ShellSort.bas

REM
REM shellsort.bas
REM
REM illustrate the usage of arrays
REM in HiSOFT/MaxonBASIC OR QBasic/QB64
REM

DEFINT A-Z

REM define arrays
DIM UnsortedList$(10) ' holds unsorted characters
DIM SortedList$(10)

REM DECLARE functions AND sub-programs
DECLARE SUB Shell_Sort(Words$(1))

REM -- Program work starts here --
MainProgram:
CLS
PRINT "ShellSort in Basic"
PRINT "==================": PRINT

REM -- Fill array --
UnsortedList$(0) = "9"
UnsortedList$(1) = "3"
UnsortedList$(2) = "5"
UnsortedList$(3) = "4"
UnsortedList$(4) = "7"
UnsortedList$(5) = "1"
UnsortedList$(6) = "8"
UnsortedList$(7) = "2"
UnsortedList$(8) = "6"
UnsortedList$(9) = "0"

REM -- PRINT unsorted array --
PRINT "Unsorted List: ";
FOR i = 0 TO (UBOUND(UnsortedList$, 1))
    PRINT UnsortedList$(i);
    NEXT i
    PRINT

REM -- Shell-sort the LIST AND copy it into a new array --
FOR i = 0 TO (UBOUND(UnsortedList$, 1))
    CALL Shell_Sort(UnsortedList$())
    SortedList$(i) = UnsortedList$(i) ' also copy content to 2nd array!
    PRINT UnsortedList$(i)
NEXT i

REM -- PRINT sorted array --
PRINT "Sorted List: ";
FOR i = 0 TO (UBOUND(UnsortedList$, 1))
    PRINT UnsortedList$(i);
NEXT i
PRINT

REM -- PRINT sorted array --
PRINT "New Sorted List: ";
FOR i = 0 TO (UBOUND(SortedList$, 1))
    PRINT SortedList$(i);
NEXT i
PRINT

Rem -- ShellSort --
SUB Shell_Sort (Words$( 1))
    STATIC HowFAR, Top, i, j
    Top = UBOUND(Words$)
    HowFAR = Top \ 2

    DO WHILE HowFAR > 0
        FOR i = HowFAR TO Top - 1
            j = i - HowFAR + 1
            FOR j = (i - HowFAR + 1) TO 1 STEP - HowFAR
                IF Words$(j) <= Words$(j + HowFAR) THEN
                    EXIT FOR
                END IF
            SWAP Words$(j), Words$(j + HowFAR)
            NEXT j
        NEXT i

        HowFAR = HowFAR \ 2
    LOOP
END SUB