10 DATA 2,3,5,6,8,10,11,15,19,20
20 DIM t(10)
30 FOR i=1 TO 10
40 READ t(i)
50 NEXT i
60 LET value=4: GO SUB 100
70 LET value=8: GO SUB 100
80 LET value=20: GO SUB 100
90 STOP
100 REM Binary search
110 LET lo=1: LET hi=10
120 IF lo>hi THEN LET idx=0: GO TO 170
130 LET middle=INT ((hi+lo)/2)
140 IF value<t(middle) THEN LET hi=middle-1: GO TO 120
150 IF value>t(middle) THEN LET lo=middle+1: GO TO 120
160 LET idx=middle
170 PRINT "Value ";value;
180 IF idx=0 THEN PRINT " not found": RETURN
190 PRINT " found at index ";idx: RETURN