") = "value"]

' This does not need to be accessed directly
DIM SHARED hasharray$(60)

' Example program
CLS
PRINT "Associative Array Example"
PRINT
DO
    PRINT
    DO
        INPUT "Key to set: ", key$
    LOOP WHILE mkhash(key$) > 60
    INPUT "Value to set key to: ", value$
    sethash key$, value$
    PRINT
    PRINT "Hash values: "
    FOR i = 1 TO UBOUND(hasharray$)
        IF (LEN(hasharray$(i)) > 0) THEN PRINT , i, hasharray$(i)
    NEXT
    PRINT
    INPUT "Key to retreive: ", key$
    PRINT , key$ + " is " + hash$(key$)
LOOP


FOR i = 1 TO 14
    key$ = STRING$(i, 255)
    ' Key must be around less than 15 characters at most
    sethash key$, "bar"
    PRINT hash$(key$)
NEXT

FUNCTION hash$ (s$)
hash$ = hasharray$(mkhash(s$))
END FUNCTION

FUNCTION mkhash (s$)
' Return the checksum of the data in S$.  Could use work.  Needs to change
' as much as possible even with one bit of change in the data.  CRC32 has
' a good polynomial, and CRC16 too, but they are too large for this purpose.
DIM ret AS INTEGER
FOR i = 1 TO LEN(s$)
    c$ = MID$(s$, i, 1)
    c = ASC(c$)
    IF (i MOD 1) THEN rr = ret ELSE rr = -ret
    ret = rr + (c * (i / 2)) + i
NEXT
' Make the hash within 0..60 for the array
ret = INT(ret / 16)
IF (ret > 60 OR ret < 0) THEN
    PRINT "mkhash: error: key too large: " + s$
    ret = 0
END IF
mkhash = ret
END FUNCTION

SUB sethash (key$, value$)
' The longest key can be is 14 characters at minimum, depends on bytes
hasharray$(mkhash(key$)) = value$
END SUB