DECLARE SUB SHELLSORT (X%(), N%)
DEFINT A-Z
CLS
DIM A(20)
FOR J = 0 TO 19
  A(J) = INT(20 * RND): PRINT USING "####"; A(J);
NEXT J
PRINT
SHELLSORT A(), 20
FOR J = 0 TO 19: PRINT USING "####"; A(J); : NEXT J
END


SUB SHELLSORT (X%(), N%)
  DIM I, J, GAP, K, XX, A(5)
  A(0) = 9: A(1) = 5: A(2) = 3: A(3) = 2: A(4) = 1
  FOR K = 0 TO 4
    GAP = A(K)
    FOR I = GAP TO N - 1
      XX = X(I)
      FOR J = I - GAP TO 0 STEP -GAP
        IF XX >= X(J) THEN EXIT FOR
        X(J + GAP) = X(J)
      NEXT J
      X(J + GAP) = XX
    NEXT I
  NEXT K
END SUB