REM Binary search
DIM A(10)
REM Sorted data
DATA -31, 0, 1, 2, 2, 4, 65, 83, 99, 782
FOR I = 0 TO 9
  READ A(I)
NEXT I
N = 10
X = 2
GOSUB DoBinarySearch:
GOSUB PrintResult:
X = 5
GOSUB DoBinarySearch:
GOSUB PrintResult:
END

PrintResult:
PRINT X;
IF IndX >= 0 THEN
  PRINT " is at index ";
  PRINT IndX;
  PRINT "."
ELSE
  PRINT " is not found."
ENDIF
RETURN

DoBinarySearch:
REM Binary search algorithm
REM N - number of elements
REM X - searched element
REM Result: IndX - index of X
L = 0
H = N - 1
Found = 0
Loop:
  IF L > H THEN AfterLoop:
  IF Found <> 0 THEN AfterLoop:
  REM (L <= H) and (Found = 0)
  M = H - L
  M = M / 2
  M = L + M
  REM So, M = L + (H - L) / 2
  IF A(M) < X THEN
    L = M + 1
  ELSE
    IF A(M) > X THEN
      H = M - 1
    ELSE
      Found = 1
    ENDIF
  ENDIF
  GOTO Loop:
AfterLoop:
IF Found = 0 THEN
  IndX = -1
ELSE
  IndX = M
ENDIF
RETURN