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'These three examples use DO...LOOP to show how the placement of the
'condition affects the number of times the block of statements is executed,
'to illustrate testing at the end of a loop, and to present a SUB procedure
'where an ending test is appropriate.
 
DIM I AS INTEGER
CLS
'In this example, the test is done at the beginning of the loop.
'Because I is not less than 10, the body of the loop (the
'statement block) is never executed.
 
'DO...LOOP with test at the top of the loop.
'Output shows that loop was not executed.
I = 10
PRINT "Example 1:": PRINT
PRINT "Value of I at beginning of loop is  "; I
DO WHILE I < 10
   I = I + 1
LOOP
PRINT "Value of I at end of loop is  "; I
 
'The following example tests I at the end of the loop, so the
'statement block executes at least once.
 
'DO...LOOP with test at the bottom of the loop.
'Output shows loop was executed once.
I = 10
PRINT : PRINT : PRINT "Example 2:": PRINT
DO
   PRINT "Value of I at beginning of loop is  "; I
   I = I + 1
LOOP WHILE I < 10
PRINT "Value of I at end of loop is  "; I
 
'The following sort program tests at the end of the loop because
'the entire array must be examined at least once to see if it is in
'order. In general, test at the end of a loop only if you know that
'you always want the statement block executed at least once.
 
'Set up a special value to indicate no exchanges.
CONST NOEXCH = -1
DIM Exes(12)
'Load the array and mix it up.
FOR I = 1 TO 12 STEP 2
   Exes(I) = 13 - I
   Exes(I + 1) = 0 + I
NEXT I
Limit = 12
PRINT : PRINT : PRINT "Example 3:": PRINT
PRINT "This is the list of numbers to sort in ascending order:"
PRINT
FOR I = 1 TO 12
   PRINT USING " ### "; Exes(I);
NEXT I
PRINT
'In the following DO...LOOP, INKEY$ is tested at the bottom of the loop.
'When the user presses a key, INKEY$ is no longer a null string and the
'loop terminates, continuing program execution.
 
'DO...LOOP with test at the bottom of the loop.
PRINT : PRINT "Press any key to continue."
DO
LOOP WHILE INKEY$ = ""
 
DO
   Exchange = NOEXCH
   FOR I = 1 TO Limit - 1            'Make one pass over the array.
      IF Exes(I) > Exes(I + 1) THEN
         SWAP Exes(I), Exes(I + 1)   'Exchange array elements.
         Exchange = I                'Record location of most
      END IF                         'recent exchange.
   NEXT I
   Limit = Exchange                  'Sort on next pass only to where
                                     'last exchange was done.
LOOP UNTIL Exchange = NOEXCH         'Sort until no elements are exchanged.
 
PRINT : PRINT "Sorting is completed. This is the sorted list:": PRINT
FOR I = 1 TO 12
   PRINT USING " ### "; Exes(I);
NEXT I
END