PLAYER = 1
COMP   = 0
RANDOMIZE TIMER

sum = 0
total = 0
turn = INT(RND + 0.5)
DIM precomp(0 TO 3)
precomp(0) = 1 : precomp(1) = 1
precomp(2) = 3 : precomp(3) = 2

WHILE sum < 21
    turn = 1 - turn
    PRINT "The sum is "; sum
    IF turn = PLAYER THEN
        PRINT "It is your turn."
        WHILE total < 1 OR total > 3 OR total + sum > 21
            INPUT "How many would you like to total? ", total
        WEND
    ELSE
        PRINT "It is the computer's turn."
        total = precomp(sum MOD 4)
        PRINT "The computer totals"; total; "."
    END IF
    PRINT
    sum = sum + total
    total = 0
WEND

IF turn = PLAYER THEN
    PRINT "Congratulations. You win."
ELSE
    PRINT "Bad luck. The computer wins."
END IF