10 REM Binary search
20 DIM A(10)
30 N% = 10
40 FOR I% = 0 TO 9: READ A(I%): NEXT I%
50 REM Sorted data
60 DATA -31, 0, 1, 2, 2, 4, 65, 83, 99, 782
70 X = 2: GOSUB 500
80 GOSUB 200
90 X = 5: GOSUB 500
100 GOSUB 200
110 END
190 REM Print result
200 PRINT X;
210 IF INDX% >= 0 THEN PRINT "is at index"; STR$(INDX%);"." ELSE PRINT "is not found."
220 RETURN
480 REM Binary search algorithm
490 REM N% - number of elements; X - searched element; Result: INDX% - index of X
500 L% = 0: H% = N% - 1: FOUND% = 0
510 WHILE (L% <= H%) AND NOT FOUND%
520  M% = L% + (H% - L%) \ 2
530  IF A(M%) < X THEN L% = M% + 1 ELSE IF A(M%) > X THEN H% = M% - 1 ELSE FOUND% = -1
540 WEND
550 IF FOUND% = 0 THEN INDX% = -1 ELSE INDX% = M%
560 RETURN