SWAP Statement Programming Example
 
The following program sorts the elements of a string array in descending
order using a Shell sort. It uses SWAP to exchange array elements that are
out of order.
 
' Sort the word list using a Shell sort.
Num% = 4
Array$(1) = "New York"
Array$(2) = "Boston"
Array$(3) = "Chicago"
Array$(4) = "Seattle"
Span% = Num% \ 2
DO WHILE Span% > 0
    FOR I% = Span% TO Num% - 1
    J% = I% - Span% + 1
        FOR J% = (I% - Span% + 1) TO 1 STEP -Span%
            IF Array$(J%) <= Array$(J% + Span%) THEN EXIT FOR
            '
            ' Swap array elements that are out of order.
            '
            SWAP Array$(J%), Array$(J% + Span%)
         NEXT J%
    NEXT I%
    Span% = Span% \ 2
LOOP
CLS
FOR I% = 1 TO Num%
    PRINT Array$(I%)
NEXT I%
END
 
This program could be converted into a useful SUB, which would sort a
string array of any size, by using the SUB...END SUB statements as shown
below:
 
' Sort the word list using a Shell sort.
SUB ShellSort (Array$(), Num%) STATIC
   Span% = Num% \ 2
   DO WHILE Span% > 0
      FOR I% = Span% TO Num% - 1
         J% = I% - Span% + 1
         FOR J% = (I% - Span% + 1) TO 1 STEP -Span%
            IF Array$(J%) <= Array$(J% + Span%) THEN EXIT FOR
            ' Swap array elements that are out of order.
            SWAP Array$(J%), Array$(J% + Span%)
         NEXT J%
      NEXT I%
      Span% = Span% \ 2
   LOOP
END SUB