10 REM Binary search
20 LET N = 10
30 FOR I = 1 TO N
40 READ A(I)
50 NEXT I
60 REM Sorted data
70 DATA -31, 0, 1, 2, 2, 4, 65, 83, 99, 782
80 LET X = 2
90 GOSUB 500
100 GOSUB 200
110 LET X = 5
120 GOSUB 500
130 GOSUB 200
140 END

190 REM Print result
200 PRINT X;
210 IF I1 < 0 THEN 240
220 PRINT "is at index"; I1; "."
230 RETURN
240 PRINT "is not found."
250 RETURN

460 REM Binary search algorithm
470 REM N - number of elements
480 REM X - searched element
490 REM Result: I1 - index of X
500 LET L = 0
510 LET H = N-1
520 LET F = 0
530 LET M = L
540 IF L > H THEN 650
550 IF F <> 0 THEN 650
560 LET M = L+INT((H-L)/2)
570 IF A(M) >= X THEN 600
580 LET L = M+1
590 GOTO 540
600 IF A(M) <= X THEN 630
610 LET H = M-1
620 GOTO 540
630 LET F = 1
640 GOTO 540
650 IF F = 0 THEN 680
660 LET I1 = M
670 RETURN
680 LET I1 = -1
690 RETURN