10 DIM n(10): LET c$=""
20 FOR i=1 TO 4
30 LET d=INT (RND*9+1)
40 IF n(d)=1 THEN GO TO 30
50 LET n(d)=1
60 LET c$=c$+STR$ d
70 NEXT i
80 LET guesses=0
90 INPUT "Guess a 4-digit number (1 to 9) with no duplicate digits: ";guess
100 IF guess=0 THEN STOP
110 IF guess>9999 OR guess<1000 THEN PRINT "Only 4 numeric digits, please": GO TO 90
120 LET bulls=0: LET cows=0: LET guesses=guesses+1: LET g$=STR$ guess
130 FOR i=1 TO 4
140 IF g$(i)=c$(i) THEN LET bulls=bulls+1: GO TO 160
150 IF n(VAL g$(i))=1 THEN LET cows=cows+1
160 NEXT i
170 PRINT bulls;" bulls, ";cows;" cows"
180 IF c$=g$ THEN PRINT "You won after ";guesses;" guesses!": GO TO 10
190 GO TO 90